engleski

Synthesis, X-ray structural, IR spectroscopic, thermal and DFT studies of nickel(II) and copper(II) complexes with 3-methylpicolinic acid. UV/Vis spectrophotometric study of complexation in the solution

Complexes [Ni(3-Mepic)2(H2O)2] (1) and [Cu(3- Mepic)2(H2O)] • H2O (2) were prepared by the reaction of the respective metal salts and 3- methylpicolinic acid (3-MepicH) in the aqueous solution. Recrystallization of [Cu(3-Mepic)2(H2O)] • H2O (2) from 3-picoline (3-pic) afforded [Cu(3- Mepic)2(3-pic)] (3). The copper(II) ion has square-pyramidal coordination environment in both 2 and 3, achieved by two N, O-bidentate 3- methylpicolinate ligands and by a water molecule (2) or 3-picoline molecule (3) in the apical position of the pyramid. Thermogravimetric studies showed the initial loss of two coordinated water molecules in 1 and one 3-picoline molecule in 3. UV/Vis spectrophotometry confirmed the existence of Cu(II)-3-MepicH complex (metal-to-ligand ratio of 1:2) and a mixture of two Ni(II)-3-MepicH complexes (metal-to-ligand ratios of 1:2 and 1:3) in the diluted aqueous solutions. The computational model B3LYP/6-311G(d, p) showed the best reproducibility for one monomer unit geometry of 2 and 3. The calculated and experimental IR spectra of 2 and 3 were compared and characteristic bands assigned. The calculations showed a preference for octahedral geometry over the square-pyramidal. The reversed preference for square-pyramidal geometry, determined in the crystal structure of 2 and 3, was illustrated by modeling stabilizing interactions in simplified dimer model.

nickel(II) ; copper(II) ; 3-methylpicolinic acid ; UV/Vis spectrophotometry ; DFT calculations ; crystal structure

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