engleski

The study of pyridine adducts of VO(acac)2 in the solid state and solution

Formation of adducts between oxovanadium(IV) diketonates and Lewis bases is well documented [1]. The Lewis bases coordinate on sixth coordination site of the vanadium atom either in trans- or cis- position relative to the oxygen of vanadyl . The position in which the Lewis base is coordinated depends on the basicity and steric effect of the Lewis base [2]. In this study we have investigated formation of adducts between bis(pentane-2, 4-dionato)oxovanadium(IV) (VO(acac)2) and a series of pyridine derivatives in the solid state and solution. The stability constants of the adducts were determined by means of spectrophotometric titrations. The corresponding stability constants were correlated with the Hammett substituent coefficients and pKa values of the pyridine derivatives. Crystal structures of eight adducts were determined and it was found that in the solid state the pyridine, 3-methylpyridine and 4-methylpyridine formed trans- adducts with VO(acac)2, whereas in the case of 4-benzoylpyridine adduct the pyridine derivative is in cis-position, 2-amino-3-methylpyridine and 2-amino-5-methylpyridine also formed trans- adducts in addition of creating N-H...O hydrogen bond via pyridine amino group and chelate ring of complex. In case of 2, 4, 6-trimethylpiridine and 2-amino-6-methylpyridine, molecule of water was coordinated on VO(acac)2 and formed hydrogen bonds with 2 molecules of neighbouring pyridine molecules. It was found that the stereochemistry of the coordinated species (cis/trans) present in the solid state depends on the basicity of the Lewis base and it is reflected in the characteristic UV-spectra of the adducts.

adducts ; , crystal structure ; oxovanadium(IV) ; spectrophotometry

nije evidentirano