Relativistic density functional study of the dinuclear uranyl complex [(UO₂)₂(μ₂-OH)₂Cl ₂(H₂O)₄] in its crystalline environment

The hexavalent dinuclear uranyl dichloride complex [(UO₂) ₂(μ₂-OH)₂Cl₂(H₂O) ₄] was studied computationally with an all-electron scalar relativistic density functional method. This suggested hydrolysis product of uranyl in the presence of chlorine ions is one of the few polynuclear uranyl species for which a crystal structure is known. The calculated gas-phase structure is similar to the experimental crystal geometry; any major deviations are due to hydrogen bonds in the crystal. If the eight strongest hydrogen bonds are included in a model of the complex's crystalline environment, the calculated structure improves significantly. Based on this model, the hydrogen bond lengths and angles were determined, indicating that they are moderate and strong with an average binding energy of 39 kJ/mol. These computational results corroborate earlier suggestions based on experimental results concerning the location and strength of the hydrogen bonds. In addition, a valuable reference for relativistic quantum chemical methods is provided by the gas-phase results.