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, alpha-Th(SeO3)(2), beta-Th(SeO3)(2), Th(Se2O5)(2), and Th3O2(OH)(2)(SeO4)(3), have been obtained from mild hydrothermal or low-temperature (180-220 degrees C) flux conditions and. were subsequently structurally and -spectroscopically characterized. The crystal structures of alpha-Th(SeO3)(2) and beta-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 [Se2O8](2-) dimers. Th3O2(OH)(2)(SeO4)(3) is also a 3D framework constructed by octahedral hexathorium clusters [Th-6(mu(3)-O)(4)(mu(3)-OH)(4)](12+), which are interlinked by selenate groups SeO42-. The positions of the vibrational modes associated with both (SeO32-)-O-IV and (SeO42-)-O-VI units, respectively, were determined for four compounds, and the Raman spectra of alpha- and beta-Th(SeO3)(2) are compared and discussed in detail.