Département de chimie moléculaire

Optimizations at the BLYP and B3LYP levels are reported for the mixed uranyl chloro/water/acetonitrile complexes [UO2Cln(H2O)x(MeCN)5-n-x]2-n (n = 1-3) and [UO2Cln(H2O)x(MeCN)4-n-x]2-n (n = 2-4), in both the gas phase and a polarizable continuum modeling acetonitrile. Car-Parrinello mol. dynamics (CPMD) simulations have been performed for [UO2Cl2(H2O)(MeCN)2] in the gas phase and in a periodic box of liq. acetonitrile. According to population analyses and dipole moments evaluated from maximally localized Wannier function centers, uranium is less Lewis acidic in the neutral UO2Cl2 than in the UO22+ moiety. In the gas phase the latter binds acetonitrile ligands more strongly than water, whereas in acetonitrile soln., the trend is reversed due to cooperative polarization effects. In the polarizable continuum the chloro complexes have a slight energetic preference for water over acetonitrile ligands, but several mixed complexes are so close in free energy $Δ$G that they should exist in equil., in accord with previous interpretations of EXAFS data in soln. The binding strengths of the fifth neutral ligands decrease with increasing chloride content, to the extent that the trichlorides should be formulated as four-coordinate [UO2Cl3L]- (L = H2O, MeCN). Limitations to their accuracy notwithstanding, d. functional calcns. can offer insights into the speciation of a complex uranyl system in soln., a key feature in the context of nuclear waste partitioning by complexant mols. [on SciFinder(R)]