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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.

The title complexes were formed by refluxing the complexes [Cp2SmO(CH2)4CH3]2 and [Cp2DyS(CH2)3CH3]2 (Cp  C5H5) in THF and studied by X-ray crystallography. The complexes are both monomers with the central metal coordinated by three Cp ring centroids and one THF molecule to form a distorted tetrahedral geometry. The Cp groups coordinate to the metal in a η5-fashion with the average SmC distance of 2.75(2) A and DyC distance of 2.70(1) A. The SmO and DyO bond lengths are 2.512(8) and 2.462(6) A, respectively. The comparison of some significant structural parameters of the title complexes with those of the known isostructural complexes Cp3Ln·THF (Ln  La, Pr, Nd, Gd and Lu) conformed to the “lanthanide contration” effect.

A new complex, Co2Cl5(py)5 was obtained by the reaction of CoCl2·6H2O with Bun4MnO4 in pyridine in the presence of benzoic acid. The structure consists of a discrete octahedral [CoIIICl2(py)4]+ cation and a tetrahedral [CoIICl3py]− anion. The compound was also characterized by elemental analyses, IR, XPS spectra and variable-temperature magnetic susceptibility measurements. The reaction conditions indicate that when the molar ratio of benzoic acid: CoCl2·6H2O is below 0.75 the title complex cannot be obtained.

The one-pot reaction of HoCl3 with C5H6 and sodium (1 : 5 : 1 molar ratio) in THF resulted in the formation of the compound η5-CpHoCl2·3THF (Cp = C5H5), which was characterized by elemental analysis, IR and MS spectra, and X-ray crystallography, showing that it is monomeric in both the vapour and solid states. The holmium atom has a distorted octahedral geometry coordinated by one Cp ring centroid, three THF molecules and two chloride atoms. The HoC(Cp) bond lengths range from 2.656(11) to 2.674(11) A and average 2.668(11) A. The three THF molecules coordinate to the holmium atom at the HoO bond distances of 2.366(6), 2.376(6) and 2.454(7) A, respectively. A comparison of some significant structural parameters along with the isostructural series CpLnCl2·3THF (Ln = Nd, Gd, Ho, Er and Yb) was made.

Single crystal of (Cp2HoCl)2 (Cp = C5H5) were grown from CH2Cl2 solution and studied by X-ray crystallography. The molecule of the title compound is a centro-symmetric dimer with two chloride atoms bridging. The holmium atom is coordinated by two Cp ring centroids and two chloride atoms to form a distorted tetrahedral geometry. The average HoCl and HoC(Cp) bond distances are 2.674(5) and 2.60(2) A, respectively. A comparison of some significant structural parameters along the structural series Cp2MCl2 (M = Sc, Ho, Er and Yb) with metal ionic radii was made. The magnetic susceptibility of the title compound has been measured in the range 74–300 K and shows linear Curie-Weiss behaviour with C - 14.3, θ = 1.2 K and μeff = 10.77 B.M. There is no evidence of any magnetic interaction between metal centres.

By the reaction of Cp3Ln (Cp = C5H5; Ln = Dy, Ho, Yb) with equimolar n-propyl alcohol in THF (tetrahydrofuran) at room temperature three new binuclear organolanthanide complexes, [CP2Ln(mu-OCH2CH2CH3)]2 (Ln = Dy, Ho, Yb), have been synthesized, as shown by X-ray single-crystal structure analysis for the complex [Cp2Yb(mu-OCH2CH2CH3)]2. All the complexes were characterized by elemental analysis, IR and MS spectra. The Yb2O2 unit is planar, and the ytterbium atom is coordinated by two Cp ring centroids and two oxygen atoms of two n-propyloxide ligands to form a distorted tetrahedral geometry. The average Yb-C (Cp) bond distance is 2.589(17) angstrom. The average Yb-O distance is 2.199(5) angstrom. The Yb-Yb separation [3.521(1) angstrom] indicates that no metal-metal interaction is present.

Eight new mixed-ligand lanthanide complexes of the general formula CpLnLL′ [Ln = Sm, Dy, Ho, Yb; Cp = C5H5; L = CF3COOO; L′ = 8-O C 6 H 3 N : CHCH : C H, OC6H4(o-NH2)] have been synthesized. All the complexes were characterized by elemental analysis, IR, XPS and MS spectra, showing that they are dimers with carboxylate ions as bridging groups, and the donor atom nitrogen in each complex coordinates with the metal. Their thermal stability has been studied and discussed. All these complexes are thermally unstable, and at moderately high temperatures they tend to disproportionate into a mixture of Cp2LnL, Cp2LnL′, LnL3 and LnL′3.

Eight new complexes of the type Cp n Ln(sal) 3- n or Cp n Ln(fur) 3- n ( n = 1, 2; Cp = C 5 H 5 , Ln = Nd, Yb; sal = o -aldehydophenolato, fur = furfuralcoholato) have been synthesized and characterized. These complexes are not very stable to heat and tend to disproportionate at moderately high temperatures. Their relative stability has been determined and discussed. The disproportionation reactions are reversible.