Synthesis, characterization and DNA binding studies of penta- and hexa-coordinated diorganotin(IV) 4-(4-nitrophenyl)piperazine-1-carbodithioates

Two chlorodiorganotin(IV) complexes with general formula R2SnClL (R = n-C4H9(1) and C2H5(2) and a diphenyltin(IV) derivative with general formula Ph2SnL2(3), where L = 4-(4-nitrophenyl)piperazine-1-carbodithioate ligand, were prepared and characterized by elemental analysis, Raman, FT-IR, multinuclear NMR (1H, 13C and 119Sn) and mass spectrometry. On the basis of spectroscopic data the effective coordination number of Sn atom was found five (1 and 2) and six (3) both in solution and solid state. Electrochemical, kinetic and thermodynamic parameters of complexes 1–3, interacting with DNA were evaluated by cyclic voltammetry. The linearity of the plots between the peak current (I) and the square root of the scan rate (ν1/2) indicated the electrochemical processes to be diffusion controlled. The diffusion coefficients of the free (Df) and DNA bound forms (Db), standard rate constants (ks) and charge transfer coefficients (α) were determined by the application of Randle–Sevcik, Nicholson and Kochi equations. The values of binding constant and binding site size were evaluated from voltammetric data. The results revealed the following increasing order of binding strength: 1 (5.4 × 103) < 3 (8.4 × 103) < 2 (1.24 × 104) M−1. The UV–Vis spectroscopic data also indicated the same order of binding strength. Furthermore, the binding mode was suggested on the base of shift in peak potential (CV) and absorption maxima (UV–Vis spectroscopy).