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3. Mair, G. A., Powell, H. M., and Venanzi, L. M., Proc. Chem. Soc., 170 (1961).
4. Swallow, A. G., and Truter, M. R., Proc. Roy. Soc., A, 266, 527 (1962).
5. For example. Cotton, F. A., in Modern Coordination Chemistry, edit. by Lewis, J., and Wilkins, R. G., 379 (Interscience Publishers, London, 1960).