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Treatment of Cp 3 Ln (Ln=Pr, Nd) with an equimolar amount of the Schiff base bis(acetylacetone)ethylenediamine (H 2 acacen) half hydrate (H 2 L 1 ·1/2H 2 O) or bis(salicylidene)trimethylenediamine (H 2 saltn) half hydrate (H 2 L 2 ·1/2H 2 O) in THF affords three novel μ-hydroxo-bridged tetranuclear organolanthanide complexes [η 5 -CpLn 2 L 2 (μ-OH)] 2 · n THF, L=L 1 , n =4, Ln=Pr ( 1 ), Nd ( 2 ); L=L 2 , n =2, Ln=Nd ( 3 ). A reaction scheme was proposed in which the cyclopentadienyl lanthanide coordination motif [CpLnL] ( A ) and the hydroxyl lanthanide motif [LnL(OH)] ( B ) cross-reacted and then dimerized through the μ-hydroxo bridges to give the tetranuclear Ln complexes containing an Ln 4 O 8 skeleton with two reciprocally oriented face-sharing defect cubanes. In each monomeric species [CpLn 2 L 2 (OH)] ( C ) the Ln atoms are 8- or 9-coordinated. All complexes have been characterized by EA, IR and Mass spectroscopy.

The complex CpYCl2(THF)3 (Cp  C5H5) was obtained by reacting YCl3 with sodium and cyclopentadiene (1:1:5 molar ratio) in THF at room temperature, which has been studied by X-ray crystallography. The complex is monomeric with the ytrium atom coordinated by one Cp ring centroid, three oxygen atoms from three THF molcecules and two chloride atoms to give rise to a distorted octahedral coordination. The YC(Cp) bond lengths range from 2.59(3) to 2.73(4) A and average 2.65(3) A. The THF molecules coordinate to the yttrium atom with YO distances of 2.34(2), 2.35(2), 2.35(2) and 2.50(2) A, respectively. The YCl bond lengths are 2.630(8) and 2.625(7) A, respectively. Some significant parameters of the title complex have been compared with the corresponding values of the known isostructural organolanthanide complexes of Nd, Gd, Ho, Er and Yb.

Twelve complexes of the general formula Cp n Ln(Pyr)( 3− n )(THF) (Cp = η 5 -C 5 H 5 , Pyr = pyrrolyl = NC 4 H 4 ; Ln = Sm, Dy, Yb, Lu; n = 0, 1, 2) have been synthesized. They are classified into three types: Ln(Pyr) 3 (THF), CpLn(Pyr) 2 (THF) and CP 2 Ln(Pyr)(THF). Complexes of the Ln(Pyr) 3 (THF) type have comparatively low temperatures of decomposition, whereas the others tend to disproportionate into CP 3 Ln and Ln(Pyr) 3 at moderately high temperatures.

New types of organolanthanide complexes with three different ligands, CpLn(Cl)[OCOC 6 H 4 ( o -Z)] (Ln = Sm, Yb; Z = H, F, Br, I and OCH 3 ), were synthesized. These complexes were characterized by elemental analyses, IR, MS and XPS, showing that they are dimers containing carboxylate ions as bridging groups. It was found that the donor atoms (F, Br, I and O) in the complexes only slightly coordinate with lanthanide metal.

Reaction of NaCp′ (Cp′ = C5H4CH3) with YbCl3 and YbOCl in THF results in the formation of a new complex, Cp′3Yb4(μ-Cl)6(μ3-Cl)(μ4-O)(THF)3 (1). The X-ray crystal structure of 1 reveals an oxygen-centered tetrahedral arrangement of ytterbium atoms which has μ-Cl groups bridging each edge and a μ3-Cl ligand over the trianglar face composed of Yb atoms with Cp′ groups.

When [Yb(C3N2HMe2-3,5)(C5H4Me)](C3N2H2Me2-3,5 = 3,5-dimethylpyrazole) is recrystallized by slow diffusion of hexane into a thf solution which contains a small amount of dimethylsilicone grease, it is converted into to the unexpected complex [{Yb(η2-C3N2HMe2-3,5)(µ-η1:η2-OSiMe2C3N2HMe2-3,5)(η-C5H4Me)}2] indicating a novel Me2SiO insertion reaction.

Two series of lanthanide organometallics of the general formulae, Cp2Ln(acac) and CpLn(acac)2 (Cp = cyclopentadienyl; Ln = Nd, Sm, Gd, Dy, Er; Hacac = acetylacetone), have been synthesized and characterized. These compounds are not very stable to heat and tend to disproportionate into Cp3Ln and Ln(acac)3 at moderate temperatures. The sequence of thermal stability of the compounds of these two series has been determined and discussed in connection with the lanthanide contraction effect.

The crystal and molecular structure of Yb(C5H5)2·(CH3COCHCOCH3) has been determined by a single crystal X-ray diffraction study. The crystal is triclinic with space group P 1 , a 8.694, b 9.298, c 19.948 A, α 100.08, β 91.89, γ 102.36°, V 1475.9 A3, and Z = 4 to give ρcalc 1.81 g cm−3. The structure was solved by the heavy-atom method and refined by full-matrix least-squares procedures to an R factor of 0.028 based on 3961 independent reflections. The results showed that the crystal consists of discrete molecules of Yb(C5H5)2·(CH3COCHCOCH3) and no direct interaction exists between Yb atoms. The YbO bond distances average 2.219 A. The average YbC(η5) bond distance is 2.611 A.

Twelve compounds either of type Cp2Yb(diket) or CpYb(diket)2 (Cp = η5-C5H5, diket = β-diketonato) have been synthesized. Compounds of the former type are much more thermally stable than those of the latter. But, all twelve compounds tend to dispropportionate into Cp3Yb and Yb(diket)3 at moderately high temperatures.

Two rearrangement reactions caused by the thermal instability of samarium organometallics leading to mixtures of disproportionation products have been studied. Dicyclopentadienylsamarium acetate rearranges into triscyclopentadienylsamarium and samarium acetate, while dicyclopentadienyl samarium halides (chloride, bromide, iodide) rearranges into triscyclopentadienyl samarium and the corresponding samarium halide. Both reactions are reversible.