Investigations of the Cobalt Hexamine Uranyl Carbonate System: Understanding the Influence of Charge and Hydrogen Bonding on the Modification of Vibrational Modes in Uranyl Compounds

Abstract

Hydrogen bonding networks within hexavalent uranium materials are complex and may influence the overall physical and chemical properties of the system. This is particularly true if hydrogen bonding takes places between the donor and the oxo group associated with the uranyl cation (UO 2 2+ ). In the current study, we evaluate the impact of charge-assisted hydrogen bonding on the vibrational modes of the uranyl cation using uranyl tricarbonate [UO 2 (CO 3 ) 3 ] 4– interactions with [Co(NH 3 ) 6 ] 3+ as the model system. Herein, we report the synthesis and structural characterization of five novel compounds, [Co(NH 3 ) 6 ]Cl(CO 3 ) ( Co_Cl_CO 3 ), [Co(NH 3 ) 6 ] 4 [UO 2 (CO 3 ) 3 ] 3 (H 2 O) 11.67 ( Co4U3 ), [Co(NH 3 ) 6 ] 3 [UO 2 (CO 3 ) 3 ] 2 Cl (H 2 O) 7.5 ( Co3U2_Cl ), [Co(NH 3 ) 6 ] 2 [UO 2 (CO 3 ) 3 ]Cl 2 ( Co2U_Cl ), and [Co(NH 3 ) 6 ] 2 [UO 2 (CO 3 ) 3 ]CO 3 ( Co2U_CO 3 ), which contain differences in the crystalline packing and extended hydrogen bonding networks. We show that these slight changes in the supramolecular assembly and hydrogen bonding networks result in the modification of modes as observed by infrared and Raman spectroscopy. We use density functional theory calculations to assign the vibrational modes and provide an understanding about how uranyl bond perturbation and changes in hydrogen bonding interactions can impact the resulting spectroscopic signals.

Periodic Density Functional Theory Calculations of Uranyl Tetrachloride Compounds Engaged in Uranyl–Cation and Uranyl–Hydrogen Interactions: Electronic Structure, Vibrational, and Thermodynamic Analyses

“…12 These second-sphere NCIs, including Coulombic, hydrogen bonding, and halogen bonding, can influence the overall chemical and physical properties of the material, 12 including structural topologies, 13 redox potentials, 14 , 15 and activation of vibrational modes. 16 − 18 …”

“…The binding of these equatorial ligands leads to additional electron donation to the An­(VI) metal center and weakening of the UO yl bond, an effect often observed through red-shifting of the ν 1 and ν 3 modes in Raman and IR spectroscopy. − UO yl bond weakening is known to increase the Lewis basicity of the axial oxo groups, enhancing their ability to interact with Lewis acids through different non-covalent interactions (NCIs) . These second-sphere NCIs, including Coulombic, hydrogen bonding, and halogen bonding, can influence the overall chemical and physical properties of the material, including structural topologies, redox potentials, , and activation of vibrational modes. − …”

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

“…The actinyl tetrachloride system has previously been utilized as a model system due to its ability to form a range of solid-state compounds with high reproducibility. 10,13,15,16,21 This system has been widely utilized by the Cahill group to develop rational approaches to the design of U(VI) hybrid materials and to explore NCIs. In addition, Cahill et al conducted preliminary investigations into the thermochemical properties of actinyl systems and their correlation with NCIs.…”

“…Furthermore, perturbation of the An=O bond by NCIs has been shown to result in red-shifting of the symmetrical stretch (ν 1 ) and the activation of additional vibrational bands. 13,15,18 However, a systematic evaluation of the relationship between NCIs and overall stability and vibrational characteristics has not been conducted, particularly for Np(VI), due to the inherent difficulties in working with transuranic materials.…”

“…6,9,10 Strong An=O bonding reduces the Lewis basicity of the axial oxygen, 11 but the equatorial ligands increase electron density at the An center, weakening the An=O bond 11,12 and promoting a range of NCIs. The interaction between the actinyl oxo and neighboring groups can be classified into various forms, including actinyl−cation (ACIs), 13,14 actinyl−hydrogen (AHIs), 15,16 actinyl−halogen (AXIs), 10,12 and actinyl−actinyl interactions (AAIs). 17 ACIs, AHIs, and AXIs are found in both hexa-and pentavalent species; however, AAIs are more common in pentavalent species.…”