An in-depth examination of the properties and behaviour of Au(III)-based [AuX2(CN)2]- (X = Cl, Br, I) as a coordination polymer building block

Date created: 
Daniel Leznoff
Science: Chemistry
Coordination polymer
Reductive elimination
Weak interaction

This thesis primarily focuses on the synthesis and characterization of [AuX2(CN)2]- (X = Cl, Br, I), a square planar Au(III)-based compound, and its use as a coordination polymer building block. K+, nBu4N+ and PPN+ salts of [AuX2(CN)2]- and the Au(I/III)-based double salts K3[Au(CN)2]2[AuBr2(CN)2]-H2O and K5[Au(CN)2]4[AuI2(CN)2]-2H2O were prepared and structurally characterized. All compounds exhibited many structure-defining weak interactions such as X-X, Au-X (X = Br, I) and Au(I)-Au(I) interactions, as well as a rare Au(I)-Au(III) interaction with an intermolecular distance of 3.58 A; no Cl-Cl interactions were observed. [AuX2(CN)2]- was introduced to solutions containing a variety of divalent metals (Mn, Fe, Co, Ni, Cu, Zn, Pb) and ancillary N-donating chelating ligands such as 1,10-phenanthroline or bridging ligands such as 4,4'-bipyridine. In most cases, an ionic material resulted, containing a metal cation coordinatively saturated by ligand and an unbound [AuX2(CN)2]- (X = Cl, Br) anion. In some cases, [AuX2(CN)2]- did bind, but in a pendant, non bridging fashion. With ethylenediamine and 4,4'-bipyridine ligands, and Ni(II) and Co(II) or Zn(II), respectively, an [AuBr2(CN)2]--bridged coordination polymer resulted; no [AuCl2(CN)2]--bridged materials were observed with added ancillary ligands. In the absence of ancillary ligand, several [AuX2(CN)2]--bridged (X = Cl, Br) formed; all reactions involving [AuI2(CN)2]- resulted in decomposition of the [AuI2(CN)2]- molecule. Exposing [AuX2(CN)2]- to temperatures above 80 C or UV light resulted in the reductive elimination of halogen, yielding [Au(CN)2]-. Kinetics (thermal and photochemical) studies revealed pseudo first-order rate kinetics with. Heating some [AuBr2(CN)2]--containing coordination polymers to 125 C converted them to analogous [Au(CN)2]--containing materials. The ligand-free Cu[AuX2(CN)2]2 materials exhibited a vapochromic response when exposed to H2O, DMF, DMSO, pyridine, 1,4-dioxane and ethyleneglycol; they also exhibited distinct IR and Raman vCN patterns. Using Raman analysis, these vCN patterns can be effectively used to detect and identify between DMF, DMSO and pyridine. A series of Cu(I) and Ag(I)-based coordination polymer materials containing bridging [AuX2(CN)2]-, [Au(CN)4]- and [Au(CN)2]- were synthesized and characterized. M[Au(CN)4] (M = Cu, Ag) exhibit negative thermal expansion with expansion coefficients between -11e-6 and -24e-6 K-1. M[Au(CN)2] are isomorphous to known AuCN, and exhibit turquoise (Ag) and red (Cu) emission. Incorporating pyridine, THT, PPh3 and Me2S in the Cu(I)/[Au(CN)2]- reaction yielded materials with distinct emissive properties; Cu(SMe2)[Au(CN)2] emits white light. Thus, Cu[Au(CN)2] shows potential as a sensor for P- or S-donor solvents.

Thesis type: 
(Thesis) Ph.D.
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