A new trans-dioxorhenium(V) complex with 4-aminopyridine: synthesis, structure, electrochemical aspects, DFT, and TD-DFT calculations

Abstract

The reaction of 1 : 4.4 M proportion of cis-[ReO2I(PPh3)2] and 4-aminopyridine (ampy) in acetone–water gives trans-[ReO2(ampy)4]I·2H2O (1a) in 85% yield. 1a has been characterized by C, H, and N microanalyses, FT-IR, UV–vis, 1H NMR spectroscopy, and molar conductivity. The X-ray crystal structure of 1a reveals an octahedral trans dioxorhenium(V) complex with a “N4O2” coordination for rhenium. 1a has an orthorhombic space group C2221 with a = 17.576(4), b = 19.370(4), c = 15.730(4) Å, V = 5355(2) Å3, and Z = 8. Geometry optimization of the trans-O,O complex, 1a and its cis-O,O analog, 1b performed at the level of density functional theory reveal that 1a is more stable than 1b by 25 kcal M–1 in the gas phase. The electronic spectrum of 1a was also analyzed at the level of time-dependent density functional theory. Excitation of 1a in methanol at 450 nm leads to a fluorescent emission at 505 nm with a quantum yield (Ф) of 0.04. Electrochemical studies of 1a in acetonitrile show a quasi-reversible Re(V) to Re(VI) oxidation at 0.618 V versus Ag/AgCl. This redox potential matches with the calculated redox potential of 0.621 V versus Ag/AgCl.