Non-covalent interactions of uranyl complexes: a theoretical study

Abstract

We report a set of theoretical calculations designed to examine the potential of model uranyl complexes to participate in hydrogen- and halogen-bonding. Potential energy scans for the interaction of [UO2Cl2(H2O)3] and [UO2(NCSe)2(H2O)3] with a single water molecule demonstrate that uranyl is a weak hydrogen bond acceptor, but that equatorially coordinated water is a strong hydrogen bond donor. These predictions are supported by a survey of contacts reported in the Cambridge Structural Database. At the minima of each scan, we show that the interaction energy is only weakly dependent on the choice of the theoretical method, with standard density functional theory methods comparing well with coupled-cluster, MP2 and double-hybrid DFT predictions. Geometry optimisation of a 1 : 1 uranyl : water complex results in a cyclic structure, in which vibrational frequencies, atoms-in-molecules and natural bond orbital analysis support the weakness of U-Oyl as an acceptor. The origin of this behaviour is traced to the electronic structure of uranyl, and in particular covalency in the U-Oyl bonds resulting from donation into formally empty 5f and 6d orbitals on U.

Structural, Spectroscopic, and Computational Analysis of Halogen- and Hydrogen-Bonding Effects within a Series of Uranyl Fluorides with 4-Halopyridinium

“…10,11,42 Since compounds 1−5* are not all isostructural, direct trends cannot be noted regarding the shifts in the U�O symmetric stretches. Within category (ii), however (2, 3, 5*), which share a C 1 site symmetry at the Qualitatively, the most significant donor → acceptor NBO pairs are π(U�O) → σ*(C−X) and LP(X) → π*(U�O), a charge-transfer (CT) picture that comports well with the literature 43 on noncovalent interactions involving the uranyl moiety (Figure 14 and Tables S2 and S3). As the %vdW overlap between the halogen and O yl increases from F to Cl to I (Table 2) 43 not nearly large enough to singlehandedly cause the steady decrease in the energy of the ν 1i vibrational mode.…”

“…Within category (ii), however (2, 3, 5*), which share a C 1 site symmetry at the Qualitatively, the most significant donor → acceptor NBO pairs are π(U�O) → σ*(C−X) and LP(X) → π*(U�O), a charge-transfer (CT) picture that comports well with the literature 43 on noncovalent interactions involving the uranyl moiety (Figure 14 and Tables S2 and S3). As the %vdW overlap between the halogen and O yl increases from F to Cl to I (Table 2) 43 not nearly large enough to singlehandedly cause the steady decrease in the energy of the ν 1i vibrational mode. One must be mindful that the interaction between a cationic Xpyridinium and an anionic uranyl fluoride is dominated not by charge transfer but by Coulombic attraction and is thus charge-assisted.…”

“…4−5 kcal/ mol). Putting this in the context of the work done by Platts and Baker on the weakness of the X•••O yl interactions, the strongest of the above-mentioned CT-type interactions can be classified as a borderline weak/moderate halogen bond;43 not nearly large enough to singlehandedly cause the steady decrease in the energy of the ν 1i vibrational mode. One must be mindful that the interaction between a cationic Xpyridinium and an anionic uranyl fluoride is dominated not by charge transfer but by Coulombic attraction and is thus charge-assisted.…”

Structural and Computational Investigation of Halogen Bonding Effects on Spectroscopic Properties within a Series of Halogenated Uranyl Benzoates

“…Thus, establishing a synthetic technique to reproducibly generate structurally related materials with variable substituents is necessary and has been explored for f-elements through a “cap and link” strategy. , Systematic studies have utilized N-donor “capping” ligands to prevent oligomerization of metal centers and promote a single species with a desired and consistent coordination environment, while peripheral halogen atoms assemble units through noncovalent interactions. Through this technique and broader computational efforts, , recent studies have found that those terminal “yl” oxygen atoms are actually quite accessible to incoming highly polarizable halogens atoms (e.g., bromine, iodine), ,, as well as other interactions to promote specific reactivity and properties. − Further, these systematic approaches allowed for the elucidation of uranyl spectroscopic trends driven by ligand inductive effects at the uranyl equatorial plane versus halogen interaction participation at the “yl” oxygen …”

Structural and computational characterization of a bridging zwitterionic-amidoxime uranyl complex

“…This distortion in AAO-1 also results in hydrogen bonding between the AO ligands and the uranyl oxygens. hydrogen bonding to the uranyl oxygens has frequently been of interest [46][47][48][49][50][51][52] although hydrogen bonding to the uranyl oxygens are generally accepted as weak hydrogen bond acceptors. To further evaluate the role of the noncoordinating water, a minimization of an AAO analogue of 1 with a water molecule (AAO-H 2 O-1) was carried out ( Figure 6B).…”