MECHANISM OF FORMATION OF [AG2L2I2] AND CRYSTAL-STRUCTURE OF THE INTERMEDIATE [AG3L2I3] CLUSTER (L = 1,8-DIISOCYANO-P-MENTHANE)

The complexes [AgnL2In] (n = 2-4, L = 1,8-diisocyano-p-menthane) have been prepared from the direct reaction of AgI with L in the appropriate stoichiometric amount and have been identified either by chemical analysis and fast atom bombardment mass spectroscopy (n = 2 or 4), or by X-ray crystallography (n = 2 or 3). Addition of excess of L to benzene solutions of AgI, [Ag4L2I4] or [Ag3L2I3] always led to [Ag2L2I2], indicating that the synthesis of the Ag, complexes from AgI 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)-degrees] with the following r(Ag ... Ag) values: 3.633(4), 3.760(4) and a relatively short one of 2.805(4) angstrom. The triangular structure is bicapped by two iodine atoms [r(Ag-1) ranging from 2.789(3) to 3.085(5) angstrom], while the third iodine atom bridges the two least separated Ag atoms. The Raman-active v(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 angstrom-1). These non-bonding Ag ... Ag interactions correspond approximately to an Ag-Ag bond order of almost-equal-to 0.5.