↑Yttrium and all lanthanides except Ce, Pm, Eu, Tm, Yb have been observed in the oxidation state 0 in bis(1,3,5-tri-t-butylbenzene) complexes, see Cloke, F. Geoffrey N. (1993). "Zero Oxidation State Compounds of Scandium, Yttrium, and the Lanthanides". Chem. Soc. Rev. 22: 17–24. doi:10.1039/CS9932200017.
↑Gschneidner, K.A. , and Eyring, L. , Handbook on the Physics and Chemistry of Rare Earths, North Holland Publishing Co. , آمستردام، 1978.