Synthesis, characterization and structure of the first rhenium compound of di-2-pyridyl ketone thiophene-2-carboxylic acid hydrazone (dpktah), fac-[Re(CO) 3( N, N-κ 2-dpktah)Cl

Abstract

fac-[Re(CO) 3(κ 2- N, N -dpktah)Cl], isolated from the reaction between [Re(CO) 5Cl] and di-2-pyridyl ketone thiophene-2-carboxylic acid hydrazone (dpktah) in refluxing toluene, exhibits rich physico-chemical properties. The formulation of fac-[Re(CO) 3(κ 2- N, N -dpktah)Cl] was established from the results of its elemental analysis and spectroscopic measurements, and confirmed using X-ray crystallography. The 1H NMR spectrum of fac-[Re(CO) 3(κ 2- N, N-dpktah)Cl] revealed the coordination of dpktah and exchange of the amide proton. Electronic absorption measurements show two intra-ligand charge transfer transitions (ILCT) and established inter-conversion between fac-[Re(CO) 3(κ 2- N, N-dpktah)Cl] and its conjugate base. Thermo-optical studies confirmed the facile inter-conversion between fac-[Re(CO) 3(κ 2- N, N-dpktah)Cl] and its conjugate base. Optosensing measurements show [MCl 2] (M = Zn, Cd or Hg) in concentrations as low as 1.00 × 10 −7 M can be detected and determined using protophilic solutions of fac-[Re(CO) 3(κ 2- N, N-dpktah)Cl]. X-ray structural analysis done on a single crystal of fac-[Re(CO) 3(κ 2- N, N-dpktah)Cl] confirmed its identity and divulge two symmetry-independent molecules in the asymmetric unit. The supramolecular structure of fac-[Re(CO) 3(κ 2- N, N-dpktah)Cl] disclosed anti-parallel chains locked via a network of hydrogen bonds. Non-classic hydrogen bonds of the type C–H…Cl connect molecules in the chain and classic hydrogen bonds of the type N–H…O connect adjacent chains.