Three new mono–di–trinuclear cobalt complexes of selectively and non-selectively condensed Schiff bases with N2O and N2O2 donor sets: Syntheses, structural variations, EPR and DNA binding studies

Three new mono–di–trinuclear cobalt complexes of three different Schiff bases have been synthesised. In all the three complexes psuedohalides (NCO− and N3−) have been incorporated to generate structural variation. Of the three Schiff bases, HL1 and HL2 were obtained by selective condensation of two different 1,3-diamines with 2-hydroxyacetophenone and H2L3 resulted from non-selective condensation of 1,3-diamine with 2-hydroxyacetophenone. Only one –NH2 functionality of 1,3-diaminopropane and 1,3-diaminopentane was selectively condensed with 2-hydroxyacetophenone to generate Schiff bases HL1 and HL2, respectively. H2L3 was obtained by condensing both the amine functionality of 1,3-diaminopropane with 2-hydroxyacetophenone. Therefore HL1 and HL2 behave as a N2O donors, whereas H2L3 provides a N2O2 donor coordination environment for the cobalt ions in the respective complexes. In [Co(L1)2]2 [Co(NCO)4] (1) the asymmetric unit comprises of five mononuclear cobalt centers, [Co2(μ–N3)2(L2)2(N3)2] (2) is a dinuclear and [(H2O)2Co(μ–N3)2(μ–L3)2Co2(N3)1.25(CH3O)0.75] · H2O (3) is a trinuclear cobalt species. The three complexes have been characterised using IR, UV–Vis spectroscopy and cyclic voltammetry. Structural aspects of 1, 2 and 3 have been described by performing single crystal X-ray analysis. EPR analyses of 1 and 3, and DNA binding abilities of all three cobalt complexes have been studied in detail.