title: EuTM(2)Ga(8) (TM = Co, Rh, Ir) - a contribution to the chemistry of the CeFe(2)Al(8)-type compounds.
abstract: The isostructural compounds EuTM(2)Ga(8) (TM = Co, Rh, Ir) were prepared by direct reaction of the elements by high-frequency thermal treatment. All three phases are isotypic with CeFe(2)Al(8) (space group Pbam, Pearson symbol oP44, Z = 4). The crystal structure was established from single-crystal X-ray diffraction data: a = 12.4322(7) A, b = 14.3814(9) A, and c = 4.0378(2) A for EuCo(2)Ga(8); a = 12.6001(6) A, b = 14.6757(7) A, and c = 4.1172(2) A for EuRh(2)Ga(8); and a = 12.6237(7) A, b = 14.6978(8) A, and c = 4.1486(2) A for EuIr(2)Ga(8), respectively. Analysis of the chemical bonding in EuRh(2)Ga(8) with the electron localizability tools reveals formation of the 3D [Rh(2)Ga(8)] polyanion build by polar covalent bonds. Europium interacts in two ways with the polyanion: mainly as a cation by charge transfer and additionally covalently by means of the electrons of the inner shells. Magnetic susceptibility measurements show Curie-Weiss paramagnetic behavior above 40 K with effective magnetic moments of 7.81, 8.05, and 8.27 micro(B)/f.u. for EuTM(2)Ga(8) (TM = Co, Rh, Ir). Antiferromagnetic ordering of Eu moments is observed in all three compounds below 20 K. Independently on the chemical composition of the coordination sphere, magnetic behavior and, especially, X-ray absorption spectra indicate predominantly the 4f(7) electronic configuration of europium with small admixture of the 4f(6) state.
authors.affiliation: Max-Planck-Institut für Chemische Physik fester Stoffe, Nothnitzer Str. 40, 01187 Dresden, Germany.
authors.forename: O
authors.initials: O
authors.lastname: Sichevych
authors.forename: M
authors.initials: M
authors.lastname: Kohout
authors.forename: W
authors.initials: W
authors.lastname: Schnelle
authors.forename: H
authors.initials: H
authors.lastname: Borrmann
authors.forename: R
authors.initials: R
authors.lastname: Cardoso-Gil
authors.forename: M
authors.initials: M
authors.lastname: Schmidt
authors.forename: U
authors.initials: U
authors.lastname: Burkhardt
authors.forename: Yu
authors.initials: Y
authors.lastname: Grin