Synthesis, characterization and molecular sensing capability of fac-[Re(CO) 3(κ 2-N,N-dpktsc)Cl] where dpktsc = di-2-pyridylketone thiosemicarbazone

Abstract

When di-2-pyridyl ketone thiosemicarbazone (dpktsc) was allowed to react with [Re(CO) 5Cl] in toluene under reflux, fac-[Re(CO) 3(κ 2-N,N-dpktsc)Cl] was isolated in good yield. The identity of fac-[Re(CO) 3(κ 2-N,N-dpktsc)Cl] was established from the results of its elemental analysis, spectroscopic, and electrochemical properties. The infrared spectra of fac-[Re(CO) 3(κ 2-N,N-dpktsc)Cl] show the facial coordination of the carbonyl groups, and the pyridyl N,N-coordination of dpktsc. 1H NMR measurements on fac-[Re(CO) 3(κ 2-N,N-dpktsc)Cl] in d 6-dmso and d 6-acetone confirmed the pyridyl N,N-coordination of dpktsc, and showed strong solvent dependence as manifested by the sensitivity of thioamide and ammine protons to their surroundings. The electronic absorption spectra of fac-[Re(CO) 3(κ 2-N,N-dpktsc)Cl] in protophilic solvents (dmso and dmf) display two intra-ligand charge transfer (ILCT) transitions at 476 and 360 nm and in non-protophilic solvents a single ILCT transition at 346 nm in CH 3CN and 342 nm in CH 2Cl 2. Reversible interconversion between fac-[Re(CO) 3(κ 2-N,N-dpktsc)Cl] and its conjugate base was established in protophilic solvents using a base to shift the equilibrium to the conjugate base and an acid to shift the equilibrium or conjugate base to the neutral form. Substrates in concentrations as low as 1 × 10 −10 M can be detected and determined using protophilic solutions of fac-[Re(CO) 3(κ 2-N,N-dpktsc)Cl]. When MCl 2 (M = Zn, Cd or Hg) was allowed to interact with fac-[Re(CO) 3(κ 2-N,N-dpktsc)Cl] in protophilic solvents, the intensity of the low energy ILCT band disappeared and a shift in the high energy ILCT electronic transition was observed that hints to the coordination of MCl 2 to fac-[Re(CO) 3(κ 2-N,N-dpktsc)Cl]. Electrochemical measurements on fac-[Re(CO) 3(κ 2-N,N-dpktsc)Cl] in dmf showed sequential irreversible redox processes in accord with the electrochemical reduction or oxidation of the thiosemicarbazone moiety.