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A Structural and Dynamic Study of Cryptates

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A Structural and Dynamic Study of Cryptates 2r-l"q I A Structural and Dynamlc Study of Cryptates AMIRA ABOU-HAMDAN B.Sc. (American University of Beirut) B.Sc.(Hons.) (University of Adelaide) This thesis is presented for the degree of Doctor of Philosophy Department of Physical and Inorganic Chemistry University of Adelaide July, 1990 Arnira Abou-Hamdan 1 C ontents Summary lv S tatem ent vll Acknow ledge ments v1l1 Abbreviations IX Chapter 1. General Introduction 1 Chapter 2. Structural Aspects of Cryptates 6 2.t Introduction 6 2.2 Experimental 13 2.2.1 Materials 13 2.2.2 NMR Spectroscopy 13 2.2.3 Crystallography l3 (a) X-ray Crystallography of ÍLl.C2lCslNCS l3 (b) X-ray Crystallography of [K.C2l(NCS)] 20 2.3 Results and Discussion 26 2.3.1 X-ray Crystallography 26 2.3.2 Cryptate Structure in Solution 31 (a) 13C Nun Specrroscopy 31 (b) 7ti NIr,tR Spectroscopy 38 Arnira Abou-Hamdan l1 Chapter 3. Cryprate Stabiliry 42 3.1 Introduction 42 3.2 Stability constant Determination 49 3.2.1 Determination of Cryptate Stability Constants by NMR Spectroscopy 49 3.2.2 Determination of Cryptate Stabiliry Constants by Potentiometric Titration 50 3.3 Results and Discussion 53 Chapter 4 Kinetic and Mechanistic Aspects of the Cryptates of C2ICs, C22CZ and Czll 65 4.1 Introduction 65 4.2 Kinetic Applications of NMR Spectroscopy 67 4.2.1 7Li NtvtR Spectroscopy 6l 4.2.2 23Na NMR Spectroscopy 69 4.2.3 Kinetic Applications 69 4.2.4 Lineshape Analysis 78 4.2.5 Calculation of Activation Parameters 80 4.3 Results and Discussion 82 4.3.t General Mechanistic Aspects of Cryptates 82 4.3.2 Exchange Kinetics of Li+ on [Li.C2lCs]* 84 4.3.3 Exchange Kinetics of Na* on [Na.C211]* and [Na.C2lC5]+ 94 4.3.4 Exchange Kinetics of Li+ on [Li.C22Cz]* 100 4.3.5 General Conclusions t07 Atnira Abou.-Hamdan ul Chapter 5. Experimental 110 5.1 Materials 110 5.2 Synthesis 111 5.2.1 Preparation of C2lC5 111 5.2.2 Preparation of C22Cz rt2 5.3 Stability Constant Measurements 113 5.4 Preparation of NMR Samples lr5 5.5 In stru m entation 115 List of Publications 118 B ibl iography t20 Appendix 1 Lineshape Analysis Data 132 Appendix 2 Supplementary Crystallographic Data t43 Amira Abou-Hamdan lV Summ ary The crystal structures of the cryptate [Li.C2lCs]NCS and the diaza crown ether complex [K.C21]NCS have been determined by X-ray crystallography. The structures are compared with structures of related cryptates and diaza crown complexes to afford an assessment of the effeit of variation of the position and number of donor atoms in cryptands on the structure of alkali metal cryptates. The complexation of Li* by the cryptand C2lC5 has been studied in seven solvents by 7Li nmr spectroscopy and potentiometric titration. The stability constants tog{Ksldm3 mol-1} values at 298.2 K, for [Li.C21C5]* and [Ag.C21C5]. respectively are: in acetonitrile (4.15, 4.29), methanol (3.01 , J.69), dimethylformamide (1.80, 5.23), dimethylacetamide (1.85 , 4.45), and diethylformamide (1.72, 4.95). The Li+ exchange on the LLi.CzlC5l* is in the very slow regime of the 7fi nmr timescale in acetonitrile, propylene carbonate, and acetone, and within the 1Li nmr timescale in methanol, dimethylformamide, dimethylacetamide, and diethylformamide. Thus the respective decomplexation rate constants obtained from subsequent lineshape analysis are k¿ (298.2 K) = 2I.6 * 0.4, lL6 + 2,237 * 4, and 210 * 4 s-l The corresponding activation parameters are L,H. = 36.L + 0.9, 38.4 * 0.9, 49.0 * 2.1, and 27.8 + 1.5 kJ mol-l and Â^S* = -98.4 * 3.1, -76.5 * 3.0, -35.0 + 2.8, and -108 + 5 J K-l mol-l. The variation of the 13C and 7Li chemical shifts of ÍLi.CzlCsl* with solvent is employed in a structural investigation of this cryptate in solution. The equitibrium and kinetic data are discussed in conjunction with data from other related cryptates. Amira Abou-Hamdan V complexation of Na* by the closely related ligands C2l, Czll and C2lC5 has been studied by 23Na nmr spectroscopy and potentiometric titration. The stability constants log{Ks/dm3 mol-1} values at 298.2 K for [Na.c2l]* in the three solvents dimethytformamide, dimethylacetamide and diethyformamide (of similar electron donating strength but different molecular size) are 2.10, 2.88 and 3.lg respectively, The log{Ksldm3 mol-l} values at 298.2 K, for [Na.C2rCs]* and [Na.c211]* respectively are: in dimethytacetamide (2.05, 4.74), and in diethylformamide (2.52, 5.10). The Na* exchange on the [Na.C2lCs]* is in the very fast regime of the 23Na nmr timescale in dimetylacetamide and diethylformamide. The Na* exchange on the [Na.C211]* is within the 23Na nmr timescale in diethylformamide. Thus the decomplexation rate consranr obtained is k¿ (298.2 K) = l8.z + 2.0 s-l and the corresponding activation parameters are L,H* = 67.1 + 1.9 kJ mol-l and Âs* = 4.4 * 5.0 J K-l mol-I. These data are compared with each other and with similar complexes in the light of tigand and solvent molecular characteristics. complexation of Li+ and Ag* by the clam-like cryptand c2zcz has been studied in seven solvents by 1Li nmr spectroscopy and potentiometric titration. The stability constants log{Ksldm3 mol-l} values at 298.2 K, for lLi.c22c2l. and l{g.c22c2l* respectively are: in acetonitrile (7.8, 9.4), acetone (8.9, 13.1), water (<2, 6.0), methanol (4.0, r0.2), dimethylformamide (3.5, 9.4), diethylformamide (3.1, B.z), and pyridine (4.0, 5.0). The Li* exchange on the lLi.C22C2l+ is in rhe very slow regime of the 7Li nmr timescale in acetonitrile, acetone and pyridine, in the very fast regime in water, and within the 7Li nmr timescale in methanol, dimethylformamide and diethylformamide. Thus the respective decomplexation rate constants obtained are k¿ Amira Abou.-Hamdan vl (298.2 K) :971 + 42,240 + 7, and 916 + 28 s-1. The corresponding activation parameters are LH* :31.0 + 0.4,22.5 + r.2 and 26.7 * 0.6 kJ mol-l and Â,S* : -84.0 + 2.6, -I24 + 5 and -98.6 * 2.3 J K-l mol-l. These data aÍe discussed in the context of the effects of cryptand structure and solvent characteristics on cryptate lability and stability. Amira Abou.-Hamd.an vltl Acknowledgements I sincerely wish to thank my supervisor, Dr s.F. Lincoln for his guidance, encouragement, and support throughout the course of this work. I wish to thank my associates for their helpful discussion and suggestions, and my colleagues for their invaluable support .I especially wish to thank Andrea Hounslow for her advice on the operation of the spectrometers, and particularly for her encouragement and friendship. Many sincere thanks go to my relatives and friends for their endless support. I gratefully acknowledge the financial support of a Commonwealth Postgraduate Research Award for the period of my candidature. Finally, I wish to dedicate this thesis to my family whose support, interest, and encouragement throughout my academic years made the achievement of this work possible. Amira Abou-Hamdan 1X Abbreviation s The following abbreviations have been used in this thesis: Czl 4,7 ,13 -trioxa- I , 10-diazacyclopentadecane C22 4,J,13,Ií-tetraoxa-1,I0-diazacyclooctadecane C2lC5 4,7 ,l3 -trioxa- I ,L}-diazabicyclo t8.5.51eicosane C22C2 4;7,13,16-tetraoxa-1,I0-diazabicyclo[8.8.2]eicosane CZI I 4,7 ,13, 1 8-tetraoxa- I ,|}-diazabicy clo t8.5.51eicosane C221 4,7 ,13 ,16,21 -penraox a-I ,I0-diazabi cy clo t8.8.51tricosane c222 4,7,13,16,21,24-hexaoxa-1,r}-diazabicyclotS.S.Sloctacosane MeOH m ethan ol DMF N,N-dimethylformamide DEF N,N-diethylformamide DMA N,N-dimethylacetamide MeCN acetonitrile PC propylene carbonate TEAP tetraethylammonium perchlorate CDCI3 the D represents the deuterium 12¡1;, also in the cases of D2O and (CD3)2CO. d n - n-deuterated- DNI Gutmann donor number n m r nuclear magnetic resonance F.I.D. free induction decay r.f. radio frequency ò chemical shift Hz Hertz p p m parts per million Arnira Abou-Hamdan Chapter 1 General Introduction The study of the complexation of metal ions and other species by multidentate macrocyclic ligands has been rapidly developing since the discovery of crown-ethers (macrocylic polyethers) in 1967 by Pedersen 11 ,2,3), the introduction of cryptands (polyoxadiazabicycloalkane ligands) in 1968 by Lehn [4], and the more recent contribution by Cram in the synthesis of a new class of molecules, the spherands [5,6]. All three scientists have been the recipients of the 1987 Nobel prize in chemistry. This developing field is described by Lehn as "supramolecular chemistry' (and is also called "inclusion chemistry"), where the new supermolecules, of the types described above, or "hosts" bind the substrates or "guestn species by bonding interactions varying from those with significant covalent character to those which are of a secondary bonding character. Pedersen discovered the first crown-ether, dibenzo-18-crown-6 (Figure I .1), in the process of improving a method for olefin polymerization, catalyzed by vanadium complexes. Crown-ethers are cyclic molecules which form complexes with alkali metal ions. r^oì l^oì 00 0 0 0 0 0 \-o'---J \-oJ Figure 1.1 Dibenzo-18-crown-6 and its potassium complex. Atnira Abou.-Hamdan 2 Concurrently, the increasing research on the complexation of alkali cations by naturally occurring macrocyclic antibiotics lead to the determination of the structure and synthesis of valinomycin, and its ability to mediate K+ transport in mitochondria Í71.
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