Ln 3 complexes

Rate Constants and Activation Parameters for DMF Exchange on [Ln(DMF)8]3+ complexes... 

Europium and ytterbium di-valence. The oxidation state II for Eu and Yb has already been considered when discussing the properties of a number of divalent metals (Ca, Sr, Ba in 5.4). This topic was put forward again here in order to give a more complete presentation of the lanthanide properties. The sum of the first three ionization enthalpies is relatively small the lanthanide metals are highly electropositive elements. They generally and easily form in solid oxides, complexes, etc., Ln+3 ions. Different ions may be formed by a few lanthanides such as Ce+4, Sm+2, Eu+2, Yb+2. According to Cotton and Wilkinson (1988) the existence of different oxidation states should be interpreted by considering the ionization... 

Li, Mg and Cl-isotope fractionations for gas-phase molecules and aqueous moleculelike complexes (using the gas-phase approximation) are calculated using ab initio vibrational modeling. The results below are calculated using Hartree-Fock quantum mechanical modeling. Model frequencies have not been normalized to spectroscopically measured frequencies, resulting in a probable overestimate of fractionation factors—compared for instance with Urey (1947). For consistency, results have been converted from the original format (ln 3) to... 

The Structure and Bonding of 4/ and 5/ Series Organometallic Compounds 3. Complexes of the Type Ln(Cp)2X... 

The nonacoordination is fairly common for the lanthanide and the actinide complexes. Two (Fig. 27) idealized geometries have been proposed 93) for nonacoordinated polyhedra (i) the monocapped square antiprism (C41,) and (ii) the s-tricapped trigonal prism (Hs ). Out of these two geometries, the symmetrically tricapped trigonal prism is more common than the monocapped square antiprism and it was not imtil early 1970 s that this C v) geometry has been positively identified in lanthanide complexes. However, Hoard et al. 209) may have observed this geometry in [Ln(EDTA) (OH2) 3] complex but were unable to recognize it. 

Scheme 12.3 Synthesis of rare-earth metal (Ln) surface complexes, that is, heterogenized Ln single-sites, on silica Do = donor ligands, L = monoanionic ligands and M = Al, Mg, Zr or Si M = Si refers to tethered surface species.

The described preparation of Inl is a modification of a 3-step literature procedure in which indium shot is hammered into indium foil and heated with iodine to form Inig/ The Inlg is then heated with excess indium foil to form 10314 (3 complex of Inl[lnl3]).ln a third step, the Iri2l4 is treated with diethyl ether whereupon it disproportionates to insoluble Inl and soluble Inij etherate that are separated by filtration. 

The most important result of the structure studies was undoubtedly the establishment of the fact that the crystalline isopropoxides of all rare earths are not the homoleptic Ln(OPr )3 complexes but oxoalkoxides of Ln50(0Pri)13 composition, where Ln = Sc, Y, Er, Yb (see also Fig. 4.9 a). They appear to be desolvation products of the very unstable [Ln(OPri)3( PrOH)]2 solvates (perfectly soluble and rather reactive) the complex of such composition has been isolated and characterized only for neodymium, but the IR spectroscopic evidence for the existence of such solvates was obtained also for Pr and Er. Desolvation of Ln(OBu )3 2L (Ln = Y, La L = BuOH, THF, Py) leads also to the formation of oxocomplexes the ions corresponding to the fragmentation of the homoleptic species are absent in their mass-spectra (except for [Y3(OBu,)9(tBuOH)2], where the Y3(OR)8+ ion was found along with Y30(0R)6+). The same kind transformations have been observed also for... 

In the 9-coordinate TTHA complexes of the heavier Ln3+ ions, the situation is more complex, since there also the terminal N-atom bearing the uncoordinated acetate moiety is chiral. 170 NMR [49, 50], luminescence [47, 51] and NMRD measurements [46] have shown that, for both 9- and 10-coordinate Ln(TTHA)3 complexes, the inner coordination sphere of the metal ion is fully occupied by donating groups of the ligand, leaving no space for the coordination of water. Consequently, the water proton relaxation enhancement has no inner sphere contribution and the [Gd(TTHA)]3 complex is not very suitable for application... 

The H NMR spectra of the related [La(THED)]3+ as a function of temperature reveal a dynamic process at room temperature similar to that observed for [Ln(DOTA)] complexes [143]. At ambient temperature, the 13C NMR spectra (methanol-d, ) consists of two sharp resonances assigned to the pendant arms and one broad resonance attributed to the ethylene ring carbons, which sharpens as the fast exchange limit is approached (ca. 50°C). Likewise, at -20°C the broad resonance resolves into two peaks. The increased flexibility observed for [La(THED)]3+ as compared to DOTA complexes suggests that the pendant groups contribute to the structural rigidity of the macrocyclic ring. 

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