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The inverse trans influence (ITI) is investigated in uranyl, UO22+, and its isoelectronic imido (U(NH)22+) and carbene (U(CH2)22+) analogues at the density functional and complete active space self consistent field levels of theory. The quantum theory of atoms in molecules is employed to quantify, for the first time, the effect of the ITI on covalent bond character and its relationship to bond lengths and complex stability. [ABSTRACT FROM AUTHOR]

The discovery of solvates (crystal structures where the solvent is incorporated into the lattice) dates back to the dawn of chemistry. The phenomenon is ubiquitous, with important applications ranging from the development of pharmaceuticals to the potential capture of CO2 from the atmosphere. Despite this interest, we still do not fully understand why some molecules form solvates. We have employed molecular simulations using simple models of solute and solvent molecules whose interaction parameters could be modulated at will to access a universe of molecules that do and do not form solvates. We investigated the phase behavior of these model solute-solvent systems as a function of solute-solvent affinity, molecule size ratio, and solute concentration. The simulations demonstrate that the primary criterion for solvate formation is that the solute-solvent affinity must be sufficient to overwhelm the solute-solute and solvent-solvent affinities. Strong solute-solvent affinity in itself is not a sufficient condition for solvate formation: in the absence of such strong affinity, a solvate may still form provided that the self-affinities of the solute and the solvent are weaker in relative terms. We show that even solvent-phobic molecules can be induced to form solvates by virtue of a pΔV potential arising either from a more efficient packing or because of high pressure overcoming the energy penalty. [ABSTRACT FROM AUTHOR]

The electronic structures of a series of uranium hexahalide and uranyl tetrahalide complexes were simulated at the density functional theoretical (DFT) level. The resulting electronic structures were analyzed using a novel application of the Quantum Theory of Atoms in Molecules (QTAIM) by exploiting the high symmetry of the complexes to determine 5f- and 6d-shell contributions to bonding via symmetry arguments. This analysis revealed fluoride ligation to result in strong bonds with a significant covalent character while ligation by chloride and bromide species resulted in more ionic interactions with little differentiation between the ligands. Fluoride ligands were also found to be most capable of perturbing an existing electronic structure. 5f contributions to overlap-driven covalency were found to be larger than 6d contributions for all interactions in all complexes studied while degeneracy-driven covalent contributions showed significantly greater variation. σ-contributions to degeneracy-driven covalency were found to be consistently larger than those of individual π-components while the total π-contribution was, in some cases, larger. Strong correlations were found between overlap-driven covalent bond contributions, U–O vibrational frequencies, and energetic stability, which indicates that overlap-driven covalency leads to bond stabilization in these complexes and that uranyl vibrational frequencies can be used to quantitatively probe equatorial bond covalency. For uranium hexahalides, degeneracy-driven covalency was found to anti-correlate with bond stability. [ABSTRACT FROM AUTHOR]