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

This work is an attempt to address the issue of metal-metal bonding in d 10 systems. The compound [Ag(dmtp)(NO3)]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 PI, a = 5.1295(4), b = 9.6009(7), c = 10.332(2) /~, c~ = 103.73(1), /3 = 99.14(1), 3' = 97.67(1) °, Z = 2, Dca I = 2.200 g cm -3, R = 0.029 for 4144 observed reflections. The compound exhibits a [Ag2 (dmtp)2] 2+ core structure with two silver atoms bridged by the dmtp ligands via N3 and N4 to give eight-membered Ag2N4C2 rings. The nitrato groups are coordinated in a semibridging and semichelating way (distances Ag-O, 2.816(2)/~ for non-bridging and 2.653(2) and 2.749(2) ]~ for bridging oxygens). The A g A g separation is 3.058(1) A, only 0.17 A greater than in metallic silver. In order to make checking of the possible A g A g 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.