Synthesis, Characterization, and Density Functional Theory Investigation of the Solid-State [UO₂Cl₄(H₂O)]^2– Complex

Abstract

A significant number of solid-state [UO 2 Cl 4 ] 2− coordination compounds have been synthesized and structurally characterized. Yet, despite their purposive relative abundance in aqueous solutions, characterization of aquachlorouranium(VI) complexes remain rare. In the current study, a solid-state uranyl aqua chloro complex ((C 4 H 12 N 2 ) 2 [UO 2 Cl 4 (H 2 O)]Cl 2 ) was synthesized using piperazinium as a charge-balancing ligand, and the structure was determined using single-crystal X-ray diffraction. Using periodic density functional theory, the electronic structure of the [UO 2 Cl 4 (H 2 O)] 2− complex was compared to [UO 2 Cl 4 ] 2− to uncover the strengthening of the U�O bond in [UO 2 Cl 4 (H 2 O)] 2− . Changes in the strength of the U�O bond were validated further with Raman and IR spectroscopy, where uranyl symmetrical (ν 1 ) and asymmetrical (ν 3 ) stretches were blue-shifted compared to the reference [UO 2 Cl 4 ] 2− complex. Furthermore, the formation energy of the solid-state (C 4 H 12 N 2 ) 2 [UO 2 Cl 4 (H 2 O)]Cl 2 complex was calculated to be −287.60 ± 1.75 kJ mol −1 using isothermal acid calorimetry. The demonstrated higher stability relative to the related [UO 2 Cl 4 ] 2− complex was related to the relative stoichiometry of the counterions.

Three-Dimensional Noncovalent Interaction Network within [NpO2Cl4]2– Coordination Compounds: Influence on Thermochemical and Vibrational Properties

“… When there are more than one neptunyl center in the unit cell ( Z > 1), our calculations demonstrate the presence of several Np=O stretching bands emerging from the in-phase and out-of-phase vibration of neptunyl centers. However, while we could see these multiple bands experimentally, it was difficult to discern whether they were the product of coupling or an impurity, so we chose the neptunyl band with the highest intensity for our analysis . To assess the impact of NCIs on ν 1 , we calculated the sum of bond orders (BO sum ″yl″ ) of all NCIs of a single axial oxygen using eq where the BO i ″yl″ is the bond order of NCIs through the axial oxygen calculated by the DDEC6 method. − Strong hydrogen bonding interactions have previously been found to have BOs ranging from 0.07 to 0.130; therefore, this value will be used as a guide when comparing NCIs in neptunyl complexes. BO sum ″ yl ″ = ∑ i O yl ··· normalH / normalM BO i ″ yl ″ …”

Synthesis, characterization, and density functional theory investigation of (CH6N3)2[NpO2Cl3] and Rb[NpO2Cl2(H2O)] chain structures

“…At higher concentrations ([Cl − ] > 13 M), saturation of the halide ion is achieved within the equatorial plane to create the [AnO 2 Cl 4 ] 2−/3− or [AnO 2 Cl 4 (H 2 O)] 2−/3− species. 2,6–9…”

“…Discrete U( vi ), Np( vi ), and Np( v ) tetrachloro complexes have all been structurally characterized with a range of charge balancing cations, and they are widely used as synthons for crystal engineering or as model systems in the study of Non-Covalent Interactions (NCIs) in hybrid materials. 8–16 Within the aquachloro complexes, only the [UO 2 Cl 2 (H 2 O) 3 ], 17 [C 4 H 12 N 2 ] 2 [UO 2 Cl 4 (H 2 O)]Cl 2 8 and [NMe 4 ][NpO 2 Cl(H 2 O) 4 ]Cl 18 coordination compounds have been synthesized and structurally characterized using X-ray diffraction techniques. These aquachloro structural building units have also been observed within extended 1-D chain topologies ( e.g.…”