Synthesis of octahedral cobalt(III) complexes with mono- and di-condensed Schiff base ligands: A template-directed approach for the isolation of a rare kind of mixed-ligand complex

Two different sets of Schiff base ligands, set-1 (HL1, HL2) and set-2 (H2L3, H2L4) which have been prepared by mixing 1,3-diaminopropane and aldehydes (3-methoxy-2-hydroxybenzaldehyde or 3-ethoxy-2-hydroxybenzaldehyde) in 1:1 and 1:2 ratios, respectively, are employed for the synthesis of complexes with cobalt perchlorate. The octahedral cobalt(III) complexes of general formula [Co(L)2]ClO4 (L = L1 for complex 1, L2 for complex 1a) are obtained from the mono-condensed ligands, whereas the di-condensed ligand H2L4 results in the formation of a unique type of mixed-ligand complex [Co(L2)(L4)]ClO4 (2) where the respective di- and mono-condensed Schiff bases simultaneously coordinate to the metal center. The complexes are completely characterized by elemental analyses, IR, UV–vis spectroscopy and cyclic voltammetric studies. The structures of 1 and 2 are unequivocally established by single crystal X-ray diffraction analysis. The behavior of the Schiff base ligands during the reactions is directed by the template effect of CoIII ion modulated by the perchlorate anion present in the medium.