Solid State Chemistry of Ten-Fold Coordinate Thorium(IV) Complexes with Oxalates in the Presence of Ammonium and Hydrazinium Ions

Double and triple thorium oxalates have been synthesized by successive evaporation of a solution of thorium nitrate, ammonium, or hydrazinium oxalate and hydrogen peroxide. Compounds M6Ca2Th2(C2O4)9­·nH2O (M = NH4 +, N2H5 +) (1) were first accidentally obtained due to the unexpected presence of calcium as impurities in the thorium nitrate used. Further evaporation led to the M2Th2(C2O4)5­·nH2O (M = NH4 +, N2H5 +) (2) precipitation. After an additional evaporation of 2 weeks, compounds (2) transform into M4Th­(C2O4)4­·nH2O (M = NH4 +, N2H5 +) (3). In the three compounds, thorium is coordinated by five bidentate oxalate ions. In (1) Th­(C2O4)5 entities share an oxalate ion to form dimeric units further connected by Ca­(C2O4)5 (M = NH4 +) or Ca­(C2O4)5­(H2O) (M = N2H5 +) entities to build three-dimensional (3D) frameworks. Compounds (2) exhibit a 3D honeycomb thorium oxalate framework. Compounds (3) contain chains of oxalate-shared Th­(C2O4)5 entities, whereas, in solution, the compound (NH4)2Th2­(C2O4)5­·1.5H2O (2) reacts with oxalate ions and turns into compound (NH4)4Th­(C2O4)4­·4H2O (3); in the solid state the chains of the compound (3) condense to form the 3D framework of the compound (2) and release solid ammonium oxalate.