Pisano, Luisa and Kiss, Dóra and Várnagy, Katalin and Sanna, Daniele and Micera, Giovanni and Garribba, Eugenio (2009) Potentiometric, spectroscopic and DFT study of the VIVO complexes formed by di(pyridin-2-yl) ligands. European Journal of Inorganic Chemistry, Vol. 2009 (16), p. 2362-2374. eISSN 1099-0682. Article.
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The coordinating properties of a series of di(pyridin-2-yl) derivatives towards the VIVO2+ ion have been studied through the combined application of potentiometric and spectroscopic (electronic absorption and EPR spectroscopies) methods. In particular, di(pyridin-2-yl)amine (DPA), di(pyridin-2-yl)methane (DPM), di(pyridin-2-yl) ketone (DPK), di(pyridin-2-yl)methanol (DPMO), 2-acetylpyridine (2-AP) and 2-hydroxymethylpyridine (2-HMP), and two amino acid derivatives of di(pyridin-2-yl)methylamine (DPMA), namely N-glycyl-DPMA and N-histidyl-DPMA, have been examined. The stability constants of proton and VIVO complexes (logβ) were measured at 25 °C and at a constant ionic strength of 0.2 M (KCl). The results show that the simple di(pyridin-2-yl) derivatives having only pyridine nitrogen atoms form mono-chelated species with the (Npyr, Npyr) donor set, whereas those provided with carbonyl or hydroxy groups form mono- and bis-chelated complexes with (Npyr, CO) or (Npyr, O-) coordination. The square pyramidal species with 2×(Npyr, O-) coordination exists in equilibrium with the octahedral isomer, which has an axially bound water molecule and is characterized by an anomalously low value of the 51V hyperfine coupling constant along the z-axis (Az). DFT calculations were used to optimize the geometry of the complexes and to predict the Az values measured in the EPR spectra for the penta- and hexacoordinate complexes formed by DPK, DPMO, 2-AP and 2-HMP and for the [VOLH-1]+ and[VOLH-2] species formed by the amino acid derivatives of DPMA.
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