Mechanism of formation of [Ag2L2I2] and crystal structure of the intermediate [Ag3L2I3] cluster (L = 1,8-diisocyano-p-menthane)

Abstract

The complexes [Ag_nL₂I_n](n= 2–4, L = 1,8-diisocyano-p-menthane) have been prepared from the direct reaction of Agl with L in the appropriate stoichiometric amount and have been identified either by chemical analysis and fast atom bombaradment mass spectroscopy (n= 2 or 4), or by X-ray crystallography (n= 2 or 3). Addition of excess of L to benzene solutions of Agl, [Ag₄L₂I₄] or [Ag₃L₂I₃] always led to [Ag₂L₂I₂], indicating that the synthesis of the Ag₂ complexes from Agl must proceed via the formation of the Ag₄ and Ag₃ species. The single-crystal X-ray analysis of [Ag₃L₂I₃] reveals the formation of a quasi-isosceles triangular Ag₃ structure [apex angle 44.55(7)°] with the following r(Ag ċ Ag) values: 3.633(4), 3.760(4) and a relatively short one of 2.805(4)Å. The triangular structure is bicapped by two iodine atoms [r(Ag–I) ranging from 2.789(3) to 3.085(5)Å], while the third iodine atom bridges the two least separated Ag atoms. The Raman-active ν(Ag₂) mode associated with this short binding is observed at 122 cm^–1(with a force constant, F extracted from the diatomic approximation, of 0.47 mdyn Å^–1). These non-bonding Ag ⋯ Ag interactions correspond approximately to an Ag–Ag bond order of ≈ 0.5.