1. Bellamy, L. J. and Williams, R. L.J. Chem. Soc., 1957, 4294.
2. Brown, T. L...J. Amer. Chem. Soc., 1958,80, 3513.
3. —————..Spectrochimica Acta, 1962,18, 1615.
4. Hua-Chih Cheng and Lecomte, J.Comp. Rend., 1935,201, 199.
5. Josien, M. L. and Calas, R. ——Ibid., 1955,240, 1641.