INFLUENCE OF REMOTE LIGAND LONE PAIRS ON THE ELECTRONIC-STRUCTURE ANDSPECTRUM OF BIS(BIPYRIDINE)RUTHENIUM(II) 3,4-DIAMINO-3',4'-DIIMINO-3',4'-DIHYDROBIPHENYL - TUNING BY EXTERNAL DONORS AND ACCEPTORS

The highly solvatochromic title complex comprises a donor diaminobenze ne unit (OPDA) linked to an acceptor ruthenium benzoquinonediimine (BQ DI) unit. Hydrogen bond donor and acceptor solvents influence the exte nt to which the amino group lone pairs inject charge into the OPDA rin g. The ligand tends toward planarity when the lone pairs conjugate wit h the OPDA ring and twists when the lone pairs are removed from conjug ation by hydrogen bonding to the solvent. The electronic spectra in th ese two extreme situations are very different due to large changes in the oscillator strengths of certain transitions. Extended Huckel calcu lations with charge iteration provide a means for calculating these os cillator strengths and for providing a picture of the metal to ligand and internal OPDA to BQDI charge transfer which occurs. A ZINDO/1 geom etry optimization provides additional evidence for the model developed .