Europium coordination number

EXAFS study on Eu2+ and Sr2+ in both solid state and aqueous solution gave coordination numbers of 8.0 for strontium(II) and 7.2 for europium(II) (228). The water exchange rate measured on the divalent europium aqua ion is the fastest ever measured by 170 NMR (Table XVI) (2). The activation volume is much more negative (—11.7 cm3 mol-1) than those determined on trivalent lanthanide aqua ions clearly indicating an a-activation mechanism which is most probably a limiting... 

A study of hydration of the complex [EuL2(H20) ](BF4)3 where L= (C N-CO-CHr OCH(Me)- 2 shows by lifetime studies of a similar sort that in aqueous acetone, x = 0.9 0.4 which gives a coordination number of nine. This complex was prepared from Eu(MeCN) (BF3)3, itself prepared from the action of NOBF4 on europium metal in acetonitrile. 

Coordination number 2 is represented by the sublimeable two coordinate bent alkyl [Yb C(SiMe3)3 2] (C-Yb-C 137°) and the europium analogue. Although there are only two Yb-C a bonds, the bending is caused by a number of agostic Yb... H-C interactions... 

The lanthanide or rare earth elements (atomic numbers 57 through 71) typically add electrons to the 4f orbitals as the atomic number increases, but lanthanum (4f°) is usually considered a lanthanide. Scandium and yttrium are also chemically similar to lanthanides. Lanthanide chemistry is typically that of + 3 cations, and as the atomic number increases, there is a decrease in radius for each lanthanide, known as the lanthanide contraction. Because bonding within the lanthanide series is usually predominantly ionic, the lanthanide contraction often determines the differences in properties of lanthanide compounds and ions. Lanthanide compounds often have high coordination numbers between 6 and 12. see also Cerium Dysprosium Erbium Europium Gadolinium Holmium Lanthanum Lutetium Praseodymium Promethium Samarium Terbium Thulium Ytterbium. 

The quantum yields for emission lines of these complexes are expected to increase as the coordination number about the rare earth becomes larger and as the energies of the ligand triplet state and ion resonance level approach one another. On the basis of these criteria, the naphthyridine complexes of Sm, Eu, Tb, and Dy might be expected to yield more intense emission spectra than similar phen and bipy complexes. Also, the number and splitting of emission lines observed for the europium complexes are indicative of the symmetry about the metal (9, 11, 15), and thus they may be used to delineate possible coordination geometries. For these reasons, we undertook an investigation of the fluorescence spectra of several naphthyridine complexes of Sm, Eu , Tb" and Dy" ... 

Hydration of lanthanide complexes. X-ray diffraction studies of the solid complexes of KLn(EDTA)(H20),c showed the number of water molecules in the coordination sphere to be three for the lighter lanthanides and two for the heavier ones for total coordination numbers of nine and eight, respectively, since EDTA is hexadentate (Hoard et al. 1967). Ots (1973) measured a maximum at europium for the heat capacity change AC° for the formation of lanthanide-EDTA complexes. This maximum was taken as a strong evidence for hydration equilibrium between the complexed species,... 

The lanthanide-nitrate interaction in anhydrous acetonitrile was investigated by means of conductimetry, vibrational spectroscopy, and luminescence measurements which are very sensitive to changes in the first solvation sphere of the metal ion (Bunzli and Choppin 1989). Conductimetiic data on 0.0001-0.01 M solutions of europium or terbium trinitrate in anhydrous acetonitrile indicate that no dissociation occurs. The vibrational spectra show the presence of coordinated acetonitrile and the nitrato group frequencies are consistent with bidentate anions of approximate C2v local symmetry (Bunzli et al. 1978). When the concentration of nitrate is increased, the formation of [R(N03) ] "b species (n>3) is clearly evidenced in the FT-IR spectra (Mabillard 1983). The coordination numbers determined for Nd, Eu, Tb and Er in solutions containing an excess of nitrate are constant (9.9 0.3) and correspond to the formation of pentanitrato [R(N03)5] species, in which the nitrate ions are bonded in a bidentate fashion and which do not contain any coordinated acetonitrile molecule. The strong nitrate/europium interaction is evidenced when water is added to acetonitrile solutions of europium trinitrate. The first two acetonitrile molecules are quantitatively replaced by water molecules, but the replacement of the remaining solvent molecules is difficult to achieve and requires... 

A large number of rare-earth adducts have been synthesized and characterized (see Gmelin Handbook of Inorganic Chemistry, Part D4, 1986 for a general review or Cunha et al. (1992) for a review on europium trigonal complexes). However, the molecular structure of only a few compounds has been established by means of single-crystal X-ray diffraction. In table 16, we compare the coordination numbers in the solid state and in solution for the solvates for which extensive data are at hand, that is, adducts with DMSO. Solid solvates R(N03)3 nDMSO display a CN change from 10 to 9 between Eu and Tb. X-ray diffraction data for 1M solutions of Er(N03)3 in DMSO yield the same coordination number (CN=9) and similar distances as in the crystalline phase (Johansson et al. 1991). 

Choppin GR, Wang ZM. Correlation between ligand coordination number and the shift of the Fq - Dq transition frequency in europium(III) complexes. Inorg Chem. 1997 36(2) 249-252. 

The tribromides of lanthanum through praseodymium possess the hexagonal UCIj-type structure (Coordination Number of lanthanide CN = 9). The tribromides of neodymium through europium possess the orthorhombic PuBr -type structure (CN = 8), while those of gadolinium through lutetium as well as those of scandium and yttrium possess the rhombohedral FeClj-type structure (CN = 6). 

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