Phenoxo bridged luminescent dinuclear zinc(II) and cadmium(II) complexes of 2-[[[2-(2-pyridyl)ethyl]imino]methyl]phenol: Crystal structure, photophysical and thermal studies

Reactions of zinc(II) and cadmium(II) halides with an N,N,O-donor Schiff-base ligand HL (obtained by the 1:1 condensation of salicylaldehyde and 2-(2-aminoethyl)pyridine) yield six new phenoxo bridged dinuclear complexes of the general formula [Zn2L2X2] (1–3) and [Cd2L2X2] (4–6), where X = Cl, Br and I, respectively. The complexes have been characterized by routine physicochemical techniques: elemental analyses, IR, electronic spectral studies, conductivity and solid state thermal studies. Complexes 1, 2 and 6 have further been characterized by single crystal X-ray structural analyses. The ligands, as well as all six complexes, are highly fluorescent. For the ligand, the emission band is attributed to a p–p⁄ transition, whereas for the complexes the emissions may be assigned to ligand-to-metal charge transfers (LMCT). Quantum yield calculations revealed that the metal complexes exhibit more intense fluorescence compared to the ligand, which is supposed to be due to the enhancement of rigidity of the ligand on chelation, which reduces the loss of energy through non-radiative channels of the intraligand emission excited state. Thermogravimetric analyses of the complexes suggest that upon heating the thermally stable final product in the case of complexes 1–3 is ZnO, 6 gives CdO, whereas for complexes 4 and 5 the final product remains unidentified.