The effect of the functional, basis set and solvent in the simulation of the geometry and spectroscopic properties of VIVO2+ complexes. Chemical and biological applications

The geometry of 32 (VO2+)-O-IV complexes with different donor set, electric charge, geometry, arrangement of the ligands with respect to the V-O bond and type of ligand was calculated by density functional theory methods. 32 V-O, 45 V-O, 16 V-OH, 40 V-N, 24 V-S, and 14 V-Cl bonds were examined. The performance of several functionals (B3LYP, B3P86, B3PW91, HCTH, TPSS, PBE0, and MPW1PW91), keeping constant the Pople triple-zeta basis sets 6-311g, was tested. The order of accuracy of the functional in the prediction of the bond distances, expressed in terms of mean of the deviation ?d (?d = dcalcd - dexptl) and absolute deviation vertical bar?d vertical bar (vertical bar?d vertical bar = vertical bar dcalcd - dexptl vertical bar) from the experimental values and of the corresponding standard deviations (SD(?d) and SD(vertical bar?d vertical bar)), is: B3P86 similar to PBE0 similar to MPW1PW91 > B3PW91 >> TPSS > B3LYP >> HCTH. In the gas phase the prediction of V-O, V-O, V-N bond lengths is rather good, but that of V-OH, V-S and V-Cl distances is by far worse. An improvement in the optimization of V-S and V-Cl lengths is reached by adding polarization and diffuse functions on the sulfur and chlorine atoms. Finally, a general improvement in the prediction of all the calculated bond lengths and angles is obtained by simulating the structures in the solvent where they are isolated within the framework of the polarizable continuum model. The last choice allows also to improve the prediction of structural (the deviation of a penta-coordinate geometry toward the trigonal bipyramid) and spectroscopic parameters (51V and 14N hyperfine coupling constants and 14N nuclear quadrupolar coupling constant). In most of the cases, the structures optimized in solution closely approach the experimental ones and this can be of great help in the simulations of naturally occurring vanadium compounds and metal site of V-proteins, like amavadin and the reduced form of vanadium bromoperoxidase (VBrPO).