Synthesis, structural, spectral studies, and DFT calculations of a series of mixed ligand complexes of a tridentate N, N, S pyrazole based aldimine and 2,2'-bipyridine. The first example of structurally characterized dimeric cadmium(II) adduct with unusual μ2-Osulfonamido bridges

Abstract Refluxing of equimolar amounts of 2,2'-bipyridine (bipy) and N, N, S-tridentate basic form of the Schiff base N-[2-[[3-methyl-1-phenyl-5-thioxo-pyrazole-4-ylidenemethyl]amino]phenyl]-4-methylbenzenesulfonamide (H2L) with corresponding metal acetate hydrate (Cu, Ni, Zn, Cd) in acetonitrile-methanol solution (1:1) give rise to the formation of mononuclear mixed ligand complexes with a common formula [M(L)bipy]·(CH3CN) (M = Cu(II), Ni(II), Zn(II)) (1-3) and binuclear cadmium(II) heteroleptic compound with the composition [Cd2(L)2(bipy)2]·(CH3CN)2(CH3OH)2 (4). All compounds were characterized by C, H, N elemental analysis, FT-IR, 1H NMR, and magnetic measurements. The structures of the ligand H2L and complexes 1, 3 and 4 were determined by X-ray single-crystal diffraction. The metal center in 1, 3 is surrounded with imine and amide nitrogen, sulfur of thiol group of H2L and two nitrogen of 2,2'-bipy employing as the auxiliary ligand. The crystal structure of binuclear cadmium complex reveals unexpected μ2-O sulfonamido bridges. The time-dependent density functional theory (TD-DFT) calculations have been performed to explore the assignment and the nature of the bands in experimental UV-vis absorption spectra of adducts 1-4.