Polyhedral Clathrate Hydrates. III. Structure of the Tetra n-Butyl Ammonium Benzoate Hydrate

Abstract

The compound (n-C4H9)4N·C6H5COO·39½H2O forms tetragonal crystals with four molecules in the unit cell. The water structure is a hydrogen-bonded clathrate framework, in the cavities of which are located the tetra alkyl ammonium cations. The oxygen atoms of the benzoate anions are hydrogen-bonded to the water framework and form part of the polyhedral structure. This structure contains 10 pentagonal dodecahedra, 16 tetrakaidecahedra, and four pentakaidecahedra per unit cell. The 20 larger polyhedra are occupied by the 16 alkyl and four benzyl groups with a statistical disorder over two sets of equivalent cation and anion positions. There is evidence of additional hydrogen-bonded water inside some of the dodecahedra which are distorted due to the presence of the ions. The clathrate framework is iso-structural with that of other salts in this series, which have a very similar tetragonal lattice but differ in containing five tetra n-butyl ammonium salt molecules per unit cell.