Synthesis, Characterization, and Sensitizing Properties of Heteroleptic Ru II Complexes Based on 2,6‐Bis(1‐pyrazolyl)pyridine and 2,2′‐Bipyridine‐4,4′‐dicarboxylic Acid Ligands

Starting from the Ru(bpp)Cl 3 precursor ( 1 ), a family of novel heteroleptic Ru II complexes of the general formulae [Ru(bpp)(dcbpyH)(X)] [X = Cl – ( 2a ), NCS – , ( 3 )] and Na[Ru(bpp)(dcbpy)(CN)] ( 4 ) with the ligands 2,6‐bis(1‐pyrazolyl)pyridine (bpp) and 2,2′‐bipyridine‐4,4′‐dicarboxylic acid (dcbpyH 2 ) has been synthesized, spectroscopically characterized, and attached to nanocrystalline TiO 2 electrodes to be tested as solar cell sensitizers. Addition of HCl to ( 2a ) led to the corresponding cationic derivative [Ru(bpp)(dcbpyH 2 )Cl]Cl ( 2b ). All complexes were characterized by FT‐IR, FT‐Raman, UV/Vis, 1 H NMR spectroscopy, elemental analysis, and mass spectrometry. Complex 4 and the previously reported [Ru(bdmpp)(dcbpyH 2 )Cl](PF 6 ) ( 5 ) [bdmpp is 2,6‐bis(3,5‐dimethyl‐1‐pyrazolyl)pyridine] were characterized by single‐crystal X‐ray diffraction. The photo‐electochemical properties of the dyes 2 – 4 were investigated and the efficiency of the corresponding dye‐sensitized solar cells was compared to the sensitizing performance of the cis ‐[Ru(dcbpyH) 2 (NCS) 2 ](NBu 4 ) 2 ( N719 ) dye.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)