STRUCTURAL AND AB-INITIO STUDIES OF AG-AG BONDING IN THE SILVER(I) DIMER BIS-MU-(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 P (1) over bar, a = 5.1295(4), b = 9.6009(7), c = 10.332(2) Angstrom, alpha = 103.73(1), beta = 99.14(1), gamma = 97.67(1)degrees, 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 Ag2N4C2 rings. The nitrate groups are coordinated in a semibridging and semichelating way (distances Ag-O, 2.816(2) Angstrom for non-bridging and 2.653(2) and 2.749(2) Angstrom for bridging oxygens). The Ag-Ag separation is 3.058(1) Angstrom, only 0.17 Angstrom 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.