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The role of the 5f orbitals in bonding, aromaticity, and reactivity of planar isocyclic and heterocyclic uranium clusters.

Authors
  • Tsipis, Athanassios C
  • Kefalidis, Christos E
  • Tsipis, Constantinos A
Type
Published Article
Journal
Journal of the American Chemical Society
Publisher
American Chemical Society
Publication Date
Jul 16, 2008
Volume
130
Issue
28
Pages
9144–9155
Identifiers
DOI: 10.1021/ja802344z
PMID: 18570422
Source
Medline
License
Unknown

Abstract

The molecular and electronic structures, stabilities, bonding features and magnetic properties of prototypical planar isocyclic cyclo-U n X n ( n = 3, 4; X = O, NH) and heterocyclic cyclo-U n (mu 2-X) n ( n = 3, 4; X = C, CH, NH) clusters as well as the [email protected][ c-U 4(mu 2-C) 4], (E = H (+), C, Si, Ge) and [email protected][ c-U 5(mu 2-C) 5] molecules including a planar tetracoordinate element E (ptE) and pentacoordinate U (ppU) at the ring centers, respectively, have been thoroughly investigated by means of electronic structure calculation methods at the DFT level. It was shown that 5f orbitals play a key role in the bonding of these f-block metal systems significantly contributing to the cyclic electron delocalization and the associated magnetic diatropic (magnetic aromaticity) response. The aromaticity of the perfectly planar cyclo-U n X n ( n = 3, 4; X = O, NH), cyclo-U n (mu 2-X) n ( n = 3, 4; X = C, CH, NH), [email protected][ c-U 4(mu 2-C) 4], (E = H (+), C, Si, Ge) and [email protected][ c-U 5(mu 2-C) 5] clusters was verified by an efficient and simple criterion in probing the aromaticity/antiaromaticity of a molecule, that of the nucleus-independent chemical shift, NICS(0), NICS(1), NICS zz (0) and the most refined NICS zz (1) index in conjunction with the NICS scan profiles. Natural bond orbital analyses provided a clear picture of the bonding pattern in the planar isocyclic and heterocyclic uranium clusters and revealed the features that stabilize the ptE's inside the six- and eight-member uranacycle rings. The ptE's benefit from a considerable electron transfer from the surrounding uranium atoms in the [email protected][ c-U 4(mu 2-C) 4], (E = H (+), C, Si, Ge) and [email protected][ c-U 5(mu 2-C) 5] clusters justifying the high occupancy of the np orbitals of the central atom E.

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