The structure of (nhyphen;C4H9)4N+Fmdash;middot;32.8 H2O is tetragonal, of space groupP42/mwith the unithyphen;cell dimensionsa=23.52 Aring; andc=12.30 Aring;. The clathrate host structure is similar to that of thelpar;nminus;C4H9rpar;4Nplus;C6H5minus;COOminus;middot;39.5H2Oand consists of a tetragonal pseudo bodyhyphen;centered arrangement of groups of five facehyphen;sharing pentagonal dodecahedra interlinked by tetrakaidecahedra and pentakaidecahedra. Whereas in the benzoate there are four salt molecules per unit cell, in the fluoride there are five. This difference in the number of guests accommodated in essentially the same host structure is possible because the four tetrakaidecahedra occupied by the benzoate groups are available for the four alkyl groups of the additional cation. In the fluoride hydrate, four of the cations have the central N+atom at the fourfold positions (j) and that of the fifth is disordered over the twofold position (f). Thus the structure has lower symmetry than the benzoate hydrate, which isP42/mnmby reason of the disorder of the four cations over eightfold positions.The fluoride ions replace water molecules in the host lattice, with Fmdash;middot;middot;middot;O distances of 2.80 to 2.87 Aring; forming an anionic host lattice. As in the other clathrate hydrate structures of this type, some of the pentagonal dodecahedra which are distorted by the presence of the cations are occupied by a guest species presumed to be additional water molecules.
展开▼
