Synthesis, spectroscopic characterization and thermal behavior of metal complexes formed with N′-(1-(4-hydroxyphenyl) ethylidene)-2-oxo-2-(phenylamino) acetohydrazide (H3OPAH)

Complexes of Co(II), Ni(II), Cu(II), Mn(II), Cd(II), Zn(II), Hg(II) and U(IV)O22+ with N′-(1-(4-hydroxyphenyl) ethylidene)-2-oxo-2-(phenylamino) acetohydrazide (H3OPAH) are reported and have been characterized by various spectroscopic techniques like IR, UV–visible, 1H NMR and ESR as well as magnetic and thermal (TG and DTA) measurements. It is found that the ligand behaves as a neutral bidentate, monoanionic tridentate or tetradentate and dianionic tetradentate. An octahedral geometry for [Mn(H3OPAH)2Cl2], [Co2(H2OPAH)2Cl2(H2O)4] and [(UO2)2(HOPAH)(OAc)2(H2O)2] complexes, a square planar geometry for [Cu2(H2OPAH)Cl3(H2O)]H2O complex, a tetrahedral structure for [Cd(H3OPAH)Cl2], [Zn(H3OPAH)(OAc)2] and [Hg(H3OPAH)Cl2]H2O complexes. The binuclear [Ni2(HOPAH)Cl2(H2O)2]H2O complex contains a mixed geometry of both tetrahedral and square planar structures. The protonation constants of ligand and stepwise stability constants of its complexes at 298, 308 and 318 K as well as the thermodynamic parameters are being calculated. The bond lengths, bond angles, HOMO, LUMO and dipole moments have been calculated to confirm the geometry of the ligand and the investigated complexes. Also, thermal properties and decomposition kinetics of all compounds are investigated. The interpretation, mathematical analysis and evaluation of kinetic parameters (Ea, A, ΔH, ΔS and ΔG) of all thermal decomposition stages have been evaluated using Coats–Redfern and Horowitz–Metzger methods.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Preparation of ligand and its metal complexes. ► Characterization of prepared complexes. ► Spectral, thermal, magnetic and ESR studies. ► pH-metric study.