Four 2D uranium(VI) carboxyphosphonates, (UO2)(O3PCH2CO2H) (1), (UO2)(4)(HO3PCH2CO2)(O3PCH2CO2)(2)(H2O)(4)center dot 3H(2)O (2), (UO2)(O3PCH2CO2)center dot NH4 center dot H2O (3), and (UO2)(3)(O3PCH(CH3)CO2)(2)(O3PCH(CH3)CO2H)center dot 2NH(4)center dot H2O (4) have been prepared using hydrothermal techniques. Their crystal structures have been determined by single-crystal X-ray diffraction, and structural features have been confirmed by infrared spectroscopy, 1, 2, and 3 are constructed from the UO22+ cation and phosphonoacetate, (O3PCH2CO2), molecules, whereas 4 consists of U(VI) coordinated to 2-phosphonopropionate, (O3PCH(CH3)CO2), units. The thermal and fluorescent behaviors of these materials have also been investigated. The organophosphonate linkers observed in 2 and 4 were produced via the in situ hydrolysis of trialkylphosphonate starting materials.