Impact of substituents on the metal-based redox potential for a series of complexes based on trans-[Cl(pyridine) 4 Ru-L] + where L is a para-substituted derivative of cyanobenzene Laura M. Fischetti, Meghan M. Gordon, Michael R. Reardon, and Cliff J. Timpson Roger Williams University, One Old Ferry Road, Bristol, Rhode Island Abstract Over the past four years, a number of studies in our group have been aimed at exploring the photochemical and electrochemical properties of monomeric and dimeric complexes based on trans-[Cl(pyridine) 4 Ru-L] +. Our current efforts involve the continued synthesis, characterization, and study of a series of monomeric complexes of the type trans-[Cl(pyridine) 4 Ru-L] + where L is a para- substituted cyanobenzene derivative, NCArCOOH, NCArCOMe, NCArCHO, NCArBr, NCArCl, NCArNH 2, NCArOH, NCArCH 3, and NCArCN. The work presented here will detail our efforts to prepare and to purify each of the complexes. Correlations between the metal-based E 1/2 values and the electron donating or withdrawing effects of the substituents will be discussed. Methods and Materials Spectroscopic grade solvents (Aldrich) and reagents (Aldrich) were obtained commercially and used as supplied. All reactions were conducted under an argon atmosphere and were shielded from ambient light. The complex trans-[ClRu(py) 4 (NO)](PF 6 ) 2 was prepared according to procedures previously reported by Coe.2,3 Column chromatography was carried out using silica gel 60 ( mesh) (Aldrich) with varying proportions of acetone:dichloromethane (5% to 50% acetone) as the eluent. All products were dried at room temperature in a vacuum dessicator for a minimum of 24 h before use. UV-Vis spectra and kinetic data were collected on a Hewlett-Packard HP-8453 Diode Array spectrophotometer. Infrared data was collected on a Perkin-Elmer 1600 series FT-IR, and cyclic voltammetric measurements were obtained using a Bio-Analytical Systems (BAS) CV-50W. Acknowledgments LMF, MMG and MRR gratefully acknowledge: Kate Dedeian, Hannah Nandor and Steve Hira for the synthesis of trans-[Ru(py) 4 Cl(NO)](PF 6 ) 2 Financial support from the RWU Undergraduate Student Research Grant CJT gratefully acknowledges: Financial support from a grant from the RWU Faculty Research Foundation References 1. Zakeeruddin, S.M.; Nazeeruddin, M.K.; Pechy, P.; Rotzinger, F.P.; Humphry-Baker, R.; Kalyanasundaram, K.; Gratzel, M. Inorg. Chem., 1997, 36, Coe, B.J.; Meyer, T.J.; White, P.S. Inorg. Chem., 1993, 32, Coe, B.J.; Meyer, T.J.; White, P.S. Inorg. Chem., 1995, 34, Juris, A.; Campanga, S.; Balzani, V.; Belser, P.; von Zelewsky, A. Coord. Chem. Rev., 1988, 84, Balzani, V.; Scandola, F. Supermolecular Photochemistry; Wiley, Chinchester, UK, Carol, F.A. Perspectives on Structure and Mechanism in Organic Chemistry. First ed. Brooks Cole: 1997; Introduction Over the past four years, a number of studies have been aimed at exploring the photochemical and electrochemical properties of monomeric and dimeric complexes based on trans-[Cl(pyridine) 4 Ru-L] +. The reason for this attention is the ability of the ruthenium polypyridyl to function as an efficient photosensitizer in photovoltaic devices. 1-4 In the course of these studies, researchers have come to appreciate the critical role molecular geometry plays in the operation of these devices. This research will explore the chemistry of trans-[Cl(pyridine) 4 Ru-L] + as potential building blocks for larger oligomeric complexes which could possibly exhibit interesting photochemical and/or redox active properties. 5 The trans-geometry of the tetrapyridine ruthenium monomer, combined with appropriate bridging ligands, should ultimately allow fabrication of supramolecular complexes that exhibit linear or pseudo-linear geometries. 3 Spectroscopic Properties of Complexes Complexλ max, nmAssignment trans-[Cl(py) 4 Ru(MeCN)]PF dπ to π* (py) 355 dπ to π* (L) trans-[Cl(py) 4 Ru(ArCN)]PF dπ to π* (py) 351 dπ to π* (L) trans-[Cl(py) 4 Ru(NCArCHO)]PF dπ to π* (py) 329 dπ to π* (L) trans-[Cl(py) 4 Ru(NCArCOMe)]PF dπ to π* (py) 316 dπ to π* (L) trans-[Cl(py) 4 Ru(NCArCOOH)]PF 6 285dπ to π* (py) 376dπ to π* (L) trans-[Cl(py) 4 Ru(NCArCl)]PF 6 249dπ to π* (py) 398dπ to π* (L) trans-[Cl(py) 4 Ru(NCArNH 2 )]PF 6 249dπ to π* (py) 397 dπ to π* (L) trans-[Cl(py) 4 Ru(NCArCN)]PF 6 244dπ to π* (py) 347dπ to π* (L) trans-[Cl(py) 4 Ru(NCArOH)]PF 6 247dπ to π* (py) 399dπ to π* (L) trans-[Cl(py) 4 Ru(NCArCH 3 )]PF 6 242dπ to π* (py) 358dπ to π* (L) Synthetic Scheme Electrochemical & Infrared Properties of Complexes ComplexE 1/2 mV v Ag-AgCl IR(cm -1 ) trans-[Cl(py) 4 Ru(ArCN)]PF 6 995* 2200 (moderate) trans-[Cl(py) 4 Ru(NCArCHO)]PF (strong) trans-[Cl(py) 4 Ru(NCArCOMe)]PF (moderate) trans-[Cl(py) 4 Ru(NCArCOOH)]PF (weak) trans-[Cl(py) 4 Ru(NCArBr)]PF trans-[Cl(py) 4 Ru(NCArCl)]PF (weak) trans-[Cl(py) 4 Ru(NCArNH 2 )]PF trans-[Cl(py) 4 Ru(NCArCN)]PF (moderate) trans-[Cl(py) 4 Ru(NCArOH)]PF (strong) trans-[Cl(py) 4 Ru(NCArCH 3 )]PF (strong) *converted from v SCE OHNH 2 Cl CH 3 H Br CHO COOH COCH 3 CN NH 2 OHCl CH 3 H Br CHO COOH COCH 3 CN