Département de chimie moléculaire

Car-Parrinello mol. dynamics (CMPD) simulations and static computations are reported at the BLYP level of d. functional theory (DFT) for mixed [LaClx(H2O)y(MeCN)z]3-x complexes in aq. and nonaq. soln. (acetonitrile). Both methodologies predict coordination nos. (i.e., x + y + z) that are successively lower than nine as the Cl content increases from x = 0 to 3. While the static DFT method with implicit solvation through a polarizable continuum model overestimates the binding strength of chloride and erroneously predicts [LaCl2(H2O)5]+ as global free-energy min., constrained CPMD simulations with explicit solvent and thermodn. integration reproduce the weak binding of chloride in water reasonably well. Special attention is called to the dipole moments of coordinated water mols. as function of coligands and solvent, evaluated through maximally localized Wannier function centers along the CPMD trajectories. Cooperative polarization of these water ligands by the metal cation and the surrounding solvent is remarkably sensitive to fluctuations of the La-O distances and, to a lesser extent, on the La-water tilt angles. The mean dipole moment of water ligands is rather insensitive to the other coligands, oscillating around 3.2 D, 3.5 D, and 3.3 D in MeCN, water, and [dmim]Cl soln., resp., the latter being an archetypical ionic liq. [on SciFinder(R)]