Raman and X-ray crystallographic studies of solid trimethylindium

Abstract

We have re-determined the crystal and molecular structure of trimethylindium, confirming that it adopts a tetrameric form in the crystal. Improved data at 273 K allow a better description of the intermolecular interactions, which involve the sharing of one methyl group of each molecule in forming the tetramer, which has (S₄) symmetry, and a weaker interaction through another methyl group linking the tetramers into an infinite three-dimensional network. The overall co-ordination at indium may be described as trigonal bipyramidal, with the shortest InC bonds in the equatorial plane. The Raman spectrum of the crystalline solid shows bands close to those reported for the liquid, but there are splittings for some of the e′ modes that are consistent with the loss of three-fold symmetry in each molecular unit; no clear evidence for any additional bands that might be ascribed to the intermolecular links is found. A metastable, apparently amorphous phase was prepared by rapid evaporation of the solid and condensation at –46 °C. Its Raman spectrum still shows the loss of three-fold symmetry, but is less complex than that of the crystal, suggesting that the rapidly sublimed solid lacks the clear-cut tetramers found in the crystal, but has more substantial intermolecular interactions than occur in the liquid. No evidence for any other more stable crystalline phase was found.