The electronic structure of diatomic nickel oxide.

The nature of the Ni-O bond is relevant to catalytic and environmental applications. The vibrational frequency and electronic structure of NiO were calculated using CASSCF, icMRCI+Q, CCSD(T), and DFT. CASSCF predicted a quintet state (5Σ-) ground state for the equilibrium bond distance with a state crossing at 1.65 Å, where the triplet (3Σ-) state becomes of lower energy. These states arise from the 3d8(3F)4s2 (3F) and 3d9(2D)4s1 (3D) configurations of Ni. The icMRCI+Q method predicts a triplet (3Σ-) ground state and does not predict a state crossing with the quintet. This state has significant ionic character with the 2pz of O bonding with the 4s/3dz2 of the Ni to form a σ bond. The NiO frequency at the icMRCI+Q level of 835.0 cm-1 is in excellent agreement with experiment; the value of re is 1.5992 Å at this computational level. CCSD(T) predicts ωe = 888.80 cm-1 when extrapolated to the complete basis set limit. Frequencies predicted using CCSD(T) deviate from experiment consistent with the calculations showing large multireference character. A wide array of density functionals were benchmarked. Of the 43 functionals tested, the ones that gave the best prediction of the frequency are ωB97XD, CAM-B3LYP, and τ-HCTH with respective values of 831.8, 838.3, and 837.4 cm-1 respectively. The bond dissociation energy (BDE) of NiO is predicted to be 352.4 kJ mol-1 at the Feller-Peterson-Dixon (FPD) level in good agreement with one of the experimental values. The calculated BDEs at the DFT level are sensitive to the choice of functional and atomic asymptote. Sixteen functionals predicted the BDE within 20 kJ mol-1 of the FPD value.

Next-Generation 3,3'-AlkoxyBTPs as Complexants for Minor Actinide Separation from Lanthanides: A Comprehensive Separations, Spectroscopic, and DFT Study.

Progress toward the closure of the nuclear fuel cycle can be achieved if satisfactory separation strategies for the chemoselective speciation of the trivalent actinides from the lanthanides are realized in a nonproliferative manner. Since Kolarik's initial report on the utility of bis-1,2,4-triazinyl-2,6-pyridines (BTPs) in 1999, a perfect complexant-based, liquid-liquid separation system has yet to be realized. In this report, a comprehensive performance assessment for the separation of 241Am3+ from 154Eu3+ as a model system for spent nuclear fuel using hydrocarbon-actuated alkoxy-BTP complexants is described. These newly discovered complexants realize gains that contemporary aryl-substituted BTPs have yet to achieve, specifically: long-term stability in highly concentrated nitric acid solutions relevant to the low pH of unprocessed spent nuclear fuel, high DAm over DEu in the economical, nonpolar diluent Exxal-8, and the demonstrated capacity to complete the separation cycle with high efficiency by depositing the chelated An3+ to the aqueous layer via decomplexation of the metal-ligand complex. These soft-N-donor BTPs are hypothesized to function as bipolar complexants, effectively traversing the organic/aqueous interface for effective chelation and bound metal/ligand complex solubility. Complexant design, separation assays, spectroscopic analysis, single-crystal X-ray crystallographic data, and DFT calculations are reported.

Binding of SO3 to Group 4 Transition Metal Oxide Nanoclusters.

Transition metal oxide (TMO) clusters are being studied for their ability to absorb acid gases generated by energy production processes. The interaction of SO3, a byproduct of common industrial processes, with group 4 metal (Ti, Zr, and Hf) oxide nanoclusters, has been predicted using electronic structure methods. The calculations were done at the density functional theory (DFT) and correlated molecular orbital coupled cluster singles and doubles CCSD(T) theory levels. There is a reasonable agreement between the DFT/ωB97x-D energies with the CCSD(T) results. SO3 is predicted to strongly chemisorb to these clusters, as do NO2 and CO2. For SO3, these chemisorption processes favor binding to TMO clusters as SO42- sulfate in both the terminal and bridging configurations. It is predicted that SO3 fully extracts the bridging oxygen from the TMO lattice to form bridging SO42-. This is favorable because of the lower S-O bond dissociation energy of SO3, whereas other acid gases add across the bridging oxygen because of their higher A-O bond dissociation energy. SO3 is capable of physisorption as long as an exposed metal center is present in the lattice. If a metal center has a terminal oxo-group, then SO3 will prefer the SO42- configuration. An approximately linear relationship exists between the physisorption energy and proton affinity for rows 2 and 3 elements.