| Title
| - Computational Study of Analogues of the Uranyl Ion Containing the −NUN− Unit: Density Functional Theory Calculations on UO22+, UON+, UN2, UO(NPH3)3+, U(NPH3)24+,[UCl4{NPR3}2] (R = H, Me), and [UOCl4{NP(C6H5)3}]-
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| Abstract
| - The electronic and geometric structures of the title species have been studied computationally using quasi-relativisticgradient-corrected density functional theory. The valence molecular orbital ordering of UO22+ is found to be πg< πu< σg ≪ σu (highest occupied orbital), in agreement with previous experimental conclusions. The significantenergy gap between the σg and σu orbitals is traced to the “pushing from below” mechanism: a filled−filledinteraction between the semi-core uranium 6p atomic orbitals and the σu valence level. The U−N bonding inUON+ and UN2 is significantly more covalent than the U−O bonding in UON+ and UO22+. UO(NPH3)3+ andU(NPH3)24+ are similar to UO22+, UON+, and UN2 in having two valence molecular orbitals of metal−ligand σcharacter and two of π character, although they have additional orbitals not present in the triatomic systems, andthe U−N σ levels are more stable than the U−N π orbitals. The inversion of U−N σ/π orbital ordering is tracedto significant N−P (and P−H) σ character in the U−N σ levels. The pushing from below mechanism is found todestabilize the U−N fσ molecular orbital with respect to the U−N dσ level in U(NPH3)24+. The uranium f atomicorbitals play a greater role in metal−ligand bonding in UO22+, UN2, and U(NPH3)24+ than do the d atomic orbitals,although, while the relative roles of the uranium d and f atomic orbitals are similar in UO22+ and U(NPH3)24+,the metal d atomic orbitals have a more important role in the bonding in UN2. The preferred UNP angle in[UCl4{NPR3}2] (R = H, Me) and [UOCl4{NP(C6H5)3}]- is found to be close to 180° in all cases. This preferencefor linearity decreases in the order R = Ph > R = Me > R = H and is traced to steric effects which in all casesovercome an electronic preference for bending at the nitrogen atom. Comparison of the present iminato (UNPR3)calculations with previous extended Hückel work on d block imido (MNR) systems reveals that in all cases thereis little or no preference for linearity over bending at the nitrogen when R is (a) only σ-bound to the nitrogen and(b) sterically unhindered. The U/N bond order in iminato complexes is best described as 3.
- The geometric and electronic structures of the title compounds are probed computationally using quasi-relativistic gradient-corrected density functional theory. The relationship of U(NPR3)24+ to UO22+ is discussed, and the preference for linearity at the iminato nitrogen atom in [UCl4{NPR3}2] (R = H, Me) and [UOCl4{NP(C6H5)3}]- is probed in detail.
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