Deficiency and Mobility of Coordinated Water in the Crystalline Nonahydrates of Scandium(II1) and Lanthanoid(II1) Trifluoromethanesulfonates

The trivalent aqua ions form tricapped trigonal prisms (TTP) in the isomorphous series of trifluoromethanesulfonates. [ M ( H 2 0 ) n ] ( C F 3 0 3 ) 3 , M = SC, Lu, Yb. 'Tm. Er and Tb. Crystallographic refinement of occupancy factors in the P63/~ns pace group yielded the number of water molecules vary between 8 to 9 for the Sc, Lu, Yb, TIII and Er compounds, respectively, with water deficiency in the capping positions. The relatively strong hydrogen bonds stabilize the TTP cage around trivalent metal ions. TIYO oxygen atoms of each sulfonate group bridge hydrogen bonds fLom two water molecules in the TTP hydrate, and in the trigonal prism the water molecules are held together pairuise along the threefold axis. Residual electron density in the plane of the capping oxlgen atoms indicates randomly distributed vacancies in the crystal structure