Density functional investigations of the properties and thermochemistry of UFn and UCln (n=1,…,6)

Abstract

The structural properties and thermochemistry of the UF n and UCl n (nϭ1,...,6) molecules have been investigated using hybrid density functional theory and a small-core ͑60 electrons͒ relativistic effective core potential for the uranium atom. For the first time Bond dissociation energies for this whole series are computed and shown to be in good agreement with experiment. The geometry and electronic structure of each molecule was characterized.

UF6 and UF4 in Liquid Ammonia: [UF7(NH3)]3− and [UF4(NH3)4]

“…The energy difference between the triplet and singlet states is only a qualitative estimate due to the neglect of spin-orbit effects in the calculations, but the magnitude of the energy gap is in agreement with previous calculations on UF 4 . [24] Considering the paramagnetism of the pastel-green powder of [UF 4 -A C H T U N G T R E N N U N G (NH 3 ) 4 ], the obtained triplet ground state is in accord with the SQUID magnetic measurements. Structure optimization of the [UF 4 A C H T U N G T R E N N U N G (NH 3 ) 4 ] molecule does not alter its basic structural motif and it retains the D 2 point-group symmetry, although the theoretical bond distances and angles do show some variation in comparison with the solid-state structure (Table 2).…”

“…The B3LYP hybrid functional combined with a small-core RECP and a good-quality valence basis set has been previously shown to describe the structural and electronic characteristics of uranium fluorides well compared with experimental determinations and higher levels of theory. [24,37,38] The structure of the [UF 4 A C H T U N G T R E N N U N G (NH 3 ) 4 ] molecule was optimized without any symmetry constraints and the optimized structure was characterized as a true local minimum by performing a harmonic frequency calculation. To cope with the anionic charge of the [UF 7 A C H T U N G T R E N N U N G (NH 3 )] 3À anion, the COSMO solvation model [39] with the approximate dielectric constant of liquid ammonia at À40 8C (e = 23) [40] was used.…”

“…[24] Isodensity plots of total spin density and the two singly occupied molecular orbitals of [UF 4 In the case of the [UF 7 A C H T U N G T R E N N U N G (NH 3 )] 3À anion, the anionic charge was countered by using the COSMO solvation model and the calculations were performed at the experimentally determined structure. Similar to the [UF 4 …”

Structure of the complex UCl4∙2DMF by vibrational infrared spectroscopy and density functional theory

“…Results of DFT-calculations performed with the all-electron basis set using different functionals for the four variants (T d , D 2d , C 3v , and C 2v ) of the uranium tetrahalide structure [23,25,30] confirmed the experimental data because the structure of symmetry T d had the lowest energy. The calculated UCl 4 bond lengths were 2.494 (BP functional), 2.526 (BLYP), 2.496 (PBE), 2.509 (RPBE) [25], 2.513 (B3LYP), and 2.494 A° (PBE0) [23].…”

“…1a) has a regular tetrahedral structure of symmetry T d . Such a representation was formulated based on numerous experimental and theoretical investigations of both UCl 4 and other uranium tetrahalides [19][20][21][22][23][24][25][26][27][28][29][30][31][32]. All four bond lengths are identical for this structure.…”