Mechanism of formation of [Ag2L2I2] and crystal structure of the intermediate [Ag3L2I3] cluster (L = 1,8-diisocyano-p-menthane)
Abstract
The complexes [AgnL2In](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.