Anionic copper(I), silver(I), and gold(I) halide complexes: Structure, symmetry, and luminescence

Scope and method of study. The purpose of this study was to synthesize a determine the accurate geometry of copper(I) silver(I) and gold(I) complexes with single crystal X-ray crystallography, and to evaluate their spectroscopic behavior via room and low temperature luminescence spectroscopy. Evaluation of the electronic structure of the complexes was carried out using Gaussian 98 ab initio computations at the Hartree-Fock SCF level of theory. Correlation between observed emission and the symmetry of the metal halide was made.; Findings and conclusions. Complexes of the type [Ag ₂I₄]2−, [AuI₂]− , [Ag₃I₄]−, [Ag₄I ₈]4−, and [Ag₅I₆] − were isolated and examined by single crystal X-ray diffraction. Gold(I) consistently forms linear AuI₂− complexes such as [K(benzo-15-crown-5)₂](AuI₂). These complexes do not emit in the visible spectrum when excited by ultraviolet radiation. Silver(I), on the other hand, forms a wider range of complexes with iodide, such as [Cs(18-crown-6)](Ag₂I₃)_n a polymeric single ribbon of edge sharing Ag₂I₂ rhombs with every other rhomb bridged by an additional iodide atom in an up, up, down, down sequence, and also flat Ag₂I₄ rhombohedra showing three coordinate silver atoms bridged by two iodide atoms and completing their coordination spheres by ligation to a terminal iodide atom. The silver(I) and gold(I) iodide complexes do not emit upon excitation with ultraviolet radiation, except for [Ba(benzo-15-crown-5)₂]₂ (Ag₄I₈). The silver(I) bromide and copper(I) iodides do emit. Correlation between observed emission and the symmetry of the metal halide complexes shows a general decrease in wavelength of emission with increasing solid state symmetry. All metal halide complexes have significant quadrupole moments and the emitting complexes display a temperature dependence that suggests vibronic coupling as a mechanism that quenches emission. Metal-metal interactions may also be significant in the emission properties.