Synthesis, characterization and antioxidant evaluation of metal complexes derived from a dianil ligand with a flexible linkage: anomalous magnetic behavior of the nickel complex

The synthesis and characterization of N,N 0 -bis (1-naphthaldimine)-p-oxydianiline, H2L, and its Zn(II), Cu(II), Ni(II) and Co(II) complexes are reported. Single crystal X-ray structural analysis showed that H2L consists of two tautomers where the central diphenylether unit is flanked by either two ketoamino forms or by one ketoa- mino and one enolimino form. Physico-chemical data revealed the formation of non-electrolytic (M2L2(2H2O)n)� mH2 O( n and m = 0-2) complexes with variable geome- tries. The nickel complex exhibited anomalous magnetic behavior compared to literature analogues. This result is attributed to molecular association and suggests the exis- tence of both planar and octahedral forms in a conforma- tional equilibrium. These complexes exhibit thermal stability up to 700 C, except for the Ni(II) complex which degraded to its oxide. Antimicrobial screening data showed that H2L had no efficacy against a panel of pathogenic microorganisms, whereas the Ni(II) complex exhibited potency both as an antibacterial and antifungal agent. The properties of the complexes with respect to DPPH radical scavenging, acetyl cholinesterase inhibition and antihe- molytic activity were evaluated.