1. (a) W.C. Zeise, Oversigt Kong. Danske Vidensk. Selskabs Forhandl. (1825/1826) 13; Pogg. Ann. Phys. 9 (1827) 632; E.O. Fischer, H. Werner, Angew. Chem. 75 (1963) 57.
2. (b) J.A. Wunderlich, D.P. Mellor, Acta Crystallogr. 7 (1954) 130; J.A. Wunderlich, D.P. Mellor, Acta Crystallogr. 8 (1955) 57; J.A.J. Jarvis, B.T. Kilbourn, P.G. Owston, Acta Crystallogr. B 26 (1970) 876; J.A.J. Jarvis, B.T. Kilbourn, P.G. Owston, Acta Crystallogr. B 27 (1971) 366; R.A. Love, T.F. Koetzle, G.J.B. Williams, L.C. Andrews, R. Bau, Inorg. Chem. 14 (1975) 2653.
3. (c) M.P. Schützenberger, Ann. Chim. (Paris) 15 (1868) 100.
4. (d) D. Belli Dell' Amico, F. Calderazzo, U. Englert, G.E. Herberich, S. Ramello, J. Chem. Soc. Dalton Trans. (1996) 4317.
5. (e) W.J. Pope, S.J. Peachey, Proc. Chem. Soc. 23 (1907) 86; W.J. Pope, S.J. Peachey, J. Chem. Soc. 95 (1909) 571; M.E. Foss, C.S. Gibson, J. Chem. Soc. (1951) 299.