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Synthesis and Structure of a Terminal Uranium Nitride Complex

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Science  10 Aug 2012:
Vol. 337, Issue 6095, pp. 717-720
DOI: 10.1126/science.1223488

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UN Coordination

Uranium is best known for its radioactivity. From the standpoint of lower-energy chemistry, uranium is also intriguing for its bonding motifs, which involve trinodal f orbitals. King et al. (p. 717, published online 28 June; see the Perspective by Sattelberger and Johnson) synthesized and isolated a molecule bearing a uranium-nitrogen triple bond. Theoretical calculations allowed the mapping of the orbital interactions, distinguishing it from similar motifs in compounds of lighter metals. The preparation required use of a rigid, bulky ligand framework to keep the reactive uranium nitride group from binding to another molecule nearby, a pathway that has plagued prior attempts to prepare this class of compounds.

Abstract

The terminal uranium nitride linkage is a fundamental target in the study of f-orbital participation in metal-ligand multiple bonding but has previously eluded characterization in an isolable molecule. Here, we report the preparation of the terminal uranium(V) nitride complex [UN(TrenTIPS)][Na(12-crown-4)2] {in which TrenTIPS = [N(CH2CH2NSiPri3)3]3– and Pri = CH(CH3)2} by reaction of the uranium(III) complex [U(TrenTIPS)] with sodium azide followed by abstraction and encapsulation of the sodium cation by the polydentate crown ether 12-crown-4. Single-crystal x-ray diffraction reveals a uranium-terminal nitride bond length of 1.825(15) angstroms (where 15 is the standard uncertainty). The structural assignment is supported by means of 15N-isotopic labeling, electronic absorption spectroscopy, magnetometry, electronic structure calculations, elemental analyses, and liberation of ammonia after treatment with water.

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