Yttrium complexes compounds

In [20], the composition of the citrate precursor of CoFe204 is proposed as Co3Fe604(C6H607)8-6H20, i.e., two protons are detached from each molecule of citric acid, and the complex compound could be classified as an acidic salt. Distinct signatures of complex formation are obtained by means of infrared (IR) spectroscopy and nuclear magnetic resonance (NMR) for citrate complexes of iron and yttrium, potential precursors of YFe04 and... 

Neutral lanthanide complexes are convenient models for the cationic zirconocene systems and avoid complications due to the presence of counteranions and the limited solubility of ionic compounds. Dynamic NMR studies on yttrium complexes 44-46 has allowed the determination of the alkene binding enthalpy, the activation enthalpy of alkene dissociation, and the relative rates of dissociation and alkyl site exchange (site epimerisation) (Scheme 8.20). Compared to the Zr... 

Solvent-free cyclopentadienyl rare earth dichlorides have not been prepared. Only the cyclopentadienyl lanthanide dichlorides coordinated by three tetrahydrofuran molecules of the heavier lanthanides could be isolated and some of their properties were investigated (Manastyrskyj et al., 1963 Ely and Tsutsui, 1975). The corresponding yttrium complex was mentioned in a paper by Jamerson et al. (1974), but no characterization of the compound was given. The preparation of the cyclopentadienyl rare earth dichloride complexes with 2 coordinated tetrahydrofuran Ugands of Eu, with 3 THE ligands of La and TM and with 4 THE ligands of La, Sm, Eu, Tm, and Yb was also described in the meantime (Suleimanov et al., 1982c, d). 

The isolated compounds (table 16) show identical infrared spectra with a characteristic band at 1195 cm for a methyl group attached to a rare earth metal. The single crystal X-ray analysis of the yttrium (table 18, fig. 25) and of the ytterbium derivative (table 18) show both compounds to be isostructural with an approximately tetrahedral metal environment and a R(ju-CH3)2R unit like the trimethyl aluminum dimer. The and NMR spectra of the diamagnetic yttrium complex were invariant between — 40°C and +40°C with a triplet for the bridging methyl protons due to the coupling with the two equivalent yttrium atoms (tables 17, 19). 

The yttrium complex reacts with Lewis bases, like amines, tetrahydrofurane or phosphine oxides, but less readily with soft donors like phosphines, as monitored by NMR spectra. The triplet at —0.81 ppm collapses to a doublet at lower field, but no isolation of an adduct was possible, pointing out a weaker Lewis acidity for Y" in comparison to Sc. Alkyl- or alkylchloroaluminum compounds react with dimeric dicyclopentadienyl methyl yttrium to give di-ju-alkyl- or di-ju-chloro-bridged compounds as shown in eqs. (41) and (42). The chloro- and methyl-bridged complex (eq. 43) decomposes with formation of trimethyl aluminum and dicyclopentadienyl... 

Biodegradable pol5miers can be synthesized using renewable resources by conventional methods (13). For example, yttrium complexes are suitable compounds for the S5mthesis of poly(lactide)s. 

Endohedral metal fullerenes can be detected in relatively small amounts in the mass spectra in the laser vaporization cluster beams (vide supra). However, macroscopic quantities of these compounds may be produced rather readily either by vaporization in a laser furnace apparatus or by arc-burning of a composite rod of graphite and the corresponding metal oxide. In Fig. 4.50, a mass spectrum which illustrates the formation of a series of fullerene endohedral yttrium complexes obtained by laser vaporization of a composite graphite/ Y2O3 rod at 1200 ""C is reproduced. Among these species there is also one, Y2 Cs2, which corresponds to the inclusion of a metal cluster in the fullerene ball. 

Aryloxo-NHC-containing complexes could also be produced from amido precursors where the ligands also acted as internal base as shown by the Shen group. Hence, a hydroxyaryl-imidazolium ligand reacted with [LiY N(z-Pr2) 4] and BuLi at — 78 °C to give the NHC-yttrium complex [(NHQ3Y] 21 (Scheme 6.2). " From [LiYb N(z -Pr2) 4], a bis-substituted ytterbium compound [(NHC)2Yb N(z-Pr2) ] 22 was prepared. Of note, all attempts to prepare the mono-substituted complex were unsueeessful. 

The reaction reportedly takes place without the addition of base. The corresponding yttrium complexes in which Q = CH3, C2H5, n-CsHy, and i-CjH were prepared by the same workers at a later date but it was found that the ligand binds in the neutral form (Kuma and Yamada, 1975). From the analyses and conductivity measurements it was concluded that the compounds should be formulated as [Y(LH)3Cl2]Cl. The only apparent synthetic differences were that the reaction with the lanthanides was carried out at temperatures less than 50°C in the absence of a solvent whereas the reaction with yttrium took place in refluxing ethanol. 

For organometailic compounds, the situation becomes even more complicated because the presence of elements such as platinum, iron, and copper introduces more complex isotopic patterns. In a very general sense, for inorganic chemistry, as atomic number increases, the number of isotopes occurring naturally for any one element can increase considerably. An element of small atomic number, lithium, has only two natural isotopes, but tin has ten, xenon has nine, and mercury has seven isotopes. This general phenomenon should be approached with caution because, for example, yttrium of atomic mass 89 is monoisotopic, and iridium has just two natural isotopes at masses 191 and 193. Nevertheless, the occurrence and variation in patterns of multi-isotopic elements often make their mass spectrometric identification easy, as depicted for the cases of dimethylmercury and dimethylplatinum in Figure 47.4. 

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