The thermochromic behavior exhibited by vanadium(IV) alkoxides, [V2(μ-OPr i)2(OPr i) 6] and [V2(μ-ONep)2(ONep)6 ], OPr i = isopropoxide and ONep = neopentoxide, was studied by molecular modeling using DFT, TDDFT and INDO/S methods. The vibrational and electronic spectra calculated for [V2(μ-OPr i)2(OPr i) 6] were very similar to the experimental data registered for crystalline samples of the complex and for its solutions at low temperature (< 210 K), while spectra recorded at high temperature (> 315 K) were compatible with those calculated for the monomeric form, [V(OPr i)4]. These results consistently point to a monomer/dimer equilibrium as an explanation for the solution thermochromism of {V(OPr i)4}n. In spite of the structural similarity between [V2(μ-ONep)2(ONep)6 ] and [V2(μ-OPr i)2(OPr i) 6] in the solid state, the thermochromic behavior of the former could not be explained by the same model, and the possibility of tetranuclear aggregation at low temperatures was also investigated.

Recentemente Galabov and Bobadova-Parvanova mostraram que a energia de formação da ligação de hidrogênio obtida por cálculo no nível HF/6-31G(d,p) está altamente correlacionada com o potencial eletrostático molecular na região aceptora em alguns compostos carbonílicos simples. Neste trabalho mostramos que o potencial eletrostático pode ser substituído pela energia de Koopmans. A correlação entre esta energia e a energia de formação da ligação de hidrogênio é tão alta quanto aquela observada por Galabov e Bobadova-Parvanova. O potencial de Siegabhn relacionando às energias de Koopmans e cargas GAPT mostra que a energia de ligação de hidrogênio não está simplesmente correlacionada com a carga da região aceptora pois as cargas dos átomos vizinhos são também importantes no processo de ligação de hidrogênio.

Recently Galabov and Bobadova-Parvanova have shown that the energy of hydrogen bond formation calculated at the HF/6-31G(d,p) level is highly correlated with the molecular electrostatic potential at the acceptor site for a number of simple carbonyl compounds. Here it is shown that the electrostatic potential can be replaced by Koopmans' energy. The correlation between this energy and the hydrogen bond formation energy is just as high as the one observed by Galabov and Bobadova-Parvanova. The Siegbahn simple potential relating Koopmans' energies and GAPT charges shows that the hydrogen bond energy is not simply correlated with the charge of the acceptor site because the charges on the neighboring atoms are also important in the hydrogen bonding process.