Synthesis and physicochemical properties of fac-[Re(CO)3(κ2-N,N-dpkfah)Cl], dpkfah=di-2-pyridyl ketone 2-furoic acid hydrazone: the molecular structure of fac-[Re(CO)3(κ2-N,N-dpkfah)Cl] · acetone

Abstract

Reaction between [Re(CO)5Cl] and di-2-pyridyl ketone 2-furoic acid hydrazone (dpkfah) (1) in refluxing toluene gave fac-[Re(CO)3(κ2-N,N-dpkfah)Cl] (2). Spectroscopic and electrochemical measurements disclosed sensitivity of 2 to its surroundings. 1H-NMR measurements showed that the amide proton exchanged with solvent protons, and its chemical shift is solvent and temperature dependent, while the chemical shifts of aromatic protons are solvent and temperature independent. Electronic absorption spectra of 2 divulged two intra-ligand charge transfer transitions (ILCT) in protophilic solvents and a single ILCT transition in non-protophilic solvents. Optical measurements on protophilic solutions of 2 established an equilibrium between 2 and its conjugate base, fac-[Re(CO)3(κ2-N,N-dpkfah-H)Cl]− (3). Thermo-optical measurements confirmed that the interconversion between 2 and 3 and gave ΔG ø values of −26.48 and 22.99 kJ mol−1, respectively, for the protonation of DMF and DMSO by 2. Optosensing measurements showed that [MCl2] (M = Zn, Cd, or Hg) in concentrations as low as 1.00 × 10−7 mol L−1 can be detected and determined using protophilic solutions of 2. Electrochemical measurements showed 2 to be more stable in CH3CN than DMF. Single-crystal X-ray structural analysis on fac-[Re(CO)3(κ2-N,N-dpkfah)Cl] · acetone (4) obtained from an acetone solution of 2 confirmed the solvent–complex interaction and revealed two symmetry-independent molecules in the asymmetric unit. The extended structure of 4 disclosed parallel stacks connected via a network of classic and non-classic hydrogen bonds.