Alkynyl-Iminopyridine-Based Trinuclear Ni(II), Zn(II), Cd(II), and Cu(II) Complexes: Structural, Electrochemical, Luminescence and Nonlinear Optical Properties.

A new series of alkynyl-functionalized trinuclear metal complexes, with the general formula [M₃(L/L)(Cl)₆] (M = Ni(II), Zn(II), Cd(II), Cu(II)), were synthesized using alkynyl-functionalized iminopyridine ligands L and L. The complexes were characterized by various techniques, including FTIR, NMR, ESI-MS, UV-Vis, ESR, TGA, PXRD, and SEM. All synthesized complexes exhibit absorption in the visible region, primarily attributed to metal-to-ligand charge transfer (MLCT) and intra-ligand charge transfer (ILCT) transitions. Electrochemical investigations of the Ni(II) and Cu(II) analogues reveal quasireversible redox behavior. EPR spectral analysis of the Cu(II) complexes indicates a significant degree of covalency in the metal-ligand interactions. All complexes emit red luminescence at room temperature. The second harmonic generation (SHG) efficiency, evaluated via the Kurtz powder technique, highlights the potential of these complexes as promising candidates for nonlinear optical (NLO) applications.