Silver(I) imidazole perchlorate. An (Ag+)6 cluster and its radiolytically produced one-electron adduct studied by X-ray diffraction and electron spin resonance spectroscopy

Abstract

The crystal structure of silver(I) imidazole perchlorate reveals the presence of a planar (Ag⁺)₆, cluster, in which three radiating pairs of Ag⁺ ions 3.051(1)Å apart are disposed on the corners of an equiliateral triangle, the inner Ag⁺ ions being 3.493(1)Å apart. Each silver ion carries two linearly co-ordinated imidazole ligands, the whole unit has 32(D₃) symmetry. Exposure to ⁶⁰Co γ-rays at 77 K results in electron addition to a group of three equivalent silver atoms. The ¹⁰⁹Ag, ¹⁰⁷Ag, and ¹⁴N hyperfine coupling constants show that the total 5s character of the unpaired electron is only ca. 0.55, and delocalisation onto six equivalent nitrogen ligands accounts for ca. 0.25. Low g values suggest that the remaining spin density is in 5p orbitals on silver. There is no indication of delocalisation onto the remaining three Ag⁺ ions in the cluster. Possible reasons for this selectivity are discussed. The electron-loss centre appears to be a normal Ag²⁺ complex. We suggest that marked distortion results in the hole being trapped on one silver rather than being delocalised.