Novel Mn(III) heterochelates: synthesis, thermal, spectroscopic, and coordination aspects

This article describes the synthesis, structural features, and thermal studies of novel Mn(III) heterochelates of the type [Mn(SB (n) )(L)(H2O)]center dot xH(2)O [H2SB (n) = Nicotinic acid [1-(3-methyl-5-oxo-1-phenyl-4,5 dihydro-1H-pyrazol-4yl)-acylidene]-hydrazide where acyl = acetyl (H2SB1); benzoyl (H2SB2); propionyl (H2SB3); buteryl (H2SB4); phenyl acetyl (H2SB5); and HL = 5-Chloro-7-iodo-8-hydroxyquinoline (clioquinol)]. The heterochelates have been characterized on the basis of elemental analyses, magnetic susceptibility measurements, cyclic voltammetric studies, (FTIR and electronic) spectra, and thermal studies. The FAB mass spectrum of [Mn(SB1)(L)H2O]center dot 3H(2)O has been carried out. The cyclic voltammetric studies reveal that quasi-reversible reduction process of Mn(III)/Mn(II) coupled system suggesting that the ligands readily destabilize higher oxidation states of metal ion. Kinetic parameters such as order of reaction (n) and the energy of activation (Ea) were calculated using Freeman-Carroll method. The pre-exponential factor (A), the activation entropy (S*), the activation enthalpy (H*), and the free energy of activation (G*) were calculated using Horowitz-Metzger equations.