Brown crystalline tricyclopentadienyl cerium tetrahydrofuranate (THF)
complex (eta5-C5H5)3Ce(THF) was prepared by the reaction of (NH4)2Ce(N
O3)6 with sodium cyclopentadienide (C5H5Na) in THF at molar ratio of 1
:6. ErCl3.4THF reacts with potassium cyclooctadienide (C8H11K) at - 78
-degrees-C and then with C5H5Na at room temperature in THF at a molar
ratio of 1:1:2 to give pink crystals of (eta5-C5H5),Er(THF). The cryst
al structure determination of both these complexes shows that both bel
ong to monoclinic space group P2(1)/n, but their structures differ in
that the Ce complex is not isostructural with (eta'-C5H5)3Ln(THF) (Ln
= La, Pr, Nd, Gd, Dy, Y and Lu). However, the Er complex structure is
isostructural. There are two discontinuity points at Ce and Dy but no
''gadolinium break phenomenon'' in the regularity of lanthanide contra
ction.