Crystal structures of the penta- and hexa­hydrate of thulium nitrate

Tm(NO3)35H2O and Tm(NO3)36H2O, or more precisely [Tm(NO3)3(H2O)4]- H2O and m(NO3)3(H2O)4]2H2O, respectively, have been obtained from aconcentrated solution of Tm2O3 in HNO3. The crystal structures of the two hydrates show strong similarities as both crystallize in space group P1 with all atoms at general positions and contain neutral, molecular [Tm(NO3)3(H2O)4] complexes, i.e. ten-coordinated TmIII cations with three nitrate anions as bidentate ligands and four coordinating water molecules, and one or two additional crystal water molecules, respectively. All building units are connected by medium–strong to weak O—HO hydrogen bonds. Tm(NO3)36H2O represents the maximally hydrated thulium nitrate as well as the heaviest rare earth nitrate hexahydrate known to date.