case, with possible tilts and rotations of the octahedra and organic molecules. As mentioned, WO$_3$ does not form a simple cubic structure, but exhibits small distortions of bond lengths and angles which render it very slightly off-cubic, with eight formula units per cell. In extending the computations to the organic-inorganic systems then, several constraints were necessary. Firstly only one cell was used, which may affect the outcome not only due to the removal of distortion in the inorganic layer (which apparently lowers the energy in the oxide and hydrate compounds) but also because this does not allow for the differing orientation of the organic molecules in neighbouring cells. Secondly, constraints were placed on the inorganic atoms in order to maintain the position of the layer. This entailed fixing the position of the tungsten and planar oxygen atoms at the corner and edges of the cell respectively. This was sufficient to relax the atoms to a sensible structure.

These compounds are isomorphic with diaminoalkane metal halides which have been investigated by Mitzi [@4]. There, two schemes were identified for the bonding of the organic ammonium group to the inorganic layer, designated ‘bridging’ and ‘terminal’ (which we shall call ’apical’). In the 