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Comprehensive Summary: We reported the synthesis, single crystal structure, and solid‐state UV‐Vis‐NIR spectroscopy of a new transplutonium metal‐organic framework (MOFs), Am(H2O)[PO[(C6H4)COO]3], denoted as AmTPO (TPO = tris(4‐carboxylphenyl)‐phosphineoxide). AmTPO forms a three‐dimensional metal−organic framework structure with americium dimers as the secondary building unit. Clear 5f → 5f transitions attributed to trivalent americium was observed in the absorption spectrum of AmTPO ranging from 300 to 1200 nm. Notably, AmTPO can maintain the crystallinity with no observable structural degradation within several months after being synthesized, revealing a long‐term radiation resistance of this structure and the potential application of MOFs as a platform for nuclear waste disposal. [ABSTRACT FROM AUTHOR]

Main observation and conclusion: Two new uranium(VI) phosphonate compounds, namely K8[N(C2H5)4]2(UO2)17(H2O)4[CH2(PO3)2]8[CH2(PO3)(PO3H)]4‧16(H2O) (1) and [N(C2H5)4]4(H3O)2(UO2)10[CH2(PO3)2]5[CH2(PO3)(PO3H)]2‧10H2O (2), have been synthesized under mild hydro/solvothermal condition. The structural analysis of the two compounds reveals that they both contain all three typical coordination geometries of the U(VI) ions, including UO6 tetragonal, UO7 pentagonal, and UO8 hexagonal bipyramids. Moreover, compound 1 displays a temperature‐induced single crystal to single crystal phase transformation as confirmed by the Single‐crystal X‐ray diffraction data collected at different temperatures. Temperature‐dependent fluorescence spectra presented herein illustrate the perturbation of the electronic structure of uranyl centers. [ABSTRACT FROM AUTHOR]