1. Colton, E., J. Amer. Chem. Soc., 82, 1002 (1960).
2. Cline, C. F., and Sands, D. E., Nature, 185, 456 (1960).
3. Moissan, H., and Stock, A., C.R. Acad. Sci., Paris, 131, 139 (1900).
4. Zhdanov, G. S., and Sevast'yanov, N. G., C.R. Acad. Sci., U.R.S.S., 32, 432 (1941). Note that the parameter values given in this work refer to an old convention (equivalent positions : 0,0,0 ; 1/3,2/3,1/3; 2/3,1/3,2/3 instead of 0,0,0 ; 1/3,2/3,2/3; 2/3,1/3,1/3).