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A Theoretical Study of the Structure and Bonding of UOX 4 (X=F, Cl, Br, I) Molecules: The Importance of Inverse Trans Influence
Author(s) -
Kovács Attila,
Konings Rudy J. M.
Publication year - 2006
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200500324
Subject(s) - chemistry , density functional theory , crystallography , trigonal bipyramidal molecular geometry , steric effects , atom (system on chip) , molecule , molecular geometry , basis set , bond length , crystal structure , computational chemistry , stereochemistry , organic chemistry , computer science , embedded system
10.1002/cphc.200500324.abs The structural and bonding properties of the uranium( VI ) oxyhalides UOX 4 (X=F, Cl, Br, I) have been investigated by quantum chemical calculations at three different levels of theory: quasi‐relativistic density functional theory (DFT) in conjunction with a triple‐zeta all‐electron basis set, as well as MP2 and the Becke3–Perdew–Wang91 exchange‐correlation functional in conjunction with relativistic effective core potentials. The computations located four stationary points on the potential energy surface: a tetragonal pyramid with the O atom in the apical position ( C 4 v ), a trigonal bipyramid with the O atom in the equatorial position ( C 2 v ), a trigonal bipyramid with the O atom in the axial position ( C 3 v ) and a C s structure derived from C 3 v by opening the X eq UX eq angle to near 180°. The C s minimum, however, seems to be an artefact of the Becke–Perdew functional on the flat potential energy surface. In the C 3 v structure, the linear X ax UO moieties show clearly the geometrical consequences of the inverse trans influence (ITI) effect. This interaction can stabilise these sterically less favoured geometries. Two important trends are revealed by our computations: 1) UOX 4 with the small X=F prefers the C 3 v structure, whereas with increasing halogen size the sterically less crowded C 2 v structure is more important; and 2) MP2 theory accounts to a lesser extent for the ITI effect with respect to DFT, which results in different structural preferences (MP2 for C 2 v , DFT for C 3 v ) in the heavier halides. In addition, an important bonding property of the UOX 4 molecules is the clear triple‐bond character of the formally double UO bonds.