M{κ2S,S-S2C-piperazine-C2H4N=C(R)}n] {Co(III), Ni(II), Cu(II) or Zn(II)} complexes bearing pendant Schiff base moieties: spectral characterization, fluorescence, cyclic voltammetric and TGA/DTA study

Abstract

A series of neutral mononuclear complexes [M{κ2S,S-S2C-piperazine-C2H4N=C(R)}n] {R = Ph; M = Co(III) 1, Ni(II) 2, Cu(II) 3, Zn(II) 4; R = Naph; M = Co(III) 5, Ni(II) 6, Cu(II) 7, Zn(II) 8; n = 2 for 2–4, 6–8 and n = 3 for 1, 5} bearing pendant Schiff base moieties were synthesized through self-assembly involving N-[phenylmethylidene]-2-piperazin-1-ylethanamine (L1) or N-[naphthylmethylidene]-2-piperazin-1-ylethanamine (L2) with two equivalents each of CS2 and corresponding metal acetates. The complexes 1–8 were characterized by microanalysis, ESI-MS, IR, 1H, 13C NMR, DEPT 135, UV–visible absorption, and emission spectroscopy. Complexes 1, 3, and 8 exhibit fluorescence emissions at 342, 344, and 348 nm upon excitation at 273 (for 1 and 3) and 263 (for 8) with concomitant Stokes shifts of 69, 71, and 85 nm. The spectral and magnetic moment data support octahedral geometry around Co(III) and square planar/tetrahedral geometry around other metal centers. Thermal stabilities of 1–8 have been investigated by thermogravimteric analysis. The cyclic voltammograms clearly suggest that the complexes exhibit electroreduction principally associated with pendant imine moieties except Cu(II) complex 7 which displays quasi-reversible reduction corresponds to the Cu(II)/Cu(I) redox couples, in addition to reversible electroreduction of pendant imine groups associated with the coordinated ligands.