Lattice Solvent and Crystal Phase Effects on the Vibrational Spectra of UO₂Cl₄^2–

Abstract

We present the structural and spectroscopic characterization of six uranyl tetrachloride compounds along with a quantified analysis showing the influence of both the crystallographic phase and the lattice solvent upon the vibrational properties of the uranyl moiety. From the uranyl symmetric and asymmetric stretching frequencies we use a valence bond potential model to calculate the stretching and interaction force constants of the uranyl moiety in each compound. Quantifying these second-sphere influences provides insight into the vibrational properties, and indirectly the electronic structure, of the uranyl ion in its ground state. These data provide a better guide for assessing the validity of future comparisons with respect to bond strength, length, and electronic properties among series of actinyl compounds where non-actinide variables may be at play.

Detection and identification of solids, surfaces, and solutions of uranium using vibrational spectroscopy

“…Careful evaluation of the uranyl tetrachloro system, which has been thoroughly characterized in solution and in 18 solid-state coordination compounds, provides us with an excellent platform to understand these effects. Schnaars and Wilson [125] systematically studied [UO 2 Cl 4 ] 2− complex crystallized with the tetraphenylphosphonium/tetraphenylarsonium cation and various solvent molecules. The ν 1 mode was shown to be independent of solvent composition and tetraphenylarsonium cation presence.…”

“…Two polymorphs formed with either a triclinic ( P -1) cell (838 cm −1 ) or a monoclinic form (823 cm −1 ). Schnaars and Wilson [125] hypothesized that the 15 cm −1 difference in the symmetric stretching band arose from either 1) additional hydrogen bonding to the uranyl oxo in the monoclinic form or 2) subtle differences in the UACl bond lengths that would lead to an increased electrostatic effect and uranyl bond destabilization. Qu et al demonstrated similar effects by crystallizing the uranyl tetrachloro species with imidazolium cations [126].…”

Equatorial coordination of uranyl: Correlating ligand charge donation with the Oyl-U-Oyl asymmetric stretch frequency

“…5 However, understanding the underlying basis for the effects of coordinating ligands on uranium-oxygen bonding in uranyl is complicated by the many competing and uncertain interactions in condensed phases. 6 Accordingly, Groenewold, Van Stipdonk and coworkers 7 employed infrared multiphoton dissociation (IRMPD) spectroscopy of isolated gas-phase uranyl-ligand (L) complexes, UO 2 (L) n…”

Structure and bonding in crystalline cesium uranyl tetrachloride under pressure

“…[1][2][3][4][5][6][7][8] The nature of the chemical bonding in Cs 2 UO 2 Cl 4 was deeply studied by Zhurov et al 3,4 using experimental X-ray diffraction electron densities. [5][6][7]9 In the experimental work of Schnaars and Wilson, 6,7 it was observed that Badger's rule 10 fails for actinyl complexes since a shorter distance is not always accompanied by a higher stretching force constant. X-ray diffraction and infrared and Raman spectroscopy have also been used to investigate how stretching frequencies correlate with U-O bond lengths in a variety of uranyl chloro complexes with emphasis on the evaluation of force (k 1 ) and interaction (k 12 ) constants involved in the UO 2 moiety.…”

“…[5][6][7]9 In the experimental work of Schnaars and Wilson, 6,7 it was observed that Badger's rule 10 fails for actinyl complexes since a shorter distance is not always accompanied by a higher stretching force constant. 2,[5][6][7][8]12 In spite of the strong nature of the U-O multiple bond, small but meaningful variations of its bond length could be observed under the pressure conditions attained in diamond anvil cell experiments. 5 It is to be concluded that 'a great deal of caution must be afforded .…”