Synthesis and structure of luminescent ReI(CO)3Cl complexes incorporating pyridyltriazine, pyrazinyltriazine and triazolopyridine chelation

The triazine and triazolo ligands (general abbreviations, L) used in the present work are pyridyltriazine (L-1), pyrazinyltriazine (L-2) and triazolopyridine (L-3), respectively. The reaction of Re(CO)(5)Cl with a slight excess of L in boiling benzene has furnished complexes of the type Re(CO)(3)Cl(L). In dichloromethane solution the complexes display a band of moderate intensity in the visible region: Re-I (CO)(3)Cl(L-1), 433 nm; Re-I(CO)(3)Cl(L-2) 451 nm and Re-I(CO)(3)(L-3) 440 nm. This band is tentatively assigned to a pi(Re) --> pi*(L) MLCT excitation. The solutions are also fluorescent, the emission peaks lying at 679, 671 and 592 nm, respectively. The fluorescence is believed to originate from the (MLCT)-M-3 state. The quantum yield in the three cases are 5.6 x 10(-4), 5.5 x 10(-4) and 0.036, respectively. Interestingly the L 3 complex is comparable with Ru(bpy)(3)(2+) with regard to quantum yield. The IR and H-1 NMR spectra of the chelates are reported. The complexes are electroactive in acetonitrile solution wherein an irreversible one-electron anodic oxidation (1.30-1.50 V) is observed cyclic voltammetrically. The X-ray structures of the L-1 and L-3 complexes have been determined revealing distorted octahedral ReC3N2Cl coordination spheres. The carbon monoxide ligands are facially disposed. In both complexes the chelate rings make a satisfactory plane (mean deviation 0.03 angstrom). The average Re-N, Re-C and Re-Cl lengths are unexceptional. (C) 2006 Elsevier Ltd. All rights reserved.