1. Bennett, M. J., and Mason, R., Proc. Chem. Soc., 273 (1963).
2. Bennett, M. J., Gerloch, M., McCleverty, J. A., and Mason, R., Proc. Chem. Soc., 357 (1962);
3. Gerloch, M., and Mason, R., J. Chem. Soc. (in the press).
4. Wilson, F. C., and Shoemaker, D. P., J. Chem. Phys., 27, 809 (1957).
5. Berndt, A. F., and Marsh, R. E., Acta Cryst., 16, 119 (1963).