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While extensive success has been gained in the structural chemistry of the U-Se system, the synthesis and characterization of Th-based Se structures are widely unexplored. Here, four new Th-Se compounds, α-Th(SeO3)2, β-Th(SeO3)2, Th(Se2O5)2, and Th3O2(OH)2(SeO4)3, have been obtained from mild hydrothermal or low-temperature (180-220 °C) flux conditions and were subsequently structurally and spectroscopically characterized. The crystal structures of α-Th(SeO3)2 and β-Th(SeO3)2 are based on ThO8 and SeO3 polyhedra, respectively, featuring a three-dimensional (3D) network with selenite anions filling in the Th channels along the a axis. Th(Se2O5)2 is a 3D framework composed of isolated ThO8 polyhedra interconnected by [Se2O5]2- dimers. Th3O2(OH)2(SeO4)3 is also a 3D framework constructed by octahedral hexathorium clusters [Th6(µ3-O)4(μ3-OH)4]12+, which are interlinked by selenate groups SeO42-. The positions of the vibrational modes associated with both SeIVO32- and SeVIO42- units, respectively, were determined for four compounds, and the Raman spectra of α- and β-Th(SeO3)2 are compared and discussed in detail. [ABSTRACT FROM AUTHOR]