1. See: (a) G.R. Choppin, in: J.-C.G. Bünzli, G.R. Choppin (Eds.), Lanthanide Probes in Life, Chemical and Earth Sciences, Elsevier, Amsterdam, 1989, p. 1.
2. (b) R.A. Anwander, W.A. Herrmann, in: W.A. Herrmann (Ed.), Topics in Current Chemistry, vol. 178, Springer, Berlin, 1996, p. 1, and further references given therein.
3. A Steudel, E. Siebel, R.D. Fischer, G. Paolucci, V. Lucchini, J. Organomet. Chem. 556 (1998) 229 (and further references given therein).
4. See (a) G.N. LaMar, W. DeW. Horrocks, Jr., R.H. Holm (Eds.), NMR of Paramagnetic Molecules, Academic Press, New York, 1971.
5. (b) R.D. Fischer, in: T.J. Marks, R.D. Fischer (Eds.), Organometallics of the f-Elements, D. Reidel, Dordrecht, 1979, p. 337, and further references cited therein.