Ruthenium monoterpyridine complexes with 2,6-bis(benzoxazol-2-yl)pyridine as an ancillary ligand: Synthesis, structure and spectral studies

Ruthenium monoterpyridine complexes, [1](+) and [2](+), with 2,6-bis(benzoxazol-2-yl)pyridine as an ancillary ligand, L, have been synthesized and characterized by UV-Vis, FT-IR and H-1 NMR spectroscopic techniques. The formulations of the complexes were confirmed by the single crystal structure of their perchlorate salts. In both complexes, the Ru-II center is hexa-coordinated in a distorted geometry. In complex [1](+), the ancillary ligand L behaves as a bidentate ligand: in [2](2+), however, it binds the metal center as a tridentate ligand. The central pyridine nitrogen of terpyridine (N-p,N-trpy) is in a cis position with respect to the central pyridine nitrogen of the ancillary ligand (N-p,N-benz) in complex [1](+) and in a trans-position in complex [2](2+). The cis orientation of N-p,N-trpy and N-p,N-benz in complex [1](+) forces L to behave as bidentate. The quasi-reversible Ru-II/Ru-III couple appears at 0.90 and 1.44 V versus SCE in the case of complex [1](+) and [2](2+), respectively. [1](+), in the presence of aqueous AgNO3, affords [2](2+) through an intramolecular dissociative interchange pathway. (C) 2008 Elsevier Ltd. All rights reserved.