The Synthesis and Characterization of a Novel Single Source Beta-Barium Borate Precursor Barium (18-Crown-6) Dimesitylborinate Travis M
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2007 The synthesis and characterization of a novel single source beta-barium borate precursor barium (18-crown-6) dimesitylborinate Travis M. Scott
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This Thesis is brought to you for free and open access by the Thesis/Dissertation Collections at RIT Scholar Works. It has been accepted for inclusion in Theses by an authorized administrator of RIT Scholar Works. For more information, please contact [email protected]. The Synthesis and Characterization of a Novel Single Source
Beta-Barium Borate Precursor Barium (l8-crown-6) Dimesitylborinate
Travis M. Scott
Thesis
Submitted for Partial Fulfillment of the Requirements for the Degree in Master of
Science
Approved:
M. L. IIlingsworth
Thesis Advisor T. C. Morrill
Department Head
Department of Chemistry
Rochester Institute of Technology
Rochester, New York
February 13 , 2007 Thesis/Dissertation Author Permission Statement
Title of thesis or dissertation: ike s'jl)tkes I ~ (tAd C~cJe f' r2(A hOI\ 4- C\. N()ve-l&tGt- B ">I'-I \...lJV\ J3(;1."G1.k- ~ C'e..0- v,.I'5<:"":';----- 1)o.!'I v-MC t~ -tNk".J) .... tD) D 1 Me-s, I-~I bc?('-.I t\o.te
.-;. .... <./ . Name of author: 11\\ VI ~ 1'1 . _J( crit Degree: ·scMI McI5/-es'C) eIw'.'16tt\j I §5 H/c)Clv:"-'11lst (\~ Program: LhQ/b Istt-u College: _s_""' -"'c_,e..='1-'-'cc,"-"-_J______
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Signature of Author: ______Travis M. Scott Date: vr? I'")..::J I /07 Table of Contents
Page
? Introduction 1
? Experimental
Materials: 14 _ _
Reaction Scheme: 16
Synthesis of Barium ( 1 8-Crown-6) Dimesitylborinate: 1 6
Testing the Reaction by TLC: 19
Isolation of Barium (18-Crown-6) Dimesitylborinate via
Recrystalization: 20
Isolation of Barium ( 1 8-crown-6) Dimesitylborate via Column
Chromatography: 20
Characterization of Barium ( 1 8-crown-6) Dimesitylborinate: 21
Crystal Growth of Barium (18-crown-6) Dimesitylborainte:
Converting Barium (18-crown-6) Dimesitylborinate to
Beta-Barium Borate:. 23
Preparation of Thin Films of BBO: 24
? Results and Discussion
o Confirmation of Isolation: 24
Confirmation for Barium and Boron in
Barium (18-crown-6) Dimesitylborinate: 24
o Identification of coloration: 25 Single Crystal Structure of Hydrolyzed
o Barium (18-crown-6) Dimesitylborinate:
Characterization of Barium ( 1 8-crown-6) Dimesitylborinate via
Infrared Spectroscopy: 28
Characterization of Barium (18-crown-6) Dimesitylborinate via
Nuclear Magnetic Resonance: 34
Characterization of Barium (18-crown-6) Dimesitylborinate via
Thermogravimetric Analysis (TGA): 42
Characterization of Barium (18-crown-6) Dimesitylborinate via
Characterization of Barium ( 1 8-crown-6) Dimesitylborinate by
Elemental Analysis: 44
Characterization of Barium ( 1 8-crown-6) Dimesitylborinate via
Mass Spec: 46
X-ray Diffraction of Heated Powders: 49
X-ray Diffraction of Thin Films: 49
? Conclusions 57
? Future Work __ 58
? References 59 List of Figures
Figure # Page
4 Figure 1 . (3-BBO Structure
Figure 2. Crystal Structure of (enH2)i.5[Ba(hfa)5]C2H5OH 1
Figure 3. Crystal Structure of
Bis(hexafluoroacetylacetonate)(crown 12 Barium ether) _
Figure 4. Proposed Single Source Precursor,
Barium (18-crown-6) Dimesitylborinate. 14
Figure 5. Design of Reaction Apparatus
Figure 6. Crystal Structure of Hydrolysis Product.. 28
of Crystal Structure 28 Figure 7. Molecular View Hydrolyzed Products ._
of Dimesitylborinic Acid Figure 8. IR Spectrum _ _
Figure 9. IR Spectrum of 18-crown-6 32
Figure 10. IR Spectrum of Barium (18-crown-6) Dimesitylborinate.. 33
. of D-chloroform 36 Figure 1 1 NMR Spectrum __ _
of Dimesitylborinic Acid 37 Figure 12. NMR Spectrum _
Figure 13. NMR Spectrum of 18-crown-6 38
Figure 14. NMR Spectrum of Barium (18-crown-6) Dimesitylborinate
obtained from Column Chromatography 39
Figure 15. NMR Spectrum of Barium (18-crown-6) Dimesitylborinate
obtained from Hexanes 40
Figure 16. TGA Scan of Barium (18-crown-6) Dimesitylborinate 43
m Figure 17. Mass Spectrum of Barium (18-crown-6) Dimesitylborinate
Figure 18. Product Crystals Heated to 550C 50
Figure 19. Initial Product Crystals Heated to 800C 51
Figure 20. Second Product Crystals Heated to 800C 52
Figure 21. Second Product Crystals Heated to 800C
Figure 22. Product Residue Heated to 550C 54
Figure 23. Washed Product Residue Heated to 800C.___. 55
Figure 24. XRD Thin Films on Sapphire Substrate .... 56
IV List of Tables
Table # Page
Table I. Physical and chemical properties
of NLO crystals 3
Table II. Thin films compared to bulk crystals 5
Table III. Comparison between different
thin film techniques 7
Table IV. Notable Research towards the development
of BBO Thin Films 9
Table V. Heating cycle for converting precursor to BBO 23
Table VI. X-ray crystallography data for
hydrolyzed product C30O8H55B 27
Table VII. NMR data comparing starting materials to product 41
Table VIII. Elemental Analysis of Barium (18-crown-6)
Dimesitylborinate 44 List of Abbreviations
BBO Barium Borate (BaB208)
CE 18-crown-6
DMBA Dimesitylborinic acid
DSC Differential Scanning Calorimetry
IR Infrared
MOCVD Metal Organic Chemical Vapor Dc
MOD Metallorganic decomposition
MSP Multi-source Precursor
NLO Non-linear Optical
NMR Nuclear Magnetic Resonance
SSP Single Source Precursor
SHG Second Harmonic Generation
TGA Thermal Gravimetric Analysis
THG Third Harmonic Generation
TLC Thin Layer Chromatography
UV Ultra Violet
XRD X-ray Diffraction
VI Acknowledgements
I would first like to thank Dr. Illingsworth, my research advisor. He was an invaluable help at interpreting and understanding the results of the research. I would like to thank Dr. Gysling for his support and help throughout the research. I would like to thank Dr. Langner for his advice and lessons throughout my education. I would like to thank Dr. Smith for all he has done to help me through the Masters degree program.
I would like to thank Krista Fridman for all her advice and ideas while working
on this thesis.
I would like to thank Tom Blanton from Eastman Kodak Research Laboratories for recording thin film XRD.
I would like to thank Thomas lackson and Robert Saccente from Eastman Kodak
Research Laboratories for their help obtaining and interpreting mass spectroscopy.
I would like to thank Dr. Morrill and Brenda K. Mastrangelo for their help and assistance throughout my education here.
I would like to thank all the professors and faculty members who I have met, learned from, and worked with.
I would like to thank my family and friends for their support and help.
vn Abstract
Nonlinear optical materials are a rapidly growing market and are expected to exceed $1.6 billion by 2009. Significant time, energy, and investment have been applied to increasing the efficiency of producing NLO materials. Of these materials beta-barium borate has stood out as an important NLO product.
The goal of this research was the development of a novel beta-barium precursor
suitable for applications in thin film technology. Special attention was paid towards
development of a precursor suitable for metal organic chemical vapor deposition. To that
end special attention was paid towards the synthesis of a mononuclear barium compound.
The novel BBO precursor obtained was a barium dimesityl borate compound
coordinated with 18-crown-6, barium (18-crown-6) dimesitylborinate (BaB2C4g08H68).
The apparently water-sensitive precursor has shown conversion to BBO comparable to
current industrial processes.
vui Introduction
The development and application of non-linear optical (NLO) materials is responsible for a rapidly growing market in the chemical and material industries. The current estimated global market value in NLO materials is estimated to be $856 million and is projected to exceed $1.6 billion by 2009. The cause for the rapid increase in the
NLO materials global market is related to the utilization of NLO in the fields of
electro-optics.1 telecommunications and
NLO materials have unique properties which produce a shift in incident laser light frequency. Special attention has been shown to second harmonic generation (SHG) and higher harmonic generation (HHG) materials. SHG and HHG materials have been shown
to allow for the conversion of incident visible region laser frequencies to ultraviolet (UV)
frequencies. Laser frequencies in the UV region are desirable due to their application as
' in communications and high density data storage.
A harmonic generation material interacts with a fundamental frequency in such a
way as to cause the doubling (SHG), tripling (THG), or higher order (HHG) increase of
the frequency due to nonlinear optical properties of the material. Equation 1, relates the
induced dielectric polarization to an applied field.
%(2)E2 P(E) = Ep(X(1)E + + X(3)E3+ ) (1) xU) where P represents the induced dielectric polarization, E is the applied field, is the
%(2) linear dielectric susceptibility, is the nonlinear dielectric susceptibility of the second
x<3) etc.4 order, and is the nonlinear dielectric susceptibility of the third order,
The NLO response arises from the interaction of a NLO material with an oscillating electric field. Provided that the incoming oscillating electric field has a large enough amplitude and intensity, the resulting radiation emitted from the NLO material is
a combination of the incoming oscillating electric field and the harmonic generation
produced by the NLO material. This resulting interaction causes NLO materials to emit
4 different wavelengths of light than the incident light.
There are several NLO materials commercially available. A list of 5 important NLO
materials available from Fujian Castech Crystals, Inc. is shown in Table I. Fujian
Castech Crystals, Inc. is the largest supplier of lithium borate (LiB305, LBO), barium
borate Potassium Titanyl and (BaB206, BBO), Phosphate (KTiOP04, KTP) , Neodymium
worldwide.3-4 Doped Yttrium Orthovanadate (Nd:YV04) crystals 3,4 Table I. Physical and Chemical Properties of NLO crystals
NLO crystal Crystal Transparency Damage SHG
Structure Range Threshold coefficient
GW/cra2 BaB204 R3c 189-3500 nm 5 d22 = 2.3
d3i = 0.16
KTiOP04 Pna2 350-4500 nm 0.9-1.0
GW/cm2
GW/cm2 LiB305 Pna2 155-3200 nm >0.9 d31 = 0.67
d32 = 0.85
d33 = 0.04
GW/cm2 KH2P04 174-1570 nm 0.25
GW/cm2 LiNb03 R3c 400-5500 nm 0.3
GW/cm2 BiB306 Point group 2 286-2500 nm >0.3
BBO compares favorably to other commercially available NLO materials by
having a large transparency range, coupled with a large SHG coefficient (Table I). In
addition, BBO's damage threshold is significantly larger than other NLO materials, especially at UV wavelengths.
BBO exists primarily in two crystalline forms; a-BBO and P-BBO. a-BBO forms
at temperatures above 925C and has a centrosymmetric structure. Because this structure has a center of symmetry it does not exhibit any NLO properties. A third from, y-BBO, has been reported to exist below temperatures of 500 C as a chain anion structure; however no detailed structured has been reported. y-BBO also does not exhibit any NLO
properties.5
P-BBO has acentric symmetry and belongs to the space group R3c. p-BBO forms
between temperatures of 500 and 925 C. P-BBO has a structure consisting of alternating
" Ba and (B306) rings forming a layer step crystal lattice. The key distinction between
a-BBO and P-BBO is the coordination of barium to oxygen, the a form having barium
form.5 coordination numbers of 9 and 6 versus 8, for the P A structure of P-BBO can be
seen in Figure 1 .
Figure 1. p-BBO Structure6 BBO has been used in both single crystal and thin film forms for SHG frequency conversion. Table II compares the advantages and disadvantages of thin films vs.
crystals.
Table II. Thin films compared to crystals
Thin Films Crystals
Advantages -Conversion to beta for -Grown in industrialized
9 reported at 500-550C scale
-Applications include -Useful for laser frequency
frequency converters, conversion
waveguides, and storage -can be prepared with high
devices purity
-High purity products
-Precise composition
control
Disadvantages -Precursor for BBO must -Defects in crystals result in
have applicable properties poor NLO material
to development of thin -Visibly flawless crystals
films can result in light
scattering
-Sometimes difficult to
grow crystals in a
predetermined
configuration The fabrication of high quality thin films of BBO is desirable for their application
waveguides.7 involving integrated optical devices. These films could possible act as UV
There are currently several methods used to prepare thin films of p-BBO. The four main methods used for developing thin films are chemical vapor deposition (CVD), metal organic decomposition (MOD), spray CVD, and sol-gel processing. Table III
method.7"10 illustrates the advantages and disadvantages of each
An important goal in the development of a suitable precursor for a nonlinear optical material is that is be derived from a single source; i.e. a single source precursor
(SSP). A single source precursor is a compound that contains the correct stoichiometric
amount of each element needed for the final product in a single molecular compound.
The alternative to using a SSP is using a multi-source precursor (MSP).
There are certain advantages and disadvantages when comparing a SSP to a MSP.
By using a SSP the stoichiometric amount of each element is accounted for and will be present when converting to the desired NLO material. This is essential due to the nature of processes for development of NLO materials. By using MSPs there is no guarantee of delivering the required stoichiometric amount of each element to the NLO reaction site, and thereby resulting in an incomplete conversion to the desired NLO material. MSPs will have different properties for each of the compounds involved. This is both a postive and negative, as it allows for a greater selection of source precursors, but because the different sources have different physical and chemical properties it makes the timely delivery of the appropriate amounts to the reaction site difficult. Table III. Comparison between different thin film techniques
Technique Advantage Disadvantage
CVD -Produces high quality thin -Requires volatility of
films precursors
-Allows for in situ doping -Precise process control
of product during crystal required to control molar
growth and accurate amounts at reaction site
control over defect content when using more than one
source precursor
Spray CVD -Reaction is uniform over -Removal of solvents and
substrate organic byproducts
-Applicable to several
industrial applications
MOD -Similar to CVD but does -Requires precursor solution
not require volatility of to have a low viscosity
precursors -Requires removal of a
-Allows for control of solvent from reaction site
volume injected therefore -Generally gives low
controlling stoiciometry at quality films
the reaction site
Sol-gel processing -High purity of product -Crystals formed can be
-Low processing distorted, strained, or
temperature polycrystalline which can
-Precise composition affect optical applications
control -Precursors must have
polymeric characteristics The main requirement for a SSP is developing a compound that contains the correct stoichiometric amount of elements, while containing the desired physical and chemical properties, e.g. volatility and decomposition temperature, suitable for deposition of the target film phase. A MSP would allow for some more choice in selection of precursor reagents than SSPs do. However, this still does not account for the difficulty in
amounts.2 delivering different compounds of the MSP in the correct stoichiometric
For the design and synthesis of suitable BBO precursors, there are several
requirements. The design of the precursor should be subject to the required properties of a specific thin film technique as outlined in Table III. Of special interest among those
SSP.5 techniques are the designs favoring a volatile novel There have been several
attempts to design and synthesize competitive BBO precursors applicable to different thin
film techniques. A list of different research topics and distinct approaches to the
IV.2 9' 10' ' ' development of BBO thin films is presented in Table Table IV. Notable research towards the development of BBO thin films
Research Group Thin Film Conversion Unique features
Technique Temperature
y- Toshinobu Yogo, et Sol-gel method -600 C for ethoxide Conversion from al. using metal system powders BBO to p-BBO at
organic compounds -500 C for ethoxide 500 C
system on Pt
substrate
P- D. B. Studebaker. et MOCVD -720 C for First successful
al. development on BBO thin films
fused silica developed by
MOCVD using
MSP
Takeshi Kobayashi, Chemical solution -650ConSi(100) Identification of
etal. deposition substrates substrate effects on
crystal orientation
P- Person. P. Neves, et Polymeric -650 C on sapphire Only obtained al. precursor substrates BBO in preferred
orientation on
sapphire substrate The first preparation of thin films of P-BBO via MOCVD was reported by
Studebaker, et al. Studebaker developed a precursor solution composed of two reagents,
* triisopropyl borate (B(0'Pr)3) and Ba(thd)2 tetraglyme. The precursor solution was
"flash" delivered via a liquid delivery system to a reactor and vaporized under a nitrogen carrier system to the target substrate. The substrates used were fused silica, platinum,
sapphire, and silicon substrates.
Studebaker determined that the optimal stoichiometry of Ba:B in the precursor
was 1:2.5. The need for excess B was believed to be due to the difference in thermal
stabilities of the different precursors or the volatization of B203 from the developing film.
Studebaker also determined that 95% of the thin films grown were oriented in
[006] direction, which exhibited the largest SHG response. The largest SHG
measurements were on fused silica and sapphire, which showed values of 0.78 and 1 .6
pm/V. These values showed a lower efficiency when compared to bulk BBO, with the
thin films on fused silica and sapphire having relative signals of 17% and 35%,
respectively.
Studebaker made use of a volatile barium compound suitable for MOCVD. There
have been several reports of additional barium compounds suitable for MOCVD
development of thin films. The most volatile barium compounds reported have been P-
diketonate complexes. The complexes share a key property; the majority of barium's
coordination sites were occupied using bulky, chelating ligands to promote a
mononuclear compound.
10 The most volatile barium compound reported was (enH2)i.5[Ba(hfa)5]C2H5OH which vaporized at 280 C with an efficiency of 96-99%. The crystal structure of this
2.13 compound is shown in Figure
CSo
C2S
Figure 2. Crystal structure of (enH2)i.5[Ba(hfa)5]C2H5OH
The crystal structure reveals a barium complex which is mononuclear and is coordinated to 9 oxygen atoms. Four of the coordinated hfa ligands are bidentate ligands accounting
for eight of coordination sites around barium. The ninth is occupied by a fifth hfa ligand
where only one oxygen atom is coordinated to barium. The coordinated ligands are able to prevent any bridging between adjacent barium atoms via steric hindrance while
state.13 fulfilling bariums high coordination
11 A similar compound to (enH2)i.5[Ba(hfa)5]C2H5OH has been made that only has two hfa ligands coordinated to a barium atom while remaining mononuclear. The compound is a barium bis(hexafluoroacetylacetonate)(18-crown ether-6) complex. The
3.17 crystal structure is shown in Figure
Figure 3. Crystal structure of Barium Bis(hexafluoroacetylacetonate)(18-crown ether-6)
This compound is characterized by having barium coordinated to ten oxygen atoms. Six of the oxygen atoms are from the 1 8-crown-6 ether ring and the remaining four coordination sites are occupied by oxygen atoms from two hfa ligands. The 18-crown-6 and hfa ligands are able to satisfy bariums high coordination number and give
mononuclear complex with two bidentate hfa ligands.
There has been additional research aimed at developing volatile precursors for a variety of heavy alkali earth metals for various solid-state applications. A primary
12 strategy in each case has been to use sterically hindering ligands in association with the heavier alkali earth metals such as magnesium, calcium, strontium, and barium. The
ligand chosen to act as a steric hindrance is a mesityl derivative. Of special interest to this research was the development of Ba{N(SiMe5)2}2. This barium complex is sterically hindered to being only a six coordination species. The main disadvantage with the compounds developed using this technique was the high water and oxygen sensitively the
displayed.18 complexes
Previous research has been done using barium hydride and dimesitylborinic acid
SSP.19 to develop a The dimesitylborinic acid was chosen because of its potential to
sterically hinder the barium atom, while providing a source of boron within the precursor
itself. The goal of this work was the development of a BBO precursor suitable for
MOCVD fabrication of thin films. The product was however unable to be volatilized so
it was concluded that dimesitylborinic acid alone wasn't enough to sterically hinder the
barium atom.1
Building upon previous research and literature references, the proposed precursor
in this thesis is one in which a combination of 18-crown-6 and dimesitylborinic acid are
used together to sterically hinder the barium. The proposed precursor is shown in figure
4.
13 r i
Ba
Figure 4. Proposed single source precursor, barium (18-crown-6) dimesitylborinate
Barium hydride is the barium starting material. It is necessary to use barium hydride due to it acting as a powerful base and being able to react with the proton in dimesitylboronic acid. The ideal ratio would be 1:1:2 of Barium: 18-crown-6:dimesityiborinc acid. This would provide the precursor the necessary ratio of barium: boron required for the formation of BBO.
Experimental:
Materials:
Barium hydride 99.5% was obtained from Alfa Aesar and used as received, and since it is very moisture sensitive, was transferred to a glovebox upon being received and stored under nitrogen gas until ready to be used.
Sigma- 18-Crown-6 99% was obtained from through Aldrich and used as received.
To ensure the reactant remained as free of water as possible it was stored in a glovebox
under nitrogen gas. This precaution was taken due to the observation of older 18-crown-
14 6 losing its crysallinity and liquifying outside the glovebox. This observation was not seen for 18-crown-6 stored under nitrogen gas.
Dimesitylborinic acid 98% was obtained from Sigma-Aldrich and used as
received. It was stored inside of a glovebox under nitrogen gas.
To ensure the above reagents did not become contaminated with any water phosphorus pentoxide was stored inside the glovebox.
THF was obtained from J.T. Baker and stored inside a flammable cabinet until
ready to use. Prior to using, THF was dried over calcium hydride and distilled to a
sealable flask. The flask was fitted with a sealable glass arm that was able to be opened
and closed. After sealing off the flask from the atmosphere the dried THF was
transported to a glovebag and filled with argon. Under this argon atmosphere the
reagents were added to the dry THF and then sealed and transported outside and setup for
a reflux.
Hexane was used to purify the product upon the completion of the reaction.
Hexane was obtained from J.T. Baker and stored inside of a flammable cabinet until
ready to use.
To test the reaction solution thin layer chromatography was employed. Both
normal and reverse-phase TLC plates were tested. Based on the TLC results a column
chromatography system was developed. The packing material used for normal phase was
silica gel, 200-400 mesh. The silica gel was obtained from Sigma-Aldrich and used as
received. The reverse-phase material was Supelclean LC-18. The LC-18 was obtained
from Supelco and used as received.
15 Reaction Scheme: Synthesis of barium (18-crown-6) dimesitylborinate
w Tor
11
Ba o.A >T >.-,r
r? r
/" ^ s BaH2+ +2 oh +-> ;-i. "-+2H
Synthesis of Barium (18-Crown-6) Dimesitylborinate:
A flask of THF over calcium hydride was connected to a condenser which drained
into a fresh round bottom flask. At the end of the condenser a drying tube filled with
Drierite to ensure that the dried THF remained free of water. The fresh round bottom
flask was fitted with a sealable connector to ensure that no water could contaminate the
THF while transferring to the round bottom flask.
Prior to use all glassware was flamed dried using a Bunsen burner to remove any
adsorbed of water. If the glassware would not be used immediately it was stored in an
oven at 1 10 C.
The amount of barium hydride, dimesitylborinic acid (DMBA), and 18-crown-6
(CE) were measured inside of the glovebox under a nitrogen atmosphere. The mole ratio
used in the reaction was 1:1:1 of BaH2:CE:DMBA instead of 1:1:2. The reason for the
16 excess of BaH2 was to ensure that enough pure BaH2 was available for reaction due to possible loss by hydrolysis of this material. Additional CE was also needed to ensure enough was present for the reaction and not lost to side reactions with hydrolyzed BaH2.
Once the amounts of reagents were measured they were sealed inside separate vials and transferred from the glovebox to a glovebag. Argon gas was used to inflate the glovebag.
The reagents were added to the dry THF inside the reaction flask, sealed, and transferred to the benchtop for reflux.
The reaction flask was setup so a positive pressure of argon was present at all times, but not flowing through the flask and removing the refluxing solvent. The reaction flask was attached to a ring stand and fitted with a heating mantle. To the sealable arm a condenser tube was attached. At the top of the condenser tube an argon hose was
connected. The argon line was split so that one end went to the reaction flask and the
other a bubbler containing mineral oil. This ensured that a positive pressure of Argon
was forcing the refluxing solvent to remain inside the reaction flask while still allowing the reflux to occur under a dry, inert atmosphere. An illustration of the apparatus used is
shown in Figure 5.
17 To bubbler
_, Ar
Figure 5. Apparatus design for reaction reflux
The reaction was refluxed at 66 C for 50 hours. In the early reactions a second opening in the reaction flask was fitted with a rubber septum to allow for the removal of
solvent via a syringe. This sample could then be tested via TLC to follow the course of
the reaction. After 50 hours of reflux the reaction showed no further signs of change.
After 2 hours of reflux the solvent started to display a light pink color. As the reaction proceeded the color darkened to a deep purple/maroon color. After 40 hours of reflux the intensity of the color remained unchanged. If the product was left in solvent
18 and exposed to air for more than a few minutes while refluxing the color would slowly disappear and a white precipitate would form. If the solvent were removed and the product was exposed to the atmosphere it would retain its distinctive color and TLC spot,
suggesting it was stable enough to handle in the air.
Testing the reaction by TLC
Once the reaction was completed a small sample was removed and analyzed via
TLC alongside the starting materials. The TLC system used was 1 : 10 THF:hexanes on a
normal phase silica TLC plate. The TLC confirmed the presence of starting materials,
along with a new spot. CE would streak from the origin to have a final Rf value less than
0. 1 . The DMBA had a distinct spot with an Rf value of 0.55. The newly identified
product spot had an Rf value of 0.3.
Two methods were used to identify compounds on the TLC plate. The first was
to use a UV lamp, which would only detect the presence of DMBA. The second method
was to expose the plate to iodine inside a closed beaker. The iodine would stain the TLC
plate so that any compounds present were easily observed. Using this method the CE
was identified, along with the new product spot.
A similar procedure was used when using reverse phase TLC plates were used to
monitor the reaction.
19 Isolation of Barium (18-Crown-6) Dimesitylborate via Recrystalization:
The reaction flask was sealed and transferred to a rotary-evaporator. The
reaction flask was attached to the rotary-evaporator and a vacuum was drawn. Once the
vacuum was established the reaction flask was opened and THF was removed from the reaction flask. The residue left was a purple gel. The reason for it being gel-like is believed to be caused by any un-reacted 18-crown-6 which has a melting point of 38 C.
If the product were left to cool it would harden into a wax like solid.
Once all of the THF was removed the product was washed several times which
hexanes. Both of the starting materials are soluble in hexanes while the product is mildly
soluble. It was found that the best isolation of product occurred when hexanes were
added while the 1 8-crown-6 was melted to ensure a thorough washing. The hexanes
solvent was heated to increase CE and DMBA solubility. The hexanes were separated by
filtering from the washed solid. The filtrate was slowly cooled and evaporated. Upon
cooling a purple solid precipitated out of solution and was collected. If enough hexanes
were evaporated starting material would also precipitate out so the process was watched
very closely. This process was repeated several times to collect several fractions of
isolated product. By recrystalizing the product from hexanes a 6.5% yield was obtained.
Isolation of Barium (18-crown-6) Dimesitylborinate via Column Chromatography:
In addition to recrystalization several experiments were conducted to try to isolate
the product using normal and reverse phase column chromatography. The mobile phase
20 used for normal phase column chromatography was 10: 1 hexanes:THF. Use of this method produced the first successful isolation of product. The drawback to using this method is that the product is not stable enough for all of it to pass through normal phase material and a majority of the product was lost. Only enough product to obtain an NMR spectrum and confirm that no starting materials were present via TLC could be obtained from the column.
Since the product showed poor stability while passing through a normal phase column, a reverse-phase stationary phase was chosen to try to isolate and obtain more of the desired product. The mobile phase used for reverse-phase column chromatography was 20: 1 hexanes:THF. Following the same method as normal-phase column chromatography additional product could be isolated and characterized. However, as for
normal-phase, a large fraction of the product was lost while passing through the column.
While using column chromatography to isolate product did produce enough
samples that could be tested using TLC and NMR, it did not produce enough for
additional tests. The majority of product obtained had to be collected by recrystalization for further testing.
Characterization of Barium (18-crown-6) Dimesitylborinate:
The product was characterized using the following analytical techniques at
Rochester Institute of Technology: Proton NMR using a Bruker, DRX-300, 300 MHz
NMR Spectrometer; IR spectroscopy using a Perkin-Elmer Biorad Excalibur FTIR
FTS3000 with Diffuse Reflectance and ATR; TGA using a TA Instruments TGA 2050;.
Several additional analyses were performed at outside companies.
21 Mass spectroscopy was performed by Thomas C. Jackson and Robert Saccente at
Eastman Kodak Co. The mass spec analysis was negative ion electrospray of product dissolved in THF. The instrument used was a Sciex API365 triple quadrupole mass
spectrometer. The run time was 1 .5 minutes after the sample was loaded into the mass
spectrometer via infusion.
Two samples were sent to Galbraith Laboratories for elemental analysis. The first sample was an initial crop obtained via crystallization. The second sample was the washed filtrate after exposure to air. Elemental analysis for barium, boron, carbon, and
hydrogen were performed on both samples.
Crystal Growth of Barium (18-crown-6) Dimesitylborate:
Growth of crystals suitable for XRD characterizations was attempted. Initial
results were obtained from an undergraduate student, Max Lein, and repeated. The initial
procedure involved taking the THF reaction solution evaporating away a majority of the
solvent. The resulting solution was treated with hexanes and put into cold storage to
induce crystal growth. The resulting crystals were brought to the X-ray crystallography lab at University of Rochester. The crystals grown had lost the distinct purple color and
appeared white.
A second attempt to grow crystals used a similar approach. A sample of solid
product was redissolved in dried THF under an argon atmosphere. To this a thin layer of
hexanes was added slowly. This solution was maintained under a slight flow of argon.
Purple colored crystals were obtained and brought to the X-ray crystallography lab at
University of Rochester. Upon the separation of individual crystals, the crystals would
22 slowly lose their distinct purple color and appear colorless. All attempts to mount and analysis a purple crystal were unsuccessful. The resulting spectrum obtained matched the
original white sample.
Converting Barium (18-crown-6) Dimesitylborate to Beta-Barium Borate:
After isolation and purification of the product it was heated inside of a digitally controlled furnace to induce conversion to Beta-Barium Borate. The heating cycle used is shown in Table V. While heating, a constant flow of oxygen was applied. The reason for the slow initial heating was to remove the organic components from the product without becoming too vigorous.
Table V: Heating Cycle for converting precursor to BBO
Temperature Time
200 C 30 mins
250 C 30 mins
350 C 30 mins
550 C 30 mins
650 C 30 mins
1 800 C 60 mins
23 The three most recent crops that were obtained were heated. Samples were taken from each of the three crops at 550 C and 800 C to measure using powder XRD. Only two temperatures were chosen to collect at to ensure that there was enough sample present.
Preparation of Thin Films of BBO:
A sample of solid product was redissolved in dried THF and spin coated onto a
sapphire wafer. The wafer was supplied by valley, and was a material r-plane sapphire
with a 100 mm diameter and 0.5 mm thickness. Both sides were optically polished for
enhanced thin film deposition. The substrate was spun at 500 rpm for 60 seconds, with
an acceleration and deceleration of 100 rpm. The coated substrate was then submitted to
Tom Blanton at Eastman Kodak Research Laboratories, where it was baked in a DelTech
furnace for 5 minutes at 300, 400, 500, 550, 600, 650, and 700 C. After each heat
treatment the substrate was allowed to cool to room temperature and analyzed via XRD.
The substrate was also analyzed prior to heat treatment.
Results and Discussion:
Confirmation of Isolation:
When the product was isolated by column chromatography and recrystalization it
yielded a single spot TLC on both normal and reverse phase plates. The desired precursor was not expected to have any color, but instead be white. The purple color also only appeared under anhydrous conditions when barium hydride, 18-crown-6, and
24 dimesitylborinic acid were refluxed. If any of the reagents were missing a color did not
appear.
Confirmation of Barium and Boron in Barium (18-crown-6) Dimesitylborinate:
Once the product was isolated and confirmed to be pure it was tested to determine
that it contained both barium and boron. Initial confirmation was done via combustion of
product. When the product was ignited in a flame it produced a bright green color signifying the presence of boron. After the product was combusted a white residue was left. To ensure that the white residue left was indeed due to the presence of barium and not any organics it was loaded into a crucible and heated for upwards of 30 minutes while
the crucible was red hot. After this time the presence of a white solid metal oxide
signified the presence of barium metal in the pure product.
Identification of Coloration:
Previous research in the development of BBO precursors reported only colorless precursors expected for Ba(2+) compounds. The fact that this reaction (Reaction Scheme on page 16), yielded a reproducible purple product was unexpected. This purple product
retained its coloration in the solid state and gave a single spot in the TLC and if it were added to water or a solvent with water present it lost its color. The most likely possibilities to consider are that the desired precursor was obtained and it unexpectedly had a purple color, or, alternatively the purple coloration was the result of the formation of a byproduct, which rearranged on the TLC plate to match the single spot. It is also a
25 possibility that the purple byproduct was only present in small amounts and insoluble in
the TLC solvent, and thus would not be present on the TLC plate.
Barium has shown that it is capable of reacting with dialuric acid to form a white
salt. When this salt is oxidized in air the dialuric acid is converted to alloxantine, which
barium.20 forms a purple salt with
Reaction Scheme: Formation of barium dialuric acid salt.
oo y HN^NH ""A V- 0 J 0=( 0 Ba < )=0
Ba(OH)2 + oh ^ o o +2H20
Reaction Scheme: Formation of barium alloxantine salt
o o HN V V-NH
HN^ 0 >~NH O | O
Ba
O 0 0 0
HN / HN V \ HO NH \ Q NH
o' o' o "o Ba(OH)2 + -> +2H20
This reaction is widely used in biochemical fields as a way to identify two pyrimidines,
uracil.21 cytosine and It is possible that barium dimesitylborinate underwent an
analogous reaction (oxidation) to produce a purple byproduct.
26 Additionally, barium has been shown to form a red colored product when reacted
residue." with sodium rhodizonate. This reaction is a common test for gunpowder This reaction parallels that of the dialuric acid reaction in that the resulting product is barium coordinated to a six-membered ring through an oxygen bond.
Reaction Scheme: Formation of barium rhodizonate
o o
\ Ba
BaCl2+ - +2NaCl
If the purple coloration were due to a side reaction it would most likely involve
Dimesitylborinate ligand being heated for an extended period of time. This side reaction would require anhydrous conditions and would only occur in the presence of barium hydride, 18-crown-6, and dimesitylborinic acid. This unexpected byproduct must either
rearrange on both a normal phase and reverse phase TLC plate with the major product giving a single spot in both TLCs, or be only present in trace amounts and insoluble in
TLC solvent.
Single crystal structure of Hydrolyzed Barium (18-crown-6) Dimesitylborinate:
The crystal structure of the hydrolyzed product of barium ( 1 8-crown-6)
Dimesitylborinate, C3o08H55B, is shown in Figure 6. The arrangement of each molecule
as arranged in the entire crystal structure is shown in Figure 7. The structure shows a
27 water molecule inserted inside of 18-crown-6 with a neighboring dimesitylborinic acid.
The bond lengths and angles are collected in Table VI.
Table VI. X-ray crystallography data for hydrolyzed product C3o08H55B
D-H....A d(D-H) D(H....A) d(D...A) <(DHA)
01-H10...02 0.870(17) 1.853(17) 2.7199(11) 174.0(16)
02-H201...04 0.857(18) 1.985(18) 2.8306(14) 168.8(15)
02-H201...0C 0.857(18) 2.24(2) 3.074(9) 162.8(15)
02-H201...05v 0.857(18) 2.495(18) 3.087(6) 127.0(13)
02-H202...08 0.855(19) 2.034(19) 2.8696(11) 165.3(16)
The molecular interactions holding this product together involve hydrogen
bonding between the oxygen of the water and the proton from dimesitylborinic acid. In
addition there appears to be hydrogen bonding between the protons of the water and
oxygen atoms in the 18-crown-6, most noticeably between the water hydrogen atoms
H201 and H202 with the CE oxygen atoms 04 and 08, respectively.
It appears as if one of the protons, labeled H201, is slightly closer to the 18-crown-6, than the other, labeled H202.
28 Figure 6. Crystal structure of hydrolyzed product C3o08H55B
Figure 7. Molecular view of hydrolyzed products C3o08H55B crystal structure
29 Characterization of Barium (18-crown-6) Dimesitylborinate via Infrared
Spectroscopy:
The IR spectra of the DMBA, CE, and the product are shown in Figures 8-10.
There are several significant shifts between free CE and product indicating the CE is
cm"1 present and coordinated. The region between 2700 and 3000 represents the
stretching between the C-H bonds. There is a distinct change in this region upon complexation. There is a significant loss of intensity and definition once the 18-crown-6
is coordinated compared to free 18-crown-6. There is also a significant shift from
cm"1 2893/2849 to 2904/2864 cm"1. The second, more dramatic shift, occurs at 1 123 and
1 103 cm"1, due to the C-O-C stretching bands. In free 18-crown-6 there are 2 distinct
cm"1 peaks, but in the coordinated product the peak at 1 123 is no longer visible and the
cm"1 peak at 1 103 shifts slightly to 1099 cm'1. There is also a distinct change around
1041 cm"1. In free 18-crown-6 there are 3 distinct peaks at 1075, 1057, and 1041 cm"1.
However, in the coordinated product there is one broad asymmetrical peak at 1041 cm"1.
This confirms that 18-crown-6 is present in the product and has changed significantly from free 18-crown-6, most likely due to complexation.
When comparing DMBA to the product the most noticeable change occurs between 2900 and 3500 cm"1. There are several distinct peaks in pure DMBA at 3500,
3271, 2968, 2914, and 2850 cm'1. However, the product has no distinct peaks in this
cm"1 region. The only significant peak is a slight shift at 3491 which creates a shoulder.
This region is attributed to O-H stretching. The fact that there are peaks below the
normal CO-H observable region is believed to be because the material is BO-H instead.
30 The reason for still seeing BO-H peaks in the isolated product could be caused by hydrolysis after isolation. However, there are no distinct water peaks associated with the products spectrum, indicating that at the time of analysis the product was mostly free from water.
31 S
.o ^^Sv aaueHiiusuejj.% Figure 8. IR spectrum of Dimesitylborinic acid 32 p 58 as *8 18 li*. .*# 1 I si 155 -, a" , i i a a * WBPHU9UBJJ_% Figure 9. IR spectrum of 18-crown-6 33 Mt - 85, * '6 is " I - -I r 4 *->t-3 83UeUjUlflUKJl% Figure 10. IR spectrum of barium ( 18-crown-6) dimesitylborinate 34 Characterization of Barium (18-crown-6) Dimesitylborinate via Nuclear Magnetic Resonance: With the confirmation that the isolated product contained barium and boron, samples of product, DMBA, and CE were analyzed by NMR. The solvent used was deuterated chloroform. The spectra for solvent, DMBA, CE, product isolated by column chromatography, and product isolated from hexanes can be seen in Figures 11-15. A comparison of the observed peaks for the product, dimesitylboronic acid, and 18-crown-6 is shown in Table VII. For the sample isolated by column chromatography the integration for each peak observed for A:B:CE was 2.4 : 1.0 : 3.1, compared to the expected ratio of 4.5 : 1.0 : 3.0 (18:4: 12); where A represents the methyl hydrogen atoms, B represents the hydrogen atoms on the benzene ring, and CE represents the hydrogen atoms on the CE. It is surprising that the peak corresponding to the mesityl methyl hydrogen atoms is so low compared to the hydrogen on the benzene ring. It is possible that certain peaks for the mesityl methyl hydrogen atoms were shifted and obscured by the solvent peak, or broadened out due to slow molecular motion. The ratio between CE and those on the benzene ring show the expected ratio. For the sample isolated by crystallization from hexanes the observed integration for A:B:C:CE is 17.6 : 3.8 : 1.0: 13.0, compared to the expected integration of 18:4:1:12, where C represents the hydroxy proton from DMBA. The integration for A:B:CE is 4.6 : 1.0 : 3.4 compared to the expected integration of 4.5 : 1.0 : 3.0. This sample also shows a ratio of two dimesitylborinates to one 18-crown-6. The presence of the hydroxy proton suggests that this sample underwent hydrolysis. However, if the sample were 35 pure, as TLC suggested, then the integrations should still reflect the components that were present in the precursor. It is interesting to note that the water present in solvent shows the same shift as water present in both samples. It would be expected that the hydrolyzed product identified by x-ray crystallography would show a different shift for the water peak. However, the water peak is noticeable broader in both spectra, suggesting that the water may be exchanging or that the dimesityborinate-water-CE complex is in equilibrium in solution. Of special interest is the noticeable shift in CE in both samples. This suggests that the crown ether is coordinated. In figure 14 the hydrogen from the mesityl methyl show drastic changes concerning split patterns, as well as those on the benzene ring compared to the starting material. The sample in Figure 15 also shows a different splitting pattern for the methyl groups as well as the benzene hydrogens. The fact that the splitting patterns are not symmetrical suggest that the product is sterically hindered in such a way as to create different environments for each specific hydrogen. The sample obtained from column chromatography differs from the sample obtained from hexanes. It is likely that the original precursor rearranged while passing through the column resulting in a poorer sample for NMR analysis. It still, however, confirms the presence of one 18-crown-6 for two dimesitylborinates. The sample obtained from hexanes shows some hydrocarbon interference, most likely from residue hexane. The fact that the two samples obtained show the same ratio of 18:crown-6 to dimesitylborinate strongly suggests the correct ratio(4.5: 1:3.0) has been obtained for the desired precursor. 36 !gg < va o a *<3 ,*j >i a .-< a o H o 01 O. m in a id vo-J 01 ft va O h w s y -.(;-; 11. ._( siess 5 i O w o* 12 9g: feu is. 3: III I 80 91 7\ iLZ I- A~ Ufl- u ess'o- t e Figure 1 1 : NMR Spectrum of D-chloroform 37 111! djIlUuiBiHWfl ii^i ibis JU^iIs ^j_ s ^n.. L c& ^H/" Figure 12: NMR spectrum of dimesitylborinic acid 38 i aI iI US e I a Bljibil if" ||5ir-iriliiisil SaJ?| fq-ra mm 1 iSil cSJlKBeiinlissaae^ Hs2i cd*fifiaK aaSclcfS vi UJ L_ O iesja \a \- Figure 13. NMR spectrum of 18-crown 39 i SLl lei a S a iisfeli r fpi^iriiiiPii"* |5 Is * xm 9 a f- . 1 9 lill iillf.!i! laassesa /i a> 1 .f ttt> -f V) Figure 14. NMR spectrum on Barium (18-crown-6) Dimesitylborinate obtained from column chromatography 40 c_ x a. re 0,3 "-i 100 3 -a S*' o -< o IOOS6; W. > 3 tJ a. u-CE-i-.=.ct-MzaKfc.ca;SQe-.Q 5 a. a.w cl, e s&: 3S tjj lk. & ci- i a ^- 0 9901 HO '9 cO = Of.9'0 J^ D ^ V* S6f0- XPIB93UI Figure 15: NMR spectrum of Barium (18-crown-6) Dimesitylborinate obtained from hexanes 41 Table VII: NMR data comparing starting materials to product Proton A B C CE H20 CDC13 1.55 18-crown-6 3.7 Dimesitylborinic 2.20 6.75 5.85 acid Product isolated 2.20 6.75/6.15 3.45 1.55 by column chromatography Product isolated 2.20 6.80/6.75 5.85 3.60 1.55 from hexanes Shift 0.0 0.0/0.6 0.25 Integration of 2.4 1.0 0.0 3.1 product isolated by column chromatography* Integration of 17.6 3.8 1.0 13.0 product isolated from hexanes including the hydroxy proton* Integration of 4.6 1.0 3.4 product isolated from hexanes excluding the hydroxy proton* Expected 4.5(18.0) 1.0(4.0) 0.0(1.0) 3.0(12.0) Integration of product** / integrations were determined b) measuring the, length of pea cs 42 Characterization of Barium (18-crown-6) Dimesitylborinate via Thermogravimetric Analysis (TGA): Air was passed over the sample while heating to ensure an ample supply of oxygen to remove any organics and for the conversion to beta-barium borate. The scan obtained is shown in Figure 16. Observable weight loss begins to occur around 1 16 C. The first decomposition event occurs at 239 C and leaves 55.94% of the compound remaining. This corresponds to four mesityl groups being removed from the product. The second decomposition event occurs at 305 C and leaves 30.02% of the product. This corresponds to the loss of 1 8-crown-6 from the remaining sample after the loss of four dimesityl groups. The weight loss stops at 667 C with a weight residue of 23.36%, corresponding to the conversion of the precursor to beta-barium borate. The TGA data supports the NMR data for the proposed SSP formulation Ba(18-crown- 6){OB(Mesityl)2}2. 43 o < (- -o CO 00 o LU o d > LU 0. co < "* > t- co ID co> o < < CD 8p > u 1 o o -o CD O gQ jj (D c o < O * -O CO 1_ CD Q. E CD I- o -o CD Q LU o > CD CO ^ 00 1 o o o o o o CD CD X> "3- o CO CD CM "5... o CNJ TO N CO CO 2 (%) W6i9/\A Figure 16. TGA Scan of Barium (18-crown-6) Dimesitylborate 44 Characterization of Barium (18-crown-6) Dimesitylborinate by Elemental Analysis: Two samples were sent to Galbraith laboratories to determine the elemental analysis of the product. The first sample was recrystalized from hexanes that were used to wash the solid product once the reaction was done (filtrant). The second sample was the washed solid product which had changed from purple to brown over time (filtrate). Both had similar TLC spots. The results of the elemental analysis can be seen in Table VIII. Table VIII. Elemental Analysis of Barium ( 1 8-crown-6) Dimesitylborinate Compound Ba% B% o% C% H% Expected 14.7 2.3 13.7 61.8 7.2 compound Sample 1 15.3 2.3 41.14 36.62 4.64 Sample 2 14.0 3.68 26.15 49.55 6.62 Water 0.0 0.0 88.9 0.0 11.1 1 8-crown-6 0.0 0.0 36.2 54.3 9.5 Dimesitylborinic 0.0 4.1 6.0 81.5 8.4 acid Hydrolyzed 0.0 2.0 23.4 65.7 8.9 product Barium Hydride 98.6 0.0 0.0 0.0 1.4 Barium Hydroxide 80.1 0.0 18.7 0.0 1.2 Ba (DMBA)OH 33.0 2.6 7.6 51.3 5.5 45 By comparing the percentage of barium and boron the product appears to have two dimesityl borates for every one barium, agreeing with the theoretical compound. What is unexpected is the percentage of carbon and oxygen present. There is significantly more oxygen present than expected, as well as significantly less carbon. The most likely impurity that would cause such a drastic increase in only oxygen would be water. However, is such a large amount of water were present, it should lower the amount of barium and boron observed. One factor that could be relevant is that different analysis were done for four out of the five elements. Both barium and boron were analyzed by ICP. Carbon and hydrogen were analyzed by combustion. It is more likely that the analysis of barium and boron by ICP is more accurate than the analysis of hydrogen and carbon by combustion. It is possible that the combustion of product was incomplete. This would account for a lower amount of observed carbon and hydrogen. Since carbon and hydrogen are lowered, the amount of oxygen inferred would be higher than expected, which is observed. Alternatively, if the sample analyzed were a mixture of product and hydrolyzed product that would still not account for the abundance of oxygen nor the low of carbon analysis observed. The fact that two analysis by ICP on two separate samples show the expected amounts of barium and boron present in the target SSP supports the proposed formulation of the product. The fact that the carbon and hydrogen reported percentages are so low 46 and so different from the two samples suggest an incomplete combustion occurred, resulting in an inaccurate results. The elemental analysis shows a ratio between barium and boron of 1 Vindicating that the ratio between barium and boron is the desired amount. Based on the NMR data, the ratio of dimesityl groups to those of 18-crown-6 was 4:1, indicating that there were two dimesityl borates for every one 18-crown-6. This is further supported by the weight loss events there were observed by TGA. By combining the three sets of data, the product appears to have a ratio of 1: 1:2 for Ba : 18-crown-6 : Dimesityl borates. This agrees with the proposed structure of the product, as shown in Figure 4. Characterization of Barium (18-crown-6) Dimesitylborinate via Mass Spec: Samples sent to Eastman Kodak Co., Inc. were analyzed via Negative Ion Electrospray to obtain a mass spectrum. The mass spectrum is shown in Figure 17. The expected product would have a molecular weight of 932 g/mole. No peak was observed matching this weight. However, there were several peaks that are attributed to specific components of the desired complex. The first peak of interest occurs at 796.8 m/z. This peak is unusual due to it corresponding to an 18-crown-6 coordinated with two dimesitylborinic acids and a proton. The isotopic pattern observed is consistent with a compound containing two boron atoms. It appears that the product was too unstable for mass spectral analysis and decomposed, with the barium atom was displaced by a proton. The next peak of interest occurs at 53 1 .7 m/z. This peak corresponds to a single dimesityl coordinated to an 18-crown-6 with a proton. This supports the argument that 47 the product is too unstable to observe, and is decomposing, with the barium being displaced by a proton. This shows that the product can undergo further destabilization by losing a dimesitylborinic acid group. The isotopic pattern observed is consistent with a compound containing a single boron atom. The third peak of interest occurs at 421.4 m/z. This peak correspond to a barium bonded to one dimesityl borate and a hydroxyl group. Based on crystal structures it is believed water is capable of displacing the barium along with one dimesityl borate. This peak corresponds to the barium byproduct which is formed which only has one dimesityl borate group. What is unusual is the fact that based on the mass spec data the barium is still mononuclear despite the absence of a second dimesityl borate and 18-crown-6 to act as a steric hindrance. It is interesting to note that there were no peaks observed occurring above 932 m/v. Considering this, along side the data suggesting the displacement of barium from the product, it is feasible to consider that this product is indeed mononuclear. If there were multiple barium atoms, and they were held together with covalent bridging groups, it would be more difficult for the product to fall apart as observed. 48 & 8 g I? & ^ 5 6 CD '3 co 0 CM co CM CO ,_ 8 C\J ' I ' 1-1 ' "A 5 COOOOOCOOOSNNNNNNNNNNNNNNNNNCD &2 2 8$8$8&8&8$8$8&8$8$88 T^i^^^^aioiobcxiSKcDCDLriio^^cocdcvicvi-r^-r^Lri Intensity, cps Figure 17. Mass Spec of barium (18-crown-6) dimesitylborinate 49 X-ray Diffraction of Heated Powders: Three samples were heated to 800 C to observe the conversion to beta-barium borate. The first sample chosen was the initial precipitate recrystalized from hexanes, while the second sample chosen was the second precipitate recrystalized hexanes. The third sample had changed colors to being purple brownish since being exposed to the atmosphere. The first and third samples were also submitted for elemental analysis results. All three samples had similar TLC patterns. The X-ray diffraction results were measured each sample at 550 C and 800 C, for a total of 6 spectra. The two spectra for the first sample are shown in Figures 18, 19. The spectra for the second sample are shown in figures 20, 21. The samples for the third sample are shown in figures 22, 23. X-ray Diffraction of Thin Film: The XRD spectrum of the baked thin film is shown in Figure 24. The XRD spectrum does not show a match for any known BBO phase. However, it is apparent that a new, undetermined phase, is identified. It is possible the precursor was unable to convert to the beta form of BBO if a majority of the product had undergone hydrolysis, resulting in an incorrect ratio of barium to boron. The resulting boron deficient precursor could account for the new peak. 50 (SdD)*l|SU*ul Figure 18. Initial Product Crop Heated to 550 C 51 (SdO)xl,s,J*lul Figure 19. Initial Product Crop Heated to 800 C 52 (Sd0)*l'su*iui Figure 20. Second Product Crop Heated to 550 C 53 (Sd0)*l'su3iui Figure 2 1 . Second Product Crop Heated to 800 C 54 (SdOM*"3!"! Figure 22. Washed Product Residue Heated to 550 C 55 (SdD)*l,SU*lul Figure 23: Washed Product Residue Heated to 800 C 56 q I i O i i i i O 'O CD DOOlDO_Ci o "cTngnCTTITTD TT^ CD QD CD iXl CQ ". , CD CD " |||| :. u_ u_ L_ iZ iT iZ . iZ ;:. O CD CD CD o o CD CM CM CM r j CM CM "1 CM i '- _ 1 _J_ ry) CO CO CO CO CO . CO h- h- f :':: fr g: m CT3 03 TO CO (TJ (Tj O O O O O CD '. O ^" i_i O i_i U.i o o r- ,-sj co ^r in lij to cq < < < < < -^ < _ 00 cm cm cm cm cm cm rt- CQ L'J C'J i. 'j CQ . CQ 0> QJ Cu LU CO 03 CO CD " ^ J ^ ^ ' Q. CO 3 Q II CO (SdO)^I!SU9lul Figure 24. XRD Thin films on sapphire substrate 57 Conclusions: A novel BBO precursor, Ba(18-crown-6)(OB(Mesityl)2)2 has been synthesized and shown by x-ray diffraction to decompose to beta barium borate starting at 550 C. The precursor has been shown to be highly susceptible to hydrolysis in which the barium atom is displaced by a water molecule. This made it difficult to ensure the purity of the sample when performing chemical and spectroscopic analysis. However, when looking at all the data together certain trends appear. Two samples obtained by different techniques that had a single spot TLC and both showed an NMR ratio of 1:2 for 18- crown-6 to DMBA. This ratio is supported by TGA results that show the precursor decomposing to form a barium residue consistent with BaB2Ozi, and where each step is accounted for with a loss of 4 mesityl groups and the 18-crown-6 ring. In addition, both the mass spec results suggest that the precursor is mononuclear. The samples submitted for elemental analysis had the same single spot TLC, and showed the correct atomic ratio of barium to boron of 1:2. Taken together the data suggests a precursor was produced with the desired properties of having a mononuclear barium complexed with 18-crown-6 and containing two dimesitylborate groups. A minor purple-colored byproduct, probably from oxidation, was formed concurrently. The project goal for this precursor was to use it to prepare BBO films by MOCVD. While this precursor is too unstable in a non-anhydrous system for this goal. There are two volatization, significant progress has been made towards complex suitable for MOCVD. The one extreme extremes considered when designing a is that the compound is too stable and will not volatilize, but rather eventually decomposes into BBO. The other extreme is that the compound is too unstable, and will 58 decompose before volatilizing. Previous research involving barium dimesityl borates has suggested the former. This new precursor, however, appears to be better described by the later. While this precursor is not itself applicable to MOCVD, it shows significant progress towards the development such a precursor. Of special interest is the noted development of a new barium borate crystalline phase at temperatures exceeding 550 C. Based on the sample used it is highly possible that this new crystalline phase was the result of the hydrolyzed barium byproduct. This would account for a ratio of 1 : 1 for barium: boron, which would result in a boron- deficient product. Future work: A significant disadvantage involving this precursor was using barium hydride as the barium source. Barium hydride was used because it acts as a strong base, capable of reacting with the hydrogen from dimesitylborinic acid. There was a large amount of material. both uncertainty regarding the purity the barium hydride starting Since the barium hydride starting material and product were very moisture sensitive ensuring that the entire reaction, product isolation, and purification steps proceeded under anhydrous conditions was a daunting task. The next step towards developing a more efficient precursor must address the hydrophilic nature of barium. Current research is being conducted as a follow up using barium hydroxide as the compound. Barium hydroxide suitable barium source and using a para-boron phenol is because it can react with a proton from a phenol group, which is significantly more acidic compared to the weak acid DMBA. This addresses the primary concern of needing to 59 remove water for the initial reaction of the precursor. Whether the phenol group will be sterically hindering enough is yet to be determined. In addition the hydrolyzed product appears promising. Additional research could be done to purposefully synthesize, purify, and characterize the compound. Any additional properties of interest could be determined and recorded. Also of interest is the analysis and characterization of the new barium borate crystalline phase observed. Since this crystal phase was obtained via the hydrolyzed barium by-product it should be easily reproduced under controlled conditions. Whether this crystalline phase exhibits any suitable NLO properties remains to be determine. 60 References 1. Rajan, Malika. "Global market for non-linear optical materials to reach $1.66 2009." billion by Business Communications Company, Inc. bccresearch.com/editors/RGB- 1 17N/html 2. Studebaker, D. B.; Stauf, G. T.; Baum, T.H. "Second harmonic generation from beta barium borate (BaB204.) thin films grown by metalorganic chemical deposition" vapor Appl. Phys. Lett., 1997, 70 (05), 565-567 3. Fujian Castech Crystals, Inc. www.castech.com. Last Accessed 9/5/06 optics" 4. 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