The effect of N-ligands on the geometry, bonding, and electronic absorption properties of ruthenium carbonyl chains

Abstract

The stability and structural properties of linear chain compounds [Ru(L)(CO)_1–2]_n (L = substituted or unsubstituted 2,2′-biimidazole, 2,2′-bipyridine, 1,10-phenantroline, or 2,2′:6′,2″-terpyridine) were investigated by computational DFT methods. The favored torsional orientation of the neighboring units in the chain was studied using dinuclear (n = 2) models. Models up to 8 [Ru(L)(CO)_1–2] units were used to analyze Ru–Ru interactions by Mayer bond order and charge density analysis. Compared to the related polymeric compound [Ru(CO)₄]_n, the presence of chelating nitrogen ligands led to slightly weaker Ru–Ru bonds. Electronic structures and corresponding excitations were investigated by TD-DFT methods. The studied nitrogen ligands, especially biimidazole compared to polypyridines, were found to produce differences in the absorption characteristics of the chains. Moreover, as the chain length was increased, a red-shift in excitations was observed. The results show that even with rather subtle structural changes in the surrounding ligands, we can produce significant effect on the properties of the materials.