Spectroscopic, thermal, non-isothermal decomposition kinetics and quantum chemical computational studies of Ni(II)- and Cu(II)-Schiff base complexes

Herein we report spectroscopic, thermal, non-isothermal decomposition kinetics and theoretical studies of two mononuclear Ni(II)- and Cu(II)-complex of general formula [M(L)(H2O)]center dot xH(2)O; {M = Ni(II) & Cu(II)} derived from tridentate 2,4-dichloro-6-{[(5-chloro-2-sulfanylphenyl)imino]methyl}phenol ligand (H2L). These compounds were synthesized and characterized by various physicochemical and spectral techniques. Thermal decomposition of complexes was studied in four steps at different temperature regions to understand the degradation pattern of complexes under nitrogen atmosphere up to 1073 K at the 10 K min(-1) heating rate. The non-isothermal kinetic parameters viz. activation energy (E*), pre-exponential factor (Z), entropy of activation (Delta S*), enthalpy of activation (Delta H*) and free energy of activation (Delta G*) of degradation process were calculated using Coats-Redfern (C-R), Piloyan-Novikova (P-N) and Horowitz-Metzger (H-M) methods assuming first order degradation and proposing a random nucleation mechanism of thermal decomposition. Quantum chemical computational investigations were carried out at the B3LYP level using 6-31G basis set. The calculated harmonic vibrations were compatible with the observed FTIR and Raman frequencies. The thermodynamic properties (C (p,m) A degrees; S (m) A degrees and H (m) A degrees) with varying temperatures up to 500 K and non-linear optical properties were also evaluated at the same level of theory.