1. McClure, D.S. 1963, J. Chem.Phys. 38, p. 2289.
2. Güdel, H.U. 1977, “Colloq. Int. C.N.R.S.” No. 225, pp. 231–235.
3. Decurtins, S. and Güdel, H.U. 1982, Inorg.Chem. 21, pp. 3598 - 3606.
4. Güdel, H.U. 1983, Inorg. Chem., submitted.
5. Robbins, D.J. and Day, P. 1975, J.Phys.C: Solid State Phys. 9, pp. 867–882.