Few actinide metal-organic frameworks (MOFs) have been studied compared to transition metal MOFs, for which thousands of structures have been described. Even fewer transuranic MOFs are reported. De novo synthesis entailing solvothermal treatment of Np(V) in N,N′-dimethylformamide (DMF), organic linker, and modulator results in crystallization of two Np5+ MOFs with unprecedented secondary building units (SBUs). Infinite, helical chains of neptunyl pentagonal bipyramids connect solely through actinyl-actinyl interactions (AAIs) and bridging formate molecules in NSM, giving a topology not previously observed in MOFs. Np-Oyl bond lengths of the neptunyl cation are typical of Np(V). Unusual wheel-shaped clusters of eighteen neptunyl polyhedra connected through integral AAIs are stabilized by tetratopic linkers in the structure of NNS1. This framework is of rare (4,12)-connected shp topology. One of two crystallographically-distinct neptunium atoms displays Np-Oyl bonds lengths of 1.77(3) and 1.94(2) Å that are highly atypical for Np5+ neptunyl cations. Attempts to isolate this node without the framework were unsuccessful. The neptunium-oxide wheel cluster was interrogated by Raman spectroscopy and density functional theory calculations to assign vibrational modes of the neptunyl cations.

Unique secondary building units and topologies in neptunium metal-organic frameworks

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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