: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Searching for new chemically durable and radiation-resistant absorbent materials for actinides and their fission products generated in the nuclear fuel cycle remain highly desirable, for both waste management and contamination remediation. Here we present a rare case of 3D uranyl organic framework material built through polycatenating of three sets of graphene-like layers, which exhibits significant umbellate distortions in the uranyl equatorial planes studied thoroughly by linear transit calculations. This unique structural arrangement leads to high β and γ radiation-resistance and chemical stability in aqueous solutions within a wide pH range from 3 to 12. Being equipped with the highest surface area among all actinide compounds known to date and completely exchangeable [(CH3)2NH2]+ cations in the structure, this material is able to selectively remove cesium from aqueous solutions while retaining the polycatenated framework structure.

Umbellate distortions of the uranyl coordination environment result in a stable and porous polycatenated framework that can effectively remove cesium from aqueous solutions.

Covalency in Ln–Cl bonds of Oh-LnCl6x– (x = 3 for Ln = CeIII, NdIII, SmIII, EuIII, GdIII; x = 2 for Ln = CeIV) anions has been investigated, primarily using Cl K-edge X-ray absorption spectroscopy (XAS) and time-dependent density functional theory (TDDFT); however, Ce L3,2-edge and M5,4-edge XAS were also used to characterize CeCl6x– (x = 2, 3). The M5,4-edge XAS spectra were modeled using configuration interaction calculations. The results were evaluated as a function of (1) the lanthanide (Ln) metal identity, which was varied across the series from Ce to Gd, and (2) the Ln oxidation state (when practical, i.e., formally CeIII and CeIV). Pronounced mixing between the Cl 3p- and Ln 5d-orbitals (t2g* and eg*) was observed. Experimental results indicated that Ln 5d-orbital mixing decreased when moving across the lanthanide series. In contrast, oxidizing CeIII to CeIV had little effect on Cl 3p and Ce 5d-orbital mixing. For LnCl63– (formally LnIII), the 4f-orbitals participated only marginally in covalent bo...

Covalency in lanthanides. An X-ray absorption spectroscopy and density functional theory study of LnCl6(x-) (x = 3, 2).

The Ln3+ and Ln2+ complexes, Cp′3Ln, 1, (Cp′ = C5H4SiMe3) and [K(2.2.2-cryptand)][Cp′3Ln], 2, respectively, have been synthesized for the six lanthanides traditionally known in +2 oxidation states, i.e., Ln = Eu, Yb, Sm, Tm, Dy, and Nd, to allow direct structural and spectroscopic comparison with the recently discovered Ln2+ ions of Ln = Pr, Gd, Tb, Ho, Y, Er, and Lu in 2. 2-La and 2-Ce were also prepared to allow the first comparison of all the lanthanides in the same coordination environment in both +2 and +3 oxidation states. 2-La and 2-Ce show the same unusual structural feature of the recently discovered +2 complexes, that the Ln–(Cp′ ring centroid) distances are only about 0.03 A longer than in the +3 analogs, 1. The Eu, Yb, Sm, Tm, Dy, and Nd complexes were expected to show much larger differences, but this was observed for only four of these traditional six lanthanides. 2-Dy and 2-Nd are like the new nine ions in this tris(cyclopentadienyl) coordination geometry. A DFT-based model explains the res...

Structural, Spectroscopic, and Theoretical Comparison of Traditional vs Recently Discovered Ln2+ Ions in the [K(2.2.2-cryptand)][(C5H4SiMe3)3Ln] Complexes: The Variable Nature of Dy2+ and Nd2+

Chlorine K-edge X-ray absorption spectroscopy (XAS) and ground-state and time-dependent hybrid density functional theory (DFT) were used to probe the electronic structures of Oh-MCl62– (M = Ti, Zr, Hf, U) and C4v-UOCl5–, and to determine the relative contributions of valence 3d, 4d, 5d, 6d, and 5f orbitals in M–Cl bonding. Spectral interpretations were guided by time-dependent DFT calculated transition energies and oscillator strengths, which agree well with the experimental XAS spectra. The data provide new spectroscopic evidence for the involvement of both 5f and 6d orbitals in actinide–ligand bonding in UCl62–. For the MCl62–, where transitions into d orbitals of t2g symmetry are spectroscopically resolved for all four complexes, the experimentally determined Cl 3p character per M–Cl bond increases from 8.3(4)% (TiCl62–) to 10.3(5)% (ZrCl62–), 12(1)% (HfCl62–), and 18(1)% (UCl62–). Chlorine K-edge XAS spectra of UOCl5– provide additional insights into the transition assignments by lowering the symmetry...

Determining Relative f and d Orbital Contributions to M–Cl Covalency in MCl62– (M = Ti, Zr, Hf, U) and UOCl5– Using Cl K-Edge X-ray Absorption Spectroscopy and Time-Dependent Density Functional Theory

Reaction of (CpSiMe3)3U or (CpSiMe3)3Nd with (Cp*Al)4 or Cp*Ga (Cp* = C5Me5) afforded the isostructural complexes (CpSiMe3)3M−ECp* (M = U, E = Al (1); M = U, E = Ga (2); M = Nd, E = Al (3); M = Nd, E = Ga (4)). In the case of 1 and 2 the complexes were isolated in 39 and 90% yields, respectively, as crystalline solids and were characterized by single-crystal X-ray diffraction, variable-temperature 1H NMR spectroscopy, elemental analysis, variable-temperature magnetic susceptibility, and UV−visible−NIR spectroscopy. In the case of 3 and 4, the complexes were observed by variable-temperature 1H NMR spectroscopy but were not isolated as pure materials. Comparison of the equilibrium constants and thermodynamic parameters ΔH and ΔS obtained by 1H NMR titration methods revealed a much stronger U−Ga interaction in 2 than the Nd−Ga interaction in 4. Competition reactions between (CpSiMe3)3U and (CpSiMe3)3Nd indicate that Cp*Ga selectively binds U over Nd in a 93:7 ratio at 19 °C and 96:4 at −33 °C. For 1 and 3, c...

A comparison of 4f vs 5f metal-metal bonds in (CpSiMe3)3M-ECp* (M = Nd, U; E = Al, Ga; Cp* = C5Me5): synthesis, thermodynamics, magnetism, and electronic structure.

The reaction of UO2Cl2·3THF with the tridentate nitrogen donor ligand 2,6-bis(2-benzimidazolyl)pyridine (H2BBP) in pyridine leads to the formation of three different complexes: [(UO2)(H2BBP)Cl2] (1), [(UO)2(HBBP)(Py)Cl] (2), and [(UO2)(BBP)(Py)2] (3) after successive deprotonation of H2BBP with a strong base. Crystallographic determination of 1–3 reveals that increased charge through ligand deprotonation and displacement of chloride leads to equatorial planarity about uranyl as well as a more compact overall coordination geometry. Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectra of 1–3 at the U-4d edges have been recorded using a soft X-ray Scanning Transmission X-ray Microscope (STXM) and reveal the uranium 4d5/2 and 4d3/2 transitions at energies associated with uranium in the hexavalent oxidation state. First-principles Density Functional Theory (DFT) electronic structure calculations for the complexes have been performed to determine and validate the coordination characteristics, which corres...

Toward equatorial planarity about uranyl: synthesis and structure of tridentate nitrogen-donor {UO2}2+ complexes.

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A comparison of 4f vs 5f metal-metal bonds in (CpSiMe3)3M-ECp* (M = Nd, U; E = Al, Ga; Cp* = C5Me5): synthesis, thermodynamics, magnetism, and electronic structure.

Toward equatorial planarity about uranyl: synthesis and structure of tridentate nitrogen-donor {UO2}2+ complexes.