An oxamato bridged trinuclear copper(II) complex: Synthesis, crystal structure, reactivity, DNA binding study and magnetic properties

A linear tri-nuclear oxamato bridged copper(II) complex [Cu3(pba)(dpa)2(H2O)(ClO4)](ClO4)·H2O (1) (pbaH4 = 1,3-propanediylbis(oxamic acid), dpa = 2,2′-dipyridylamine) was isolated from the reaction mixture of Na2[Cu(pba)]·3H2O, copper perchlorate hexahydrate and dipyridylamine in methanol. On reaction with dpa or DMF in basic medium (KOH) at ambient temperature complex 1 changed to dinuclear oxalate bridged copper(II) derivatives, [Cu2(μ-C2O4)(dpa)4](ClO4)2 (2) and [Cu2(μ-C2O4)(dpa)2(DMF)2](ClO4)2 (3), respectively. The complexes 1, 2 and 3 have been characterized by physicochemical and spectroscopic tools, and also by the X-ray single crystal analysis. The hydrolysis of 1 in basic medium and thermo-gravimetric analysis has been studied. Absorption and emission spectral studies showed that complex 1 interacts with calf thymus-DNA (CT-DNA) with a binding constant (Kb) of 4.01 × 104 M−1 and linear Stern–Volmer quenching constant (Ksv) of 6.9 × 104. A strong anti-ferromagnetic interaction with a coupling constant JCuCu of 320.0 ± 0.3 cm−1 was observed from the study of magnetic behavior of complex 1 in the temperature range of 2–300 K. Electrochemical equivalency of three copper(II) ions in 1 was identified by getting only one quasi reversible cyclic voltammogram.