Optical, electrochemical and structural studies of the first rhenium compound of di-2-pyridylketone benzoylhydrazone (dpkbz) fac-Re(CO)3(dpkbh)Cl

The reaction between Re(CO)5Cl and di-2-pyridylketone benzoylhydrazone (dpkbh) in refluxing toluene gave fac-Re(CO)3(dpkbh)Cl in good yield. Spectroscopic and electrochemical measurements on fac-Re(CO)3(dpkbh)Cl revealed strong solvent–solute interaction, as manifested by the sensitivity of its reduction potentials and electronic absorption spectra to solvent variations. Spectroscopic and thermo-optical measurements in polar solvents in the presence of NaBH4 and NaBF4, or NaOH and citric acid reveal reversible interconversion between the low- and high-energy electronic states of fac-Re(CO)3(dpkbh)Cl at 440 and 318 nm. Electrochemical measurements on fac-Re(CO)3(dpkbh)Cl show irreversible redox processes pointing to electrochemical transformations following the first electronic transfer(s). Crystals of fac-Re(CO)3(dpkbh)Cl obtained from an acetonitrile solution of fac-Re(CO)3(dpkbh)Cl are centric and crystals of fac-Re(CO)3(dpkbh)Cl·dmso obtained from a dmso solutions of fac-Re(CO)3(dpkbh)Cl are acentric. Structural studies show non-identical twins of fac-Re(CO)3(dpkbh)Cl and fac-Re(CO)3(dpkbh)Cl·dmso with distorted octahedral coordination about rhenium and the conformation about the amide group is syn- in fac-Re(CO)3(dpkbh)Cl and anti- in fac-Re(CO)3(dpkbh)Cl·dmso. The packing of molecules shows a web of hydrogen bonds that may account for the stability of different conformations observed in the solid state.