Synthesis, Characterization, and Density Functional Theory Investigation of the Solid-State [UO(2)Cl(4)(H(2)O)](2–) Complex

[Image: see text] 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.