Ruthenium monoterpyridine complexes with 2,6-bis(benzimidazol-2-yl)pyridine: Synthesis, spectral properties and structure

Abstract

Ruthenium monoterpyridine complexes with the tridentate 2,6-bis(benzimidazol-2-yl)pyridine (LH2), [Ru(trpy)(LH2)](2+), [1](2+) and [Ru(trpy)(L2-)], 2 (trpy = 2,2':6',2 ''-terpyridine) have been synthesized. The complexes have been authenticated by elemental analyses, UV-Vis, FT-IR, H-1 NMR spectra and their single crystal X-ray structures. Complexes [1](2+) and 2 exhibit strong MLCT band near 475 and 509 nm, respectively, and are found to be very much dependent on solution pH. The successive pH dependent dissociations of the N-H protons of benzimidazole moiety of LH2 in [1](2+) lead to the formation of 2. The proton induced inter-convertibility of [1](2+) and 2 has been monitored via UV-Vis spectroscopy and redox features. The two pK(a) values, 5.75 and 7.70, for complex [1](2+) have been determined spectroscopically. (C) 2008