1. M. C. Marignac, Ann. Chim. Phys., 60, 257–307 (1860).
2. M. C. Marignac, ibid., 8, 5–44 (1866).
3. H. J. Hurst and J. C. Taylor, Acta Crystallogr., B26, 417–421 (1970).
4. G. M. Brown and L. A. Walker, ibid., 20, 220–229 (1966).
5. Yu. E. Gorbunova, V. I. Pakhomov, V. G. Kuznetzov, and E. S. Kovaleva, Proceedings of the 3rd All-Union Symposium on Chemistry of Inorgan. Fluorides [in Russian], Odessa (1972), p. 60.