Molecular structure and spectroscopic studies on novel complexes of coumarin-3-carboxylic acid with Ni(II), Co(II), Zn(II) and Mn(II) ions based on density functional theory

Novel Ni(II), Co(II), Zn(II) and Mn(II) complexes of coumarin-3-carboxylic acid (HCCA) were studied at experimental and theoretical levels. The complexes were characterised by elemental analyses, FT-IR, 1H NMR, 13C NMR and UV–Vis spectroscopy and by magnetic susceptibility measurements. The binding modes of the ligand and the spin states of the metal complexes were established by means of molecular modelling of the complexes studied and calculation of their IR, NMR and absorption spectra at DFT(TDDFT)/B3LYP level. The experimental and calculated data verified high spin Ni(II), Co(II) and Mn(II) complexes and a bidentate binding through the carboxylic oxygen atoms (CCA2). The model calculations predicted pseudo octahedral trans-[M(CCA2)2(H2O)2] structures for the Zn(II), Ni(II) and Co(II) complexes and a binuclear [Mn2(CCA2)4(H2O)2] structure. Experimental and calculated 1H, 13C NMR, IR and UV–Vis data were used to distinguish the two possible bidentate binding modes (CCA1 and CCA2) as well as mononuclear and binuclear structures of the metal complexes.

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► Formation of novel Ni(II), Zn(II), Co(II), Mn(II) complexes of coumarin-3-carboxylic acid.
► Experimental and theoretical study of the geometrical and electronic structures.
► Relation between IR, NMR, absorption spectroscopic data and metal complex geometry.
► Bidentate coumarin binding to the transition metals through the carboxylic oxygens.
► Prediction of pseudo octahedral Zn, Ni, Co complexes and a binuclear Mn complex.