2.2.2-Cryptand complexes of neptunium(iii) and plutonium(iii)

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Abstract

The THF-soluble [An(crypt)(OTf) ₂][OTf] complexes for An = Np and Pu were synthesized from AnI ₃(THF) ₄ starting materials based on pilot studies of the An = U system. 5f ³ U( iii), 5f ⁴ Np( iii), and 5f ⁵ Pu( iii) electron configurations are indicated by DFT analysis of their UV-visible-NIR spectra.

Abstract

New coordination environments are reported for Np( iii) and Pu( iii) based on pilot studies of U( iii) in 2.2.2-cryptand (crypt). The U( iii)-in-crypt complex, [U(crypt)I ₂][I], obtained from the reaction between UI ₃ and crypt, is treated with Me ₃SiOTf (OTf = O ₃SCF ₃) in benzene to form the [U(crypt)(OTf) ₂][OTf] complex. Similarly, the isomorphous Np( iii) and Pu( iii) complexes were obtained similarly starting from [AnI ₃(THF) ₄]. All three complexes (1-An; An = U, Np, Pu) contain an encapsulated actinide in a THF-soluble complex. Absorption spectroscopy and DFT calculations are consistent with 5f ³ U( iii), 5f ⁴ Np( iii), and 5f ⁵ Pu( iii) electron configurations.

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A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu.

Stefan Grimme, Jens Antony, Stephan Ehrlich … (2010)

The method of dispersion correction as an add-on to standard Kohn-Sham density functional theory (DFT-D) has been refined regarding higher accuracy, broader range of applicability, and less empiricism. The main new ingredients are atom-pairwise specific dispersion coefficients and cutoff radii that are both computed from first principles. The coefficients for new eighth-order dispersion terms are computed using established recursion relations. System (geometry) dependent information is used for the first time in a DFT-D type approach by employing the new concept of fractional coordination numbers (CN). They are used to interpolate between dispersion coefficients of atoms in different chemical environments. The method only requires adjustment of two global parameters for each density functional, is asymptotically exact for a gas of weakly interacting neutral atoms, and easily allows the computation of atomic forces. Three-body nonadditivity terms are considered. The method has been assessed on standard benchmark sets for inter- and intramolecular noncovalent interactions with a particular emphasis on a consistent description of light and heavy element systems. The mean absolute deviations for the S22 benchmark set of noncovalent interactions for 11 standard density functionals decrease by 15%-40% compared to the previous (already accurate) DFT-D version. Spectacular improvements are found for a tripeptide-folding model and all tested metallic systems. The rectification of the long-range behavior and the use of more accurate C(6) coefficients also lead to a much better description of large (infinite) systems as shown for graphene sheets and the adsorption of benzene on an Ag(111) surface. For graphene it is found that the inclusion of three-body terms substantially (by about 10%) weakens the interlayer binding. We propose the revised DFT-D method as a general tool for the computation of the dispersion energy in molecules and solids of any kind with DFT and related (low-cost) electronic structure methods for large systems.

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Semiempirical GGA-type density functional constructed with a long-range dispersion correction.

Stefan Grimme (2006)

A new density functional (DF) of the generalized gradient approximation (GGA) type for general chemistry applications termed B97-D is proposed. It is based on Becke's power-series ansatz from 1997 and is explicitly parameterized by including damped atom-pairwise dispersion corrections of the form C(6) x R(-6). A general computational scheme for the parameters used in this correction has been established and parameters for elements up to xenon and a scaling factor for the dispersion part for several common density functionals (BLYP, PBE, TPSS, B3LYP) are reported. The new functional is tested in comparison with other GGAs and the B3LYP hybrid functional on standard thermochemical benchmark sets, for 40 noncovalently bound complexes, including large stacked aromatic molecules and group II element clusters, and for the computation of molecular geometries. Further cross-validation tests were performed for organometallic reactions and other difficult problems for standard functionals. In summary, it is found that B97-D belongs to one of the most accurate general purpose GGAs, reaching, for example for the G97/2 set of heat of formations, a mean absolute deviation of only 3.8 kcal mol(-1). The performance for noncovalently bound systems including many pure van der Waals complexes is exceptionally good, reaching on the average CCSD(T) accuracy. The basic strategy in the development to restrict the density functional description to shorter electron correlation lengths scales and to describe situations with medium to large interatomic distances by damped C(6) x R(-6) terms seems to be very successful, as demonstrated for some notoriously difficult reactions. As an example, for the isomerization of larger branched to linear alkanes, B97-D is the only DF available that yields the right sign for the energy difference. From a practical point of view, the new functional seems to be quite robust and it is thus suggested as an efficient and accurate quantum chemical method for large systems where dispersion forces are of general importance. Copyright 2006 Wiley Periodicals, Inc.