Synthesis and spectroscopic studies of homo-binuclear, alkoxo bridged homo- and hetero-tetranuclear metal complexes of a bis-N2O4 Schiff base ligand derived from ethanolamine and macroacyclic tetranaphthaldehyde

Three new homo-binuclear Ni(II), Cu(II), Zn(II) complexes (2–4), homo-tetranuclear Cu(II) complex (5), and hetero-tetranuclear Cu(II)–Ni(II) complex (6) of a macroacyclic potentially bis-hexadentate N2O4 Schiff base have been synthesized. The imino-alcohol ligand, H4L was obtained by the condensation of ethanolamine with 2,2′-[2,3-bis(1-formyl-2-naphthyloxymethyl)-but-2-ene-1,4-diyldioxy]bis(naphthalene-1-carbaldehyde). The structures of both the Schiff base and its complexes have been proposed by elemental analyses, spectroscopic data i.e. IR, 1H and 13C NMR, UV–vis, electrospray ionisation mass spectra, molar conductivities and magnetic susceptibility measurements. The ligand has two similar compartments to bind first primary two metal ions, and acts bi- or tetra-negative, bis-tetradentate forming five membered chelate ring. However, secondary two metal ions (either Cu2+ or Ni2+) are ligated with dianionic oxygen atoms of the alcohol groups and are linked to the 1,10-phenanthroline-nitrogen atoms in the tetranuclear complexes (5 and 6).

Graphical abstractThree new homo-binuclear Ni(II), Cu(II), Zn(II) complexes (2–4), homo-tetranuclear Cu(II) complex (5), and hetero-tetranuclear Cu(II)–Ni(II) complex (6) of a macroacyclic potentially bis-hexadentate N2O4 Schiff base have been described and discussed. The structures of the Schiff base and its complexes have been proposed by elemental analyses, spectroscopic data, i.e. IR, 1H and 13C NMR, UV–vis, electrospray ionisation mass spectra, molar conductivities and magnetic susceptibility measurements.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► 2-{[2-(4-{1-[(2-Hydroxy-ethylimino)-methyl]-naphthalen-2-yloxy}-2,3-bis-{1-[(2-hydroxy-ethylimino)-methyl]-naphthalen-2-yloxymethyl}-but-2-enyloxy)-naphthalen-1-ylmethylene]-amino}-ethanol, H4L, (1) was obtained from the reaction of 2,2′-[2,3-bis(1-formyl-2-naphthyloxymethyl)-but-2-ene-1,4-diyldioxy]bis(naphthalene-1-carbaldehyde) and ethanol amine. ► Homo-binuclear complexes (2–4) were prepared by reacting M(ClO4)2·6H2O [M = Cu(II), Ni(II) and Zn(II)] with the Schiff base ligand, H4L. ► Homo- and hetero-tetranuclear complexes (5,6) were prepared by binding of secondary two metal ions (either Cu2+ or Ni2+) to dianionic oxygen atoms of binuclear Cu(II) complex and 1,10-phenanthroline-nitrogen atoms. ► The structures of all the synthesized compounds were confirmed by the spectroscopic techniques. A detailed assignment of the spectra and the electrochemical behavior were proposed.