Structural and ab initio studies of AgAg bonding in the silver(I) dimer bis-μ-(5,7-dimethyl[1,2,4]triazolo[1,5- a]pyrimidine)dinitrato disilver(I)

Abstract

This work is an attempt to address the issue of metal-metal bonding in d 10 systems. The compound [Ag(dmtp)(NO 3)] 2, where dmtp represents the ligand 5,7-dimethyl[1,2,4]triazolo[1,5- a]pyrimidine, has been prepared, characterized by thermal analysis and IR spectroscopy and its structure has been solved by X-ray diffraction. The compound is triclinic, space group P 1 ̄ , a = 5.1295(4), b = 9.6009(7), c = 10.332(2) A ̊ , α = 103.73(1), β = 99.14(1), γ = 97.67(1)°, Z = 2, D cal = 2.200 g cm −3, R = 0.029 for 4144 observed reflections. The compound exhibits a [Ag 2(dmtp) 2] 2+ core structure with two silver atoms bridged by the dmtp ligands via N3 and N4 to give eight-membered Ag 2N 4C 2 rings. The nitrato groups are coordinated in a semibridging and semichelating way (distances AgO, 2.816(2) Å for non-bridging and 2.653(2) and 2.749(2) Å for bridging oxygens). The AgAg separation is 3.058(1) Å, only 0.17 Å greater than in metallic silver. In order to make checking of the possible AgAg bonding, a theoretical analysis has been performed, based on the properties of the charge density distribution derived from ab initio MO calculations using STO-3G∗ and 3-21G(∗) wavefunctions, a significant direction interaction between the two metal centres having been found. Similar conclusions have been obtained for the model compound [Ag(NHCHNH)] 2 after performing a geometry optimization and using improved LANL2DZ wavefunctions that take into account relativistic effect.