A new luminescent sulfate bridged dimeric copper(II) complex with DNA binding and SO 2 fixation ability: Synthesis and structure

Abstract

New luminescent mononuclear and dinuclear copper(II) ( S = 1/2) complexes [Cu(HL)(H 2O) 2](ClO 4) 2 ( 1a) and [Cu 2(HL) 2(μ-SO 4) 2]·2H 2O ( 1b) were synthesized with the acyclic tridentate pyridine-2-carboxaldehyde-2-pyridylhydrazone ligand, HL ( 1). Interestingly, the mononuclear complex 1a can be converted into the disulfate bridged dimeric copper(II) complex 1b by passing freshly prepared SO 2 through the basic medium. On excitation at 290 nm, the ligand fluoresces at 364 nm due to an intraligand 1(π–π∗) transition. Upon complexation with copper(II), the emission peak is slightly blue shifted (356 nm, F/F 0 0.76 for 1a and 354 nm, F/F 0 0.89 for 1b) with a little quenching in the emission intensity. The association constants ( K ass (5.06 ± 0.004) × 10 4 for 1a and K ass (5.46 ± 0.006) × 10 4 for 1b at 298 K) and the thermodynamic parameters have been determined by UV–Vis spectroscopy. The molecular structure of the complex 1b (Cu⋯Cu 4.456 Å) has been determined by single crystal X-ray diffraction studies. The complex 1b exhibits a strong interaction towards DNA as revealed from the K b (intrinsic binding constant) 6.3 × 10 4 M −1 and K sv (Stern–Volmer quenching constant) 2.93 values.