We are interested in the structures of small molecules in the solid phase, with particular emphasis on hydrides and tetrahydroborates. Many of these compounds exhibit dramatic structural changes on moving from the gas phase to the solid. A good example is provided by dimethylgallium tetrahydroborate, (CH₃)₂GaBH₄, which exists in the gas phase as isolated molecules, but in the solid phase distinct intermolecular interactions are observed.

Structural Characterisation of Dimethylgallium Tetrahydroborate and its Adducts with Diethyl Ether and Tetrahydrofuran
Stefan Konietzny, Holger Fleischer, Simon Parsons, and Colin R. Pulham,
J. Chem. Soc., Dalton Trans., 2001, 304-308.

Since many of these compounds are liquids or gases at ambient temperatures, crystallographic studies are performed by growing crystals at low temperature directly from the liquid contained in a capillary mounted on the X-ray diffractometer.

This technique has now been augmented by the use of a computer-controlled infrared laser that moves slowly along the capillary causing localised melting and hence encouraging growth of a single crystal. This work is in collaboration with Dr Simon Parsons.

The precise location of hydrogen atoms is often important in this type of compound, but X-ray diffraction is not an ideal technique for achieving this, particularly when hydrogen atoms are bonded to heavy atoms. For this reason, we have made use of neutron diffraction techniques at the ISIS Neutron Facility, Rutherford Appleton Laboratory. A good example of such a study is presented by the tetrahydrides of germanium and tin for which the solid state structures were determined by powder neutron diffraction.

The intermolecular interactions in solid SnD4 showing deuterium atoms from neighbouring molecules located over the faces of the central tetrahedral molecule

Mail to C.R.Pulham@ed.ac.uk