The first thorium framework compound with mixed-valent phosphorus-based (phosphite and pyrophosphate) ligands, [BMMini](2) [Ths(PO3)(4)-(H2P2O7)(3)] (ThP-1), was synthesized by ionothermal reactions concurrent with the partial oxidation of phosphoric acid. The overall structural topology of ThP-1 highly resembles that of MOF-5, containing only one type of-three-dimensional channels with a window size of 11.32 angstrom x 11.32 angstrom. ThP-1 has a free void volume of 50.8%, making it one of the most porous purely inorganic actinide-based framework materials. More importantly, ThP-1 is highly stable in aqueous solutions over an extremely wide pH range from 1 to 14 and thus may find potential applications in selective ion exchange and catalysis.