Ab initio Quantum Chemical Study on Charge Distribution and Molecular Structure of Uranyl (VI) Species with Raman Frequency

Abstract

Ab initio molecular orbital calculation was performed for uranyl (VI) monomer and dimer complexes with some water molecules and/or hydroxide ions. The Raman active frequencies were calculated for each complex after structural optimization in vacuum state, and investigated the molecular structure and the charge distribution. For uranyl monomer, the calculated Raman frequencies for uranyl with 5 or 6 water molecules show good agreement with experimental Raman frequencies for uranyl hydrates. On the contrary, the calculation underestimates the Raman frequency in case of hydroxide ions in uranyl complex. 4+ , and the theoretical Raman frequency and uranyl bond lengths have the good coincidence with those of experiments. The calculated uranyl bond length of dimer is slightly longer than that of monomer. Also, the charge of oxygen atom in uranyl shows larger change than that of uranium atom between dimer and monomer. And this charge distribution is mostly influenced by the charge donation of ligands. If only same ligands are surrounding, the number of ligands influenced this charge distribution.

Computationally-Guided Assignment of Unexpected Signals in the Raman Spectra of Uranyl Triperoxide Complexes

“…Computational models, most commonly density functional theory (DFT), have improved the understanding of uranium speciation in aqueous solution and consequently the fate of uranium in the environment. − The accuracy of these models, however, is contingent on comparisons of predictions to experimentally determined parameters for structurally simple and pure phases. In this regard, uranyl peroxides present a unique and sometimes complex family of inorganic compounds spanning structures ranging from mono- and oligomeric species to nanoscale capsules containing as many as 124 uranyl polyhedra. − These materials are of interest because of their potential application in an advanced nuclear fuel cycle and possible role in the transport of actinides in the environment. − Their ease of preparation and high purity as well as the presence of Raman-active vibrational modes make these materials good candidates for evaluation of the aforementioned empirical and computational models.…”

Hierarchy of Pyrophosphate-Functionalized Uranyl Peroxide Nanocluster Synthesis

“…Metal-oxide clusters are a group of discrete, macromolecular materials with potential applications in diverse fields such as single-molecule catalysis, surface chemistry, and biology. − The advancement of this field, driven by nearly two centuries of scientific exploration, resulted in the description of structures ranging from simple Lindqvist, Keggin, and Dawson types to exotic sphere-, wheel-, and hedgehog-shaped polyoxometalates (POMs). − Consequently, examination of these systems provided grounds for development of structure–property relationships and design of task-specific molecules. − Actinide peroxide nanoclusters represent a relatively new subclass of POMs that are interesting due to their importance in advanced nuclear fuel cycles and for understanding the environmental mobility of actinides. , Their finite and nanoscale nature provides unique opportunities for development and validation of computational models used in the fields of geo- and actinide chemistry. − Extreme radiation fields, such as those present during a nuclear reactor failure, can potentially lead to formation of sufficient amounts of peroxide (via α-radiolysis of water) to support self-assembly of actinide peroxide nanoclusters. , Since their discovery in 2005, more than 60 unique actinide peroxide nanoclusters have been published. , …”

Tailoring single-ion magnet properties of coordination polymer C11H18DyN3O9 (Dy-CP) using the radial effective charge model (RECM) and superposition model (SPM)

“…This suggests that the magnetic relaxation occurs via the first and second excited states. The additional energy required for relaxation via the second excited state 31,93,94 may be contributed by the external dc magnetic field B Z 0.3 T. 44 A parameter is defined as de = (D 0-2 À D 0-1 )/D 0-1 , which also describes the axiality of the g-tensors and SIM behaviour: 31 for the fieldinduced SIMs, de varies within 0.8-16, while for the zero-field SIMs, de varies within 12-44. 31 The parameter for Dy-CP is calculated: de = 1.41, which falls within the range for the fieldinduced SIMs.…”

“…The obtained Z i of oxygens in Dy-CP matches with the Mulliken charges (within the range: −0.13 to −0.43) calculated using ab initio study for oxygen ions in some uranyl monomer and dimer complexes coordinated to water and OH − groups. 94 The average effective charge of oxygens: is much reduced compared to the valence charge of −2, implying large covalency of oxygen ions. 58,69 An inversely proportional relation exists between D r and Z i , expressed as 73,80 where the factor f depends on the coordination number and nature of the coordinated ligand atom.…”