Cis-trans isomerism in cobalt(II) complexes with 3-hydroxypicolinic acid. Structural, DFT and thermal studies |
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Authors: | Boris-Marko Kukovec Ivan Kodrin Krešimir Furi? |
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Institution: | a Laboratory of General and Inorganic Chemistry, Department of Chemistry, Faculty of Science, University of Zagreb, Horvatovac 102a, HR-10000 Zagreb, Croatia b Laboratory of Organic Chemistry, Department of Chemistry, Faculty of Science, University of Zagreb, Horvatovac 102a, HR-10000 Zagreb, Croatia c Molecular Physics Laboratory, Division for Material Physics, Ru?er Boškovi? Institute, POB 180, Bijeni?ka cesta 54, HR-10002 Zagreb, Croatia |
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Abstract: | Pyridine and 4-picoline cobalt(II) complexes with 3-hydroxypicolinic acid, Co(3-OHpic)2(py)2], (2), and Co(3-OHpic)2(4-pic)2], (3), were prepared, their molecular and crystal structures were determined by X-ray structure analysis and their thermal stability by TGA/DTA methods. Complex 2 appears only as trans isomer and 3 as cis isomer. Based on DFT calculations, the most significant effect on orientation of (un)substituted ligands around cobalt, i.e.cis-trans isomerism, comes from crystal packing. Theoretical calculations show that exchange of methyl group in pyridine does not affect relative stability of one monomer unit, i.e.cis isomer is for about 1 kcal mol−1 more stable than trans isomer. Hydrogen bonds of the O-H···O type are present only as intramolecular ones in the crystal structures of 2 and 3, while intermolecular C-H···O hydrogen bonds and π-π stacking interactions (π-π interactions present only in 3) assemble molecules in 3D architecture. Interactions between two monomer units in crystal packing could be separated and theoretically investigated to calculate interaction energy. In our case, both non-hypothetical models, i.e.trans isomer of 2 and cis isomer of 3, show more favorable interaction energies than hypothetical ones, i.e.cis isomer of 2 and trans isomer of 3, for the same type of interaction. |
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Keywords: | Cobalt(II) complexes 3-Hydroxypicolinic acid Cis-trans isomers Weak intermolecular interactions DFT calculations Thermal methods (TGA/DTA) |
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