Tridentate Schiff base coordinated trigonal bipyramidal / square pyramidal copper(II) complexes: Synthesis, crystal structure, DFT / TD-DFT calculation, catecholase activity and DNA binding

Using tridentate O,N,O/N,N,O donor Schiff bases and 1,10-phenanthroline, five coordinated copper(II) complexes, {[Cu(L1)(phen)][Cu(L1)(phen)]∙5H2O}(1) and {[Cu(L2)(phen)](ClO4)}(2) [H2L1 = 3-[(2-hydroxy-benzylidene)-amino]-propionic acid, HL2 = 2-methoxy-6-[(3-methylamino-propylimino)-methyl]-phenol, phen = 1,10-phenanthroline] have been synthesized and structurally characterized. Complex 1 is a co-crystal, where two geometrically different (trigonal bipyramidal (TBP) and square pyramidal (SP)) complexes of same compositions [Cu(L1)(phen)] are within a unit cell. Complex 2 exhibits a trigonal bipyramidal geometry and counter balanced by perchlorate anion. In solid state, complex 1 contains both SP and TBP geometries, but theoretical calculation reveals that in solution it exists only in one form with SP geometry. DFT/TD-DFT calculations for the complexes were performed to explain the structures and electronic spectral properties of the complexes. Both the complexes are active for catalytic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butylquinone (3,5-DTBQ) in presence of molecular oxygen and the calculated values of turnover numbers are 62 ± 3 and 52 ± 3 h−1 for 1 and 2, respectively. Interactions of complexes with calf thymus-DNA have been studied using fluorescence spectroscopic techniques and the calculated values of binding constants are (2.20 ± 0.06) × 104 and (2.27 ± 0.07) × 104 L mol−1 for complexes 1 and 2, respectively.