1. C.J. Ballhausen,Introduction to Ligand Field Theory (McGraw-Hill, New York, 1962).
2. H.L. Schläfer and G. Gliemann,Einführung in die Ligandenfeldtheorie (Akademische Verlagsgesellschaft, Frankfurt, 1967).
3. M. Sorai and S. Seki, J. Phys. Chem. Solids 35 (1974) 555.
4. R.H. Martin and A.H. White, Transition Metal Chemistry 4 (1968) 113.
5. P. Gütlich,Structures and Bonding, Vol. 44 (Springer-Verlag, Berlin-Heidelberg, 1981) p. 83.