Vibrational spectra, force constants and quantum chemical calculations of μ-1,3-azide bridged triphenylphosphine complexes of copper(I) and silver(I)

Abstract

The dimeric title compounds [(C6H5)3P]Cu2(N3)2 and [C6H5)3P]Ag2(N3)2 were synthesized and characterized by FT-Raman and IR spectroscopy. The two phases were not isotypic but possessed approximately the same molecular symmetry which was C2/2m. The assignment of the modes was supported by quantum chemical DFT calculations coupled with TED (Total Energy Distribution) analyses. The calculated (N[sbnd]N) force constants for the bridging –(NNN)– groups were directly comparable (f(N[sbnd]N) = 11.75 (Cu) and 12.19 N cm−1(Ag)) and harmonized well with those of the free azide anion in the binary alkali azides. The (N[sbnd]N) bond orders were obtained based on the calculated force constants (Siebert Bond Order, SBO) and Density-dependent electrostatic and chemical (DDEC6) method yielding SBO = 1.92 (Cu) and 1.96 (Ag) and BO = 2.00 (Cu) and 2.03 (Ag), respectively, indicating the presence of double bonds. The results underlined that the (N[sbnd]N) force constants and bond orders in the bridging azide units were practically unaffected by the nature of the central metal atoms and that they could be regarded as quasi isolated anions similar to those in the binary azide compounds.