Copper, Silver, and Gold Clusters: a Synthetic and Structural Investigation

COPPER, SILVER, AND GOLD CLUSTERS: A SYNTHETIC AND STRUCTURAL INVESTIGATION

A thesis submitted to the Kent State University Honors College in partial fulfillment of the requirements for University Honors

Harrison Olivia Davis

May, 2019

Thesis written by

Harrison Olivia Davis

Approved by

______, Advisor

______, Chair, Department of Chemistry and Biochemistry

Accepted by

______, Dean, Honors College

TABLE OF CONTENTS:

LIST OF FIGURES……………………………………………………………………….iv

LIST OF TABLES…………………………………………………………………..…….v

ACKNOWLEDGEMENTS………………………………………………………...…….vi

CHAPTERS:

I. INTRODUCTION

II. SYNTHESIS OF COPPER, SILVER, AND GOLD COMPLEXES

III. NANOMATERIAL SYNTHESIS AND CHARACTERIZATION

IV. CONCLUSIONS

REFERENCES……………….…………………………………………………..…….41

iii

LIST OF FIGURES

Figure 1. Bridging ligands present in complexes 1-5 ...... 2

Figure 2. Thermal ellipsoid plot of 1. Ellipsoids are drawn at 30 % level. H atoms have been omitted for clarity...... 27

Figure 3. Thermal ellipsoid plot of 2. Ellipsoids are drawn at 30 % level. H atoms have been omitted for clarity...... 28

Figure 4. Thermal ellipsoid plot of 3. Ellipsoids are drawn at 30 % level. H atoms have been omitted for clarity...... 29

Figure 5. Thermal ellipsoid plot of 4. Ellipsoids are drawn at 30 % level. H atoms have been omitted for clarity...... 30

Figure 6. Thermal ellipsoid plot of 5. Ellipsoids are drawn at 30% level. H atoms have been omitted for clarity...... 31

Figure 7. UV-VIS spectra of Cu2O Nanocrystals ...... 34

Figure 8. TEM image of Cu2O Nanocrystals ...... 35

Figure 9. TEM image of Cu2O Nanocrystals ...... 36

Figure 10. TEM image of Cu2O Nanocrystals ...... 37

Figure 11. TEM Image of Cu2O Nanocrystals ...... 38

LIST OF TABLES:

Table 1. Data Collection Parameters for 1 – 3.38 ...... 21

Table 2. Data Collection Parameters for 4 – 5...... 22

Table 3. Selected inter-atomic distances (Å) and angles (º) for 1-2...... 23

Table 4. Selected inter-atomic distances (Å) and angles (º) for 3 ...... 24

Table 5. Selected inter-atomic distances (Å) and angles (º) for 4 - 5...... 25

Table 6. Metal – Metal Interatomic Distances for 1-5 compared with literature values ...26

ACKNOWLEDGEMENTS

I would like to thank Dr. Scott Bunge for his patience and guidance through the process. I would also like to thank the current and former members of the Bunge research lab, especially to Alex Ocana and Joshua Hollett for their help over the years. Also, I would like to thank my parents for their support. Finally, I would like to thank the members of the defense committee for their time.

CHAPTER I

INTRODUCTION

Group 11 metals (Cu, Ag and Au) have played a prominent role in the fields of organic synthesis, medicinal chemistry, and nanomaterials over the past few decades.1,2,3,4,5

With respect to nanomaterials, this can be attributed to copper, silver and gold possessing unique size- and morphology-dependent properties.6,7 For example, often utilized in the healthcare industry, group 11 nanocrystals are regarded for their anti-microbial, anti- inflammatory and anti-neoplastic properties.8,9,10 Their morphologies can come in the forms of nanorods, nanowires, twinned nanocrystals, nanoflowers, nanoprisms, nanospheres, and nanocubes.9,11,12,13 Novel copper, silver and gold molecular complexes often serve as precursors for the nanocrystal synthesis. The nanocrystal size and shape are primarily controlled via the metal precursors chosen and the reaction conditions in which the synthesis is carried out.14

Although a wide variety of reaction conditions have been explored in regard to nanocrystal synthesis, the ability of various inorganic complexes to serve as precursors has been investigated to a lesser degree. Therefore, the major focus of this project was to synthesize unique copper, silver, and gold precursors with a sterically varied group of ligands. The synthesis and characterization of five novel amido compounds will be described herein (Chapter II). Among these complexes, there are five district ligand types.

Figure 1 enumerates each of the ligands and additionally denotes which complex (1-5) contains which ligand.

Figure 1. Bridging ligands present in complexes 1-5

Despite nitrogen being formally considered a hard base according to hard-soft acid-base

(HSAB) theory, the amido ligands shown in Figure 1 are regarded for being capable of facilitating the isolation of well-defined metal centers with varying levels of Lewis acidity.15,16,17 The amido ligands enumerated above are additionally capable of bridging between metal centers.17 Cu (I), Ag (I), and Au (I) are generally regarded as soft Lewis acids and typically form reactive unstable complexes with amido ligands. This can sometimes play a challenging role in the synthesis and isolation of these compounds. In addition to their low solubility of the precursor salts, additional limitations in the forms of light, heat, and moisture sensitivity exist for these complexes; they readily undergo reduction to the metal. Despite these limitations, several group 11 amido complexes have been previously synthesized.

The general synthesis of the group 11 bis(trimethylsilyl)amides, [M{μ-

N(SiMe3)2}]4 (M = Cu, Ag and Au), can be traced back to 1964 when the first copper

18 complex, [Cu{μ-N(SiMe3)2}]4, was originally reported by Bürger and Wannagat. In this

report, only the synthesis and spectroscopic characterization of the product was reported.

The crystal structure confirming the nuclearity of the structure was reported later in 1998 by Maverick.19 The synthetic effort was then extended down the group by Lappert et. al.

20 with the synthesis and structural characterization of [Ag{μ-N(SiMe3)2}]4 in 1996.

Finally, the first base-free gold amide, [Au{μ-N(SiMe3)2}]4 was reported by Rees and co- workers in 2000.21 The isolation of these complexes allowed the previous pre-conceived notion regarding the capability of isolating such concepts to be questioned. Thus, leading to new directions in which the group 11 amido complexes may be explored.

Scheme 1: General synthesis of group 11 tetranuclear bis(trimethylsilyl)amides18,19

In 2008, Bunge and co-workers reported the use of the 1,1,3,3-tetraalkylguanidinate in conjunction with bis(trimethylsilyl)amide to isolate Cu, Ag, and Au clusters.22 Lithium

1,1,3,3-tetraalkylguanidinate (LiTAG) clusters were originally reported by Wade et al.23,24

The lithium dimethyl diethylguanidinate guanidinate synthesis in described in Scheme 2.

Scheme 2: Synthesis of [Li{N=C(NMe2)(NEt2)}]

This ligand was utilized in conjunction with bis(trimethylsilyl)amide in order to achieve the isolation of novel Cu, Ag, Au, clusters. Similar to the complexes described by

Bunge, Chapter II details the isolation of a similar compound (3) in which

[Li{N=C(NMe2)(NEt2)}] and [Li{N(SiMe2Ph)2}] are reacted with CuCl to generate a tetranuclear complex. The lithium amide, Li[N(SiMe2Ph)2], is generated by deprotonation of the corresponding amine with n-butyllithium and isolated as a crystalline solid. (Scheme

3) This lithium amide was used further to isolate complexes 3-5 described in Chapter II.

25 Scheme 3. Synthesis of Li[N(SiMe2Ph)2]

The two additional phenyl groups (versus the bistrimethylsilylamide) introduce bulkiness and a greater steric hinderance. This ultimately affects the metal-metal interatomic distances within the clusters which will be later discussed in Chapter 2. The influence of these steric groups was further investigated in the paper entitled “Tri- and

“ tetrameric copper(I) amides [Cu{N(SiMePh2)2}]3 and [Cu{N(SiMe2Ph)2}]4 by Power and co-workers. This paper discussed the result of introducing phenyl groups to each ligand.

This resulted in steric hindrance to the point that the complex contained only three Cu metal centers rather than the four metal centers present in the bis(dimethylphenylsilyl)amide.26

26 While [{Cu[μ-N(SiPhMe2)2]}4] has been previously synthesized and characterized, the

Ag and Au analogs have not been previously isolated.26 Chapter II will discuss their synthesis. Examples include use in catalysis especially for CO oxidation, precursors for nanoparticles, and luminescent materials27,28,29,19,7.

Despite the challenges associated with synthesizing these complexes, group 11 metal complexes have been utilized in several applications. The use of metal silylamido complexes have proven themselves useful for grafting onto mesoporous silica for use as a catalyst in a variety of reactions.30 Gajan et al. reported the use of a trimethylsilylamide Au

(I) complex, {Au[N(SiMe3)2]}4 which served as a precursor to gold nanoparticles. The Au complex was then grafted onto a mesoporous silica surface and reduced under H2 in order to form 1.8 nm gold nanoparticles thus enhancing their intrinsic catalytic and oxidative activity.30

With amido ligands bridging between the metal centers, a number of unique oligomeric clusters have been synthesized. Investigation into the metal-metal bond

distances in these clusters has resulted in obtaining further insight into the nature of bonding interaction between group 11 metals.31 These d10-d10 metal complexes exist in clusters which possess short metal-metal bond distances28 thus making them attractive from a nanocrystal precursor standpoint.32

The ability of inorganic Cu (I), Ag (I), and Au (I) clusters to be nucleated and injected into a long-chain amine at high temperatures has been previously reported to result in the nucleation, and growth of metal nanocrystals.33 N,N-Dimethylhexadecylamine

(HDA) was determined to be the long chain amine of choice for this investigation and serves as both a capping agent and coordinating solvent. It’s ability to solubilize metal salts as well as stabilize them in solution34 is additionally an attractive feature. Scheme 4 outlines the general procedure carried out in order to achieve the nanocrystals reported herein.

Scheme 4: Nanocrystal synthesis

The use of silylamides in inorganic copper nanocrystal precursors is ideal due to their susceptibility to oxidation and reduction as well as the ease at which metathesis reactions can occur for these compounds.35

In summary, Chapter II describes the synthesis and characterization of copper, silver, and gold complexes, while Chapter III explores the nanocrystal synthesis via Cu(I) precursors. The structures of the complexes have been confirmed by x-ray crystallography,

multi-nuclear NMR, FT-IR, melting point (decomposition) and CHN elemental analysis.

The synthesis of nanocrystals was confirmed via characterization with UV-VIS spectrophotometry and Transmission Electron Microscopy (TEM).

CHAPTER II

SYNTHESIS OF COPPER, SILVER, AND GOLD COMPLEXES

Introduction:

Low coordinate metal amido complexes play a major role in the field of inorganic chemistry due to their industrial applications as well as the insight they provide into the properties of metal clusters.17,36 The scope of this chapter focuses on the synthesis and structural characterization of Cu(I), Ag(I) and Au(I) amido complexes (See Figure 1).

While interesting and full of potential, these complexes are often difficult to synthesize and are subject to many opposing forces which threaten their isolation (such as air, moisture, light, and temperature). Despite these challenges, this chapter describes the successful synthesis, crystallization, and characterization of five unique complexes: [Cu2(μ-NMe2){µ-

N(SiMe3)2}]2 (1), [Cu2(µ-N=C(Ph)(NMe2){µ-N(SiMe3)2}]2 (2), [Cu2{µ-

N=C(NMe2)(NEt2)}{µ-N(SiPhMe2)2}]2 (3), [Ag{μ-N(SiPhMe2)2}]4 (4), and [Au{μ-

N(SiPhMe2)2}]4 (5).

Experimental

Due to the sensitive nature of this chemistry, the reactions were carried out under an inert atmosphere of argon. Along with the use of glove box techniques to prevent the presence of air or water, light exposure and temperature were also carefully controlled. The following chemicals were used as received from commercial suppliers in sure-seal bottles: diethylcyanamide, lithium dimethylamide, n-BuLi (1.6 M in hexanes), lithium

bis(trimethylsilyl)amide, 1,1,3,3-tetramethyl-1,3-diphenyldisilazane, Lithium bis(dimethylphenylsilyl)amide was prepared according to literature procedure25, CuCl,

AgBr, and AuCl. A Bruker Tensor 27 Instrument with a nitrogen atmosphere was used to obtain FT-IR data to analyze the samples in KBr. Perkin-Elmer 2400 Series 2 CHN-S/O elemental analyzer was utilized to obtain the Elemental Analysis. Electrothermal Mel-

Temp was used to determined melting point and decomposition of samples. The compounds were sealed in glass capillaries under argon in the glove box. Toluene-d8 was used as a solvent for NMR samples. These were prepared under an argon or nitrogen atmosphere by re-dissolving the solid crystals. A Bruker DRX 400 spectrometer was used to obtain NMR data at 400.1 and 100.6 and 79.5 MHz for 1H and 13C and 29Si experiments, respectively.

[Synthesis of [Cu2(μ-NMe2){µ-N(SiMe3)2}]2 (1)

A THF solution of lithium dimethylamide (0.27 g, 5.3 mmol) (5 mL) was added dropwise to a THF solution of lithium bis(trimethylsilyl)amide (0.88 g, 5.2 mmol) (5 mL). A THF solution of CuCl (1.06 g, 10.7 mmol) (5 mL) was added dropwise. A blackish brown solution formed which was allowed to stir for 2 hrs. The solution was concentrated, the liquid was decanted, centrifuged, and allowed to evaporate. Clear, colorless crystals were

1 formed within 24 hrs. Yield 59% (0.99 g) MP (dec.) 160 ºC . H-NMR (400.1MHz, C7D8):

13  = 2.303 (s, 6H, NH2),  = 0.398 (s, 6H, NH2),  = 0.980 (s, 36 H, SiCH3). ). C NMR

-1 (100.6 MHz, C7D8):  = 30.1 (N(CH3)2),  (SiCH3). FT-IR (KBr, cm ) 3919 (w), 3426

(w), 2947 (w), 2771 (w), 2341 (s), 1992(s), 1801 (w), 1750 (m), 1663(w), 1593 (w), 1247

(m), 1131 (s), 1037 (m), 1037 (s), 920 (w), 838 (w), 673 (m), 617 (s), 563 (s) 481 (m).

Synthesis of [Cu2(µ-N=C(Ph)(NMe2){µ-N(SiMe3)2}]2 (2)

A THF solution of lithium 1,1-dimethyl-2-phenylamidinate was prepared according to a slightly modified literature procedure.37 Lithium dimethylamide (0.27, 5.2 mmol) was dissolved in 10 mL THF. Benzonitrile (0.52 g, 5.0 mmol) was dissolved in 8 mL THF and added dropwise to the Lithium dimethylamide solution and allowed to stir for 24 hrs. An orange/brown solution was observed. A THF solution of lithium bis(trimethylsilyl)amide

(0.85 g, 5.1 mmol) (5 mL) was added dropwise. CuCl (1.08 g, 10.9 mmol) was suspended in THF (10 mL) and added dropwise. The solution was black and became green after concentrating. The solution was concentrated to ~3 mL and centrifuged. A black solution was decanted, placed in a -35 ºC freezer and black crystals formed after 24 hrs. Yield 52%

1 (0.97 g) MP (dec.) 166 ºC. H-NMR (400.1 MHz, CDCl3):  = 7.41 (m, 4H,

N=C(N(CH3)2)(C6H5)), 7.28 (m, 6H, N=C(N(CH3)2)(C6H5)), 3.00 (s, 12H,

13 N=C(N(CH3)2)(C6H5)), 0.09, 0.08, 0.07 (s, 36H, N(Si(CH3)3)2). C NMR (100.6 MHz,

CDCl3):  =  (N=C(N(CH3)2)(C6H5)), 129.3 (N=C(N(CH3)2)(C6H5)), 128.4

(N=C(N(CH3)2)(C6H5)), 127.7 (N=C(N(CH3)2)(C6H5)), 127.2 (N=C(N(CH3)2)(C6H5)),

-1 40.7 (N=C(N(CH3)2)(C6H5)), 7.2, 6.8, 6.4 (N(Si(CH3)3)2). FT-IR (KBr, cm ) 3060 (w),

3024 (w), 2942 (m), 2898 (w), 2846 (w), 2813 (w), 2790 (w), 1590 (s), 1573 (m), 1508

(w), 1489 (w), 1474 (w), 1438 (w), 1402 (w), 1350 (m), 1291 (w), 1257 (m), 1244 (m),

1211 (w), 1131 (w), 1066 (m), 1025 (w), 926 (s), 860 (m), 842 (s), 831 (s), 794 (w), 776

(w), 760 (w), 751 (w), 701 (m), 675 (w), 626 (w), 615 (w), 550 (w).

Synthesis of [Cu2{µ-N=C(NMe2)(NEt2)}{µ-N(SiPhMe2)2}]2 (3)

A THF solution of this (0.59 g, 2.0 mmol) (5 mL) was dissolved and placed in a -35 ºC freezer. Lithium dimethylamide (0.10 g, 2.0 mmol) was dissolved in 10 mL of THF.

Lithium diethylcyanamide (0.20 g, 2.0 mmol) was added dropwise to the lithium dimethylamide solution. The lithium bis(dimethylphenylsilyl)amide solution was removed from the freezer and added dropwise. CuCl (0.40 g, 4.0 mmol) was added and the solution stirred for 1 hr. The greenish gray solution was concentrated to 5 mL and centrifuged. The solvent was allowed to evaporate and the resulting black oil was rinsed in 10 mL cold hexane. The liquid was decanted and the solid was redissolved in a mixture of toluene and hexane, centrifuged again, and the solvent was evaporated. After dissolving in toluene again and evaporating, crystallization was finally achieved. Yield 10% (0.118 g), Anal.

Calcd. for C26H68Cu4N8Si4: C 36.34, H 7.98, N 13.04. Found: C 36.30, H 7.75, N 13.84.

1 MP (dec.) 70 ºC. H-NMR (400.1 MHz, C7D8):  = 3.25 (q, JH-H = 7.0 Hz, 4H,

N=C(N(CH2CH3)2)(N(CH3)2)), 2.82 (s, 4H N=C(N(CH2CH3)2)(N(CH3)2)), 2.80 (s, 2H

N=C(N(CH2CH3)2)(N(CH3)2), 1.02 (m, 6H N=C(N(CH2CH3)2)(N(CH3)2), 0.53 (s, 9H

13 N(Si(CH3)3)2), 0.47 (s, 9H N(Si(CH3)3)2). C NMR (100.6 MHz, C7D8):

 =  (N=C(N(CH2CH3)2)(N(CH3)2), 45.1 (N=C(N(CH2CH3)2)(N(CH3)2), 40.8

(N=C(N(CH2CH3)2)(N(CH3)2), 13.4 (N=C(N(CH2CH3)2)(N(CH3)2), 7.2 (N(Si(CH3)3)2).

FT-IR (KBr, cm-1), 3131(s), 3066 (m), 3044 (m), 3020 (w), 2963 (w), 2868 (m), 1572 (s),

1476 (s), 1440 (s), 1425 (s), 1396 (s), 1383 (s), 1363 (s), 1340 (m), 1296 (m), 1249 (s),

1194(s), 1157 (w), 1109 (m), 1066 (m), 1037 (w), 978 (w), 912 (w), 834 (m), 803 (w), 770

(m), 735 (w), 720 (w), 700 (m), 676 (m), 563 (m) 509 (w).

Synthesis of [Ag{μ-N(SiPhMe2)2}]4] (4) and [Au{μ-N(SiPhMe2)2}]4] (5)

Lithium bis(dimethylphenylsilyl)amide (0.40 g, 1.4 mmol) was dissolved in 10 mL of THF.

This solution was placed in the freezer at -35 ºC for 15 minutes. MX (where MX = AgBr

(0.26 g, 1.4 mmol), AuCl (0.32 g, 1.4 mmol) was then added (AgBr was crushed into a fine powder before adding) to LiN(SiPhMe2)2 and allowed to stir for about 90 minutes. The solution was then centrifuged and placed in the freezer overnight. The following day the solution was concentrated and evaporation of the solvent yielded colorless crystals.

[Ag{μ-N(SiPhMe2)2}]4] (4)

Yield 14% (0.29 g). Elemental analysis for C64H88Ag4N4Si8: Calculated (%) 48.9 C, 5.65

H, N 3.57 Found (%) 47.99 C, 5.12 H, 4.17 N. MP (dec.) 124-127 ºC. 1H-NMR

(400.1MHz, C7D8):  = 7.89 (m, 16H, SiC6H5)  = 7.31-7.44 (m, 24H, SiC6H5) 0.69 (s,

13 48H SiCH3). C NMR (100.6 MHz, C7D8):  =  (ipso-SiC6H5),  (ortho-

29 SiC6H5)  (meta-SiC6H5)  (para-SiC6H5),  (SiCH3) Si NMR (MHz

-1 79.5, C7D8):  = -1.99. FT-IR (KBr, cm ) 3069 (m), 3002 (w), 2951(m), 2898 (w), 1591

(w), 1487 (w), 1429 (m), 1302 (w), 1249 (m), 1192 (m), 1113 (s), 1002 (w), 924 (s), 824

(s), 739 (m), 699 (s), 634 (m), 504 (m), 457 (m)

[{Au[(μ-N(SiPhMe2)2]}4] (5).

Yield 10% (0.28 g). MP (dec.) 160 ºC Anal. Calcd. for C64H88Au4N4Si8: Calculated (%) C

39.91, H 4.61, N 2.91 Found (%) 40.04 C, 3.89 H, 3.85 N. MP (dec.) 90-93 ºC. 1H-NMR

(400.1 MHz, C7D8):  = 8.03 (m, 16H, SiC6H5)  = 7.29-7.41 (m, 24H, SiC6H5) 0.77 (s,

13 48H SiCH3). C NMR (100.6MHz, C7D8):  =  (ipso-SiC6H5),  (ortho-

29 SiC6H5)  (meta-SiC6H5)  (para-SiC6H5),  (SiCH3) Si NMR (MHz

-1 79.5, C7D8):  = 2.99. FT-IR (KBr, cm ) 3067 (w), 2955 (w), 2899 (w), 1561 (w), 1487

(w), 1427 (m), 1405 (w), 1248 (m), 1113 (s), 930 (w), 882 (m), 819 (s), 771 (m), 732 (s),

698 (m), 646 (w), 554 (w), 478 (w),463 (w).

X-ray Crystal Structural Information:

X-ray crystallography was utilized in order to collect data regarding the structural composition of these complexes. The crystals were placed in a pool of Fluorolube™ and studied under a microscope in order to find ideal crystal to place on a thin glass fiber. The crystal was then immediately placed under a liquid N2 stream on a Bruker AXS diffractometer using graphite monochromatized Mo K radiation (=0.7107 Å). A least- squares calculation was utilized in order to optimize lattice parameters from carefully centered reflections. Lattice determination, structure refinement, scaling, and data reduction were accomplished via APEX2 software.

Each structure was solved using direct methods. This procedure yielded the heavy atoms, along with a number of the C, Si, and N atoms. Subsequent Fourier synthesis yielded the remaining atom positions. The hydrogen atoms were fixed in positions of ideal geometry and refined within the XSHELL software. These idealized hydrogen atoms had their isotropic temperature factors fixed at 1.2 or 1.5 times the equivalent isotropic U of the C atoms to which they were bonded. The final refinement of each compound included anisotropic thermal parameters on all non-hydrogen atoms. Additional information concerning the data collection and final structural solutions of compounds 1 - 5 can be found at the end of the present chapter. Any variations from standard structural solution associated with the representative compounds, are discussed below. Figures 3 - 7 give a

visual depiction of the planar tetranuclear clusters. Tables 1- 4 also provide further detail including data collection parameters and selected inter-atomic distances.

Results and Discussion:

Synthesis of [Cu2(μ-NMe2){µ-N(SiMe3)2}]2 (1)

The synthesis of 1 is shown in Scheme 5. Lithium dimethylamide and lithium bis(trimethylsilyl)amide were sequentially dissolved in 10 mL of THF. Two equivalents of CuCl were then added to this solution. The solution turned dark brown and was stirred for two hours. The reaction was then concentrated, centrifuged, and a yellow solution was allowed to evaporate and yielded suitable for x-ray diffraction colorless crystals isolated in

59% yield within 24 hours.

Scheme 5. Synthesis of 1.

Synthesis of [Cu2{µ-N=C(Ph)(NMe2}{µ-N(SiMe3)2}]2 (2)

The stepwise synthesis of 2 is shown in Schemes 6 and 7. Lithium 1,1-dimethyl-2- phenylamidinate was prepared in THF according to a slightly modified literature

37 procedure. Lithium dimethylamide was dissolved in 10 mL of THF. To this solution, one

equivalent benzonitrile was added dropwise. This solution was then stirred overnight. One equivalent of lithium bis(trimethylsilyl)amide and two equivalents of CuCl were each suspended separately in 10 mL of THF and then each added dropwise at room temperature to the benzamindinate solution. The combined solution was stirred for two hours and then concentrated to 2 mL, centrifuged and placed in the freezer at -35 ºC. Colorless crystals of

2 were isolated in 10% yield.

Scheme 6: Synthesis of lithium 1,1-dimethyl-2-phenylamidinate.

Scheme 7: Synthesis of Compound 2

Synthesis of [Cu2{µ-N=C(NMe2)(NEt2)}{µ-N(SiPhMe2)2}]2 (3)

The synthesis of 3 is depicted in Schemes 3 and 8. Lithium bis(dimethylphenylsilyl)amide was prepared according to literature procedure.25 This was dissolved in 5 mL of THF. This solution was placed in the freezer at -35 ºC for 15 minutes. Lithium dimethylamide was then dissolved in 10 mL of THF and lithium diethylcyanamide was added dropwise at room

temperature. The solution was stirred and also placed in the freezer for 15 minutes. Both lithium solutions were then removed from the freezer and combined. CuCl was then added dropwise to the lithium solution and stirred for approximately 60 minutes. This solution was then concentrated and placed in the freezer. The solution was later centrifuged, rinsed with cold hexane, redissolved in a mixture of toluene and hexane, centrifuged again, and allowed to evaporate. After dissolving in toluene again and evaporating, crystallization was finally achieved and colorless crystals were isolated in 10% yield.

Scheme 8: Synthesis of 3.

Scheme 9: Synthesis of 4.

Scheme 10: Synthesis of 5.

Synthesis of [Ag{μ-N(SiPhMe2)2}]4] (4) and [Au{μ-N(SiPhMe2)2}]4] (5)

The syntheses of compounds 4 and 5 are depicted in Schemes 9 and 10, respectively. Light was excluded from these reactions due to the photosensitivity of the complexes. Lithium bis(dimethylphenylsilyl)amide was prepared according to literature procedure.25 Lithium

bis(dimethylphenylsilyl)amide was dissolved in 10 mL of THF. This solution was placed in the freezer at -35 ºC for 15 minutes. MX (where MX = AgBr, AuCl) was then added

(AgBr was crushed into a fine powder before adding) to LiN(SiPhMe2)2 and allowed to stir for about 90 minutes. The solution was then centrifuged and placed in the freezer overnight.

The following day the solution was concentrated and the solvent was allowed to evaporate to yield colorless crystals. The yields for the silver and gold complexes were recorded at

14% and 10% respectively.

Structural Descriptions:

A list of selected bond lengths and angles for 1 – 5 are reported in Tables 1-6.

[Cu2(μ-NMe2){µ-N(SiMe3)2}]2 (1)

A thermal ellipsoid plot of 1 is shown in Figure 3. The structure of 1 has bond lengths and angles typical of copper amido complexes 19,22,31 with an average Cu – Cu interatomic distance of 2.683 Å. The tetranuclear structure appears to be planar and overall very symmetrical in nature. The angles between the Cu atoms are also nearly 90º (88.11º and

91.89º) thus forming almost a perfect square. This is also the least bulky complex of the series although it is heteroligated. It is observed to have the smallest metal interatomic distances between metal atoms. (Table 6)

[Cu2(µ-N=C(Ph)(NMe2){µ-N(SiMe3)2}]2 (2)

The structure of 2 is depicted in Figure 4. The structure overall is also very symmetrical and additionally demonstrates nearly a square configuration between Cu-N-Cu angles

(91.12º). When compared to the metal interatomic distance of [Cu{μ-N(SiPhMe2)2}]4 at

2.687 Å versus the distance of 2.730 observed for this complex, it could be surmised that

the benzamidinate ligands introduce a greater steric repulsion and thus induce a larger distance between copper atoms. The copper and nitrogen bonds do not appear to be entirely planar as a “butterfly” effect can be observed within the structure due to the slightly outward position of the N atoms.

[Cu2{µ-N=C(NMe2)(NEt2)}{µ-N(SiPhMe2)2}]2 (3)

A thermal ellipsoid plot of 3 is shown in Figure 5. In general, the copper atoms are coplanar, but the overall structure is not very symmetrical. The interatomic distances between copper atoms vary from 2.832 to 2.625 Å. Thus, there is more of a rhombus configuration than square in this case. The average metal interatomic distance is 2.729 Å which is larger than the distance of 2.687 Å reported for [Cu{μ-N(SiPhMe2)2}]4. Thus, it appears that the guanidinate ligands introduce greater repulsions in the overall structure and thus result in the slightly larger separation observed for the Cu-Cu distances.

[Ag{μ-N(SiPhMe2)2}]4 (4)

The silver complex 4 thermal ellipsoid plot is shown in Figure 6 and overall is a very symmetrical and planar complex. The overall angles between Ag atoms are nearly square

(91.00, 88.81º). The interatomic distances between silver atoms averages to be 3.014 Å compared to [{Ag[(μ-N(SiMe3)2]}4] with 3.001 Å between silver atoms. This is logical in that one assumes greater steric repulsions due to the extra phenyl groups on each ligand which would result in a greater distance between the silver atoms.

[Au{μ-N(SiPhMe2)2}]4 (5)

The thermal ellipsoid plot for 5 is shown in Figure 7 and overall is a very symmetrical and planar complex. The short interatomic distance between Au-Au bonds of 3.007 Å is due to

the weak Au-Au interactions. Some interesting observations were found when comparing metal-metal bond distances with the previously reported [Ag{μ-N(SiMe3)2}]4, and [Au{μ-

20,21 N(SiMe3)2}]4. Due to the bulky nature of this ligand, the predicted value of the metal- metal bond distances would theoretically be greater for [Au{μ-N(SiPhMe2)2}]4. However, they are in fact smaller when compared with that of the complex containing only methyl groups (Table 6). This implies potentially greater aurophilic interaction present in 5.

Conclusions:

Commonalities amongst the five compounds described herein include their nuclearity; each of the four metal ions reside in a plane with each ligand bridging between the two metal ions. Overall, the complexes were similar to previously reported metal amido compounds albeit the gold interatomic distances are somewhat short and can possibly be linked to aurophilic interactions.

Table 1. Data Collection Parameters for 1 – 338 Compound 1 2 3

chemical formula C16H48Cu4N4Si4 C30H58Cu4N6Si4 C46H76Cu4N8Si4 formula weight 663.1 869.34 1107.66 temp (K) 220 219.59 200.01

space group triclinic, Pī triclinic, Pī monoclinic, P21/c a (Å) 8.783 9.8146(15) 13.0400(14) b (Å) 9.541(10) 10.3914(16) 20.514(2) c (Å) 10.681(10) 12.2629(18) 11.3488(12) a (deg) 90.24(2) 99.455(4) b (deg) 103.311(18) 107.540(3) 113.839(2) g (deg) 113.34(2) 115.276(3) V (Å3) 795.2(13) 1014.2(3) 2776.9(5) Z 1 1 2 Dcalcd(Mg/m3) 1.385 1.423 1.325 m,(Mo, Ka) (mm-1) 2.798 2.214 1.634 R1a (%) (all data) 0.0654 0.0557, 0.0774 wR2b (%) (all data) 0.0986 0.1462 0.1135

Table 2. Data Collection Parameters for 4 – 5

Compound 4 5

chemical formula C64H88Ag4N4Si8 C64H88Au4N4Si8 formula weight 1569.58 1925.96 temp (K) 189(2) 200.02 space group triclinic, Pī triclinic, Pī a (Å) 10.363(6) 10.3708(7) b (Å) 13.542(8) 13.4273(10) c (Å) 27.139(14) 27.0381(19) a (deg) 78.168(13) 78.0753(18) b (deg) 79.155(14) 79.1239(18) g (deg) 78.798(19) 78.7465(17) V (Å3) 3613(3) 3569.6(4) Z 2 2 Dcalcd(Mg/m3) 1.443 1.792 m,(Mo, Ka) (mm-1) 2.038 8.368 R1a (%) (all data) 5.53 (10.54) 0.1325 wR2b (%) (all data) 14.27 (18.06) 0.136

Table 3: Selected inter-atomic distances (Å) and angles (º) for 1-2

Complex 1 Cu(1)-N(1) 1.905(4) N(2)-C(7) 1.483(6) Cu(1)-N(2) 1.884(4) N(2)-C(8) 1.484(6) Cu(2)-N(1) 1.910(4) Si(1)-C(1) 1.847(6) Cu(2)-N(2) 1.887(4) Si(1)-C(2) 1.851(6) Cu(2)-Si(1) 2.945(3) Si(1)-C(3) 1.842(6) N(1)-Si(1) 1.742(4) Si(2)-C(4) 1.856(6) N(1)-Si(2) 1.752(4) Si(2)-C(5) 1.845(6) Si(2)-C(6) 1.859(6)

Cu(2)-Cu(1)-Cu(21) 88.11 N(11)-Cu(2)-Si(11) 54.53 N(1)-Cu(1)-Cu(21) 45.26 Cu(1)-N(1)-Cu(21) 89.63 N(1)-Cu(1)-Cu(2) 133.38 Cu(1)-N(2)-Cu(2) 90.43 N(2)-Cu(1)-Cu(2) 44.82 Si(2)-N(1)-Cu(21) 107.91 Cu(1)-Cu(2)-Si(11) 138.23 N(1)-Si(2)-C(3) 111.8 Cu(11)-Cu(2)-Si(11) 64.07 C(3)-Si(1)-Cu(21) 91.5

Complex 2 Cu(1)-N(1) 1.914 Si(1)-C(3) 1.877(6) Cu(1)-N(2) 1.854 Si(2)-C(4) 1.878(7) Cu(2)-N(11) 1.915 Si(2)-C(5) 1.863(7) Cu(2)-N(2) 1.853 Si(2)-C(6) 1.858(6) N(1)-Si(1) 1.742 C(7)-C(10) 1.469(7) N(1)-Si(2) 1.75 C(10)-C(11) 1.411(8) N(2)-C(7) 1.287 C(10)-C(15) 1.408(8) N(3)-C(7) 1.388 C(11)-C(12) 1.368(11) N(3)-C(8) 1.463 C(12)-C(13) 1.404(13) N(3)-C(9) 1.465 C(13)-C(14) 1.395(12) Si(1)-C(2) 1.870(6)

N(1)-Cu(1)-Cu(21) 44.45(12) Si(1)-N(1)-Cu(21) 109.6(2) N(2)-Cu(1)-Cu(21) 133.75(13) Si(1)-N(1)-Si(2) 124.8(2) N(1)-Cu(1)-N(21) 176.54(18) Si(2)-N(1)-Cu(1) 107.3(2) N(11)-Cu(2)-Cu(11) 44.43(12) Si(2)-N(1)-Cu(21) 110.3(2) N(2)-Cu(2)-Cu(11) 131.56(13) Cu(2)-N(2)-Cu(1) 94.66(18) N(2)-Cu(1)-N(1) 175.79(18) C(7)-N(2)-Cu(1) 128.6(4) Cu(1)-N(1)-Cu(21) 91.12(17) C(7)-N(2)-Cu(2) 136.7(4) Si(1)-N(1)-Cu(1) 108.4(2)

Table 4: Selected inter-atomic distances (Å) and angles (º) for 3

Complex 3 Cu(1)-N(1) 1.851(3) N(1)-C(1) 1.284 Cu(1)-N(4) 1.913(3) N(2)-C(1) 1.390(6) Cu(2)-N(1) 1.853(3) N(2)-C(4) 1.468(7) Cu(2)-N(41) 1.920(3) N(3)-C(6) 1.451(6) N(4)-Si(1) 1.744(3) Si(1)-C(14) 1.878(5) N(4)-Si(2) 1.750(3) Si(1)-C(15) 1.860(4)

N(1)-Cu(1)-Cu(21) 129.01(10) C(1)-N(1)-Cu(1) 132.1(3) N(1)-Cu(1)-N(4) 171.79(14) C(1)-N(1)-Cu(2) 128.1(3) N(4)-Cu(1)-Cu(21) 46.85(9) Cu(1)-N(1)-Cu(21) 86.52(12) N(1)-Cu(2)-Cu(11) 131.20(9) Si(1)-N(4)-Cu(1) 116.23(17) N(1)-Cu(2)-N(41) 171.77(14) Si(1)-N(4)-Cu(21) 112.92(16) N(41)-Cu(2)-Cu(11) 46.62(9) Si(2)-N(4)-Cu(1) 107.13(15) Cu(1)-N(1)-Cu(2) 99.78(15) Si(2)-N(4)-Cu(1) 107.44 (16)

Table 5. Selected inter-atomic distances (Å) and angles (º) for 4 - 5

Compound 4 Ag(1)-N(2) 2.156(6) Ag(2)-N(2) 2.174(7) Ag(1)-N(1) 2.157(6) Ag(3)-N(3) 2.169(6) Ag(2)-N(3) 2.150(7) Ag(4)-N(1) 2.136(7) Si(1)-N(1) 1.754(7) Ag(4)-N(4) 2.160(6)

N(2)-Ag(1)-N(1) 179.6(3) N(1)-Ag(1)-Ag(4) 45.17(18) N(2)-Ag(1)-Ag(4) 135.16(18) N(2)-Ag(1)-Ag(2) 46.14(17) N(1)-Ag(1)-Ag(2) 132.25(18) Ag(4)-Ag(1)-Ag(2) 91.46(5) N(3)-Ag(2)-N(2) 177.3(2) N(3)-Ag(2)-Ag(1) 131.99(17) N(2)-Ag(2)-Ag(1) 45.65(17) N(2)-Ag(2)-Ag(3) 131.57(17) N(3)-Ag(2)-Ag(3) 45.78(17) N(3)-Ag(3)-N(4) 179.5(3) Ag(1)-Ag(2)-Ag(3) 88.36(5) N(3)-Ag(3)-Ag(4) 134.25(18)

Compound 5 Au(1)-N(2) 2.103(11) Au(4)-N(1) 2.078(11) Au(1)-N(4) 2.096(11) Au(4)-N(3) 2.092(11)

N(1)-Si(1) 1.783(11) Au(2)-N(1) 2.094(10) N(1)-Si(2) 1.777(11) Au(2)-N(2) 2.090(10) N(2)-Si(3) 1.766(11)

N(3)-Si(4) 1.794(11) Au(3)-N(3) 2.102(11) Si(1)-C(1) 1.834(15) Au(3)-N(4) 2.101(11) Si(2)-C(2) 1.855(14)

Au(2)-Au(1)-Au(3) 88.81(2) N(1)-Au(2)-Au(1) 132.3(3) N(2)-Au(1)-Au(2) 44.0(3) N(1)-Au(2)-Au(4) 43.6(3) N(2)-Au(1)-Au(3) 130.7(3) N(2)-Au(2)-Au(1) 44.3(3) N(4)-Au(1)-Au(2) 130.8(3) N(2)-Au(2)-Au(4) 133.3(3) N(4)-Au(1)-Au(3) 44.1(3) N(2)-Au(2)-N(1) 176.6(4) N(4)-Au(1)-N(2) 174.7(4) Au(4)-Au(3)-Au(1) 91.08(3) Au(1)-Au(2)-Au(4) 91.00(3) N(3)-Au(3)-Au(1) 132.9(3)

Table 6: Metal – Metal Interatomic Distances for 1-5 compared with literature values

Compound M-M (Å) Reference

[Cu2(μ-NMe2){µ-N(SiMe3)2}]2 2.683 (1) 19 [Cu2{µ-N(SiMe3)4}]2 2.685

[Cu2{µ-N=C(Ph)(NMe2)}{µ-N(SiMe3)2}]2 2.730 (2)

[Cu2{µ-N=C(NMe2)(NEt2)}{µ-N(SiPhMe2)2}]2 2.729 (3) 26 [Cu{μ-N(SiPhMe2)2]}4 2.687

20 [Ag{μ-N(SiMe3)2}]4 3.001

[Ag{μ-N(SiPhMe2)2]}4 3.014 (4)

21 [Au{μ-N(SiMe3)2}]4 3.023

[Au{μ-N(SiPhMe2)2}]4 3.007 (5)

Figure 2. Thermal ellipsoid plot of 1. Ellipsoids are drawn at 30 % level. H atoms have been omitted for clarity.

Figure 3. Thermal ellipsoid plot of 2. Ellipsoids are drawn at 30 % level. H atoms have been omitted for clarity.

Figure 4. Thermal ellipsoid plot of 3. Ellipsoids are drawn at 30 % level. H atoms have been omitted for clarity.

Figure 5. Thermal ellipsoid plot of 4. Ellipsoids are drawn at 30 % level. H atoms have been omitted for clarity.

Figure 6. Thermal ellipsoid plot of 5. Ellipsoids are drawn at 30% level. H atoms have been omitted for clarity.

CHAPTER III

NANOMATERIALS SYNTHESIS AND CHARACTERIZATION

Introduction:

In this experiment, a capping agent that had previously not been investigated was investigated. N,N-Dimethylhexadecylamine (HDA) was used as both a solvent and capping agent. The high boiling point of this compound at (323.6 ºC) allows for the synthesis to take place at elevated temperature. While more moderate temperatures (100-200 ºC) typically lead to nanospheres, the reaction described herein was carried out at 300 ºC. This is advantageous to keeping the NPs in liquid form in order for optimal nucleation and growth to occur. 14

Experimental:

Nanocrystal Synthesis

The synthesis of Cu2O nanocrystals was carried out under inert conditions via glovebox and Schlenk line techniques. N,N-Dimethylhexadecylamine (7.8 g, 29 mmol) was added to a three-neck 100 mL flask. The preparation of the precursor additionally was accomplished under an atmosphere of nitrogen. The injection of a 0.225 M (0.105 g) solution of CuCl in

N,N-dimethylhexadecylamine at 300 ºC was then carried out. The reaction was allowed to stir for approximately 60 seconds before the solution was removed from heat and allowed to cool to room temperature. The solution was then exposed to air, resulting in the red-

purple solution eventually turning blue-green. The particles were then washed in 10 mL of methanol and redispersed in toluene.

Nanocrystal Characterization:

A Varian Cary 50 Bio UV-visible Spectrophotometer was utilized from 400 – 800 nm to perform UV-Vis spectroscopy of the toluene solution. The particles were then placed on nickel TEM grids and viewed under Tecnai G2 F20 Transition Electron Microscope (200 kV).

Results and Discussion:

Although the nanocrystals were exposed to air, they were still able to maintain their colloidal nature. Typically, when exposed to air, copper crystals tend to react with oxygen to form CuO which leads to agglomeration of the particles on account of surface oxidation.39 TEM imaging (Figures 9-12) revealed that the particles are not uniform in size and range from 2.75 nm to 40.85 nm. Haruta previously reported Cu2O nanocrystals of 4 nm40 which appears to be about the average size of the particles. In addition, the observation of various shading among the nanocrystals reveals that they are in fact crystalline.. UV-Vis spectroscopy was also in accordance with the absorption spectra of previously reported nanocrystals by Lou et al with a peak at 659 nm.. Our prepared sample had a max of 707 nm. Overall, while the nanocrystals were exposed to air, they still have potential in many applications and the general synthesis may be modified to accommodate more elaborate precursor materials such as those described in Chapter II.

Figure 7. UV-VIS spectra of Cu2O Nanocrystals

Figure 8. TEM image of Cu2O Nanocrystals

Figure 9. TEM image of Cu2O Nanocrystals

Figure 10. TEM image of Cu2O Nanocrystals

Figure 11. TEM Image of Cu2O Nanocrystals

Figure 12. TEM Image of Cu2O Nanocrystals

CHAPTER IV

CONCLUSIONS

Overall, this project yielded the successful synthesis, isolation, and characterization of five novel copper, silver, and gold clusters. Characterization methods included NMR

(various nuclei), IR spectroscopy, melting point decomposition, single crystal X-ray diffraction, and elemental analysis. Commonalities amongst these low-coordinate metal amides include their oxidation number of +1, coordination number of 2, bridging ligands, coplanar metal centers with angles between nitrogen atoms at nearly 90º angles. These complexes reveal additional information about closed-shell interactions between the coinage-metals which have fascinated people for hundreds of years. Compound 5 is a good example of the aurophilicity of gold which has been a topic of interest within inorganic chemistry for several decades.39,42 These complexes allow for further insight into the closed-shell interactions of which have been an additional long term research topic within the field.

Despite the highly sensitive nature of these compounds, there are many applications and much opportunity to build upon the information garnered from this project. The future complexes to be explored may include Ag and Au analogs of 1-3, as well as replacing

LiN(SiPhMe2)2 for LiN(SiMe3)2 in the overall synthesis of 1 and 2. The possibility of these clusters for applications in nanocrystals requires further research as the temperature and conditions of the nanocrystal reaction remains under investigation.

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