An oxorhenium(V) Schiff-base complex: Synthesis, characterisation, structure, spectroscopic and electrochemical aspects

Reaction of equimolar proportion of trans-ReOCl3(PPh3)2 with HL, a 1:1 Schiff-base condensate of salicylaldehyde and allylamine, in chloroform gives rise to ReO(L)(PPh3)Cl2 1a in optimal yield. 1a has been characterized by C, H and N microanalyses, ESI-MS, FT-IR, UV–Vis spectra, molar conductivity measurements. The X-ray crystal structure of 1a reveals that it is an octahedral cis-Cl,Cl oxorhenium(V) complex. The rhenium center is in ‘NO2Cl2P’ coordination sphere. 1a crystallizes in the orthorhombic space group Pna21 with a = 17.3541(11), b = 10.2737(6), c = 15.2113(10) Å, V = 2712.0(3) Å3 and Z = 4. The photophysical and electrochemical aspects of 1a have been studied. Electrochemical studies in dichloromethane show Re(V) to Re(VI) oxidation at 1.437 V along with a reduction of Re(V) to Re(IV) at −0.705 V versus Ag/AgCl. Excitation of 1a in chloroform at 460 nm leads to a fluorescent emission at 525 nm with a quantum yield (Ф) of 0.17. Geometry optimization of the cis-Cl,Cl complex 1a vis-à-vis its trans analogue, trans-Cl,Cl complex 1b, have been performed at the level of the density functional theory (DFT). It is revealed that 1b is more stable than 1a by 4 kcal per mole of energy in gas phase.