A new family of six thallium uranium phosphites and phosphates has been synthesized. Here there are three new thallium uranyl phosphites, Tl2[(UO2)(HPO3)(H2PO3)]21, Tl2[(UO2)2(HPO3)3]·H2O 2, and Tl6[(UO2)5(H2O)(HPO3)8]·2H2O 3, a uranyl phosphate-phosphite, Tl3[(UO2)2(H1.5PO4)(H0.5PO4)(H1.5PO3)2] 4, a mixed uranium(VI)–uranium(IV) phosphate-phosphite, Tl2[(UO2)2(UIV)(H2O)(PO4)2(HPO3)2] 5, and, finally, a thallium uranium(IV) phosphate, Tl2[UIV(PO4)2] 6, which were hydrothermally synthesized using thallium carbonate, uranyl nitrate, and H3PO3 as initial reagents. The above phases were all isolated from mixtures and were characterized by single-crystal X-ray diffraction and solid-state UV–vis–NIR spectroscopy. Compounds 1, 2, 3, and 5 are isotypic to known topologies. Herein, we investigate these six new thallium compounds and explore the effects of the thallium carbonate concentration and time on the reduction of uranium, via the phosphite ligand, within the crystalline products observed and also examine ho...