The extended chain compounds Ln12(C2)3I17 (Ln = Pr, Nd, Gd, Dy):: Synthesis, structure and physical properties

The title compounds are obtained in high yield from stoichiometric mixtures of Ln, LnI(3) and graphite, heated at 900-950 degrees C in welded Ta containers. The crystal structures of new Pr and Nd phases determined by single-crystal X-ray diffraction are related to those of other Ln(12)(C-2)(3)I-17-type compounds (C 2/c, a = 19.610(1) and 19.574(4) angstrom, b = 12.406(2) and 12.393(3) angstrom, c = 19.062(5) and 19.003(5) angstrom, beta = 90.45(3)degrees and 90.41(3)degrees, for Pr-12(C-2)(3)I-17 and Nd-12(C-2)(3)I-17, respectively). All compounds contain infinite zigzag chains of C-2-centered metal atom octahedra condensed by edge-sharing into the [tcc]infinity sequence (c = cis, t = trans) and surrounded by edge-bridging iodine atoms as well as by apical iodine atoms that bridge between chains. The polycrystalline Gd-12(C-2)(3)I-17 sample exhibits semiconducting thermal behavior which is consistent with an ionic formulation (Ln(12)(3+))(C-2(6-))(3)(I-)(17)(e(-)) under the assumption that one extra electron is localized in metal-metal bonding. The magnetization measurements on Nd-12(C-2)(3)I-17, Gd-12(C-2)(3)I-17 and Dy-12(C-2)(3)I-17 indicate the coexistence of competing magnetic interactions leading to spin freezing at T-r = 5K for the Gd phase. The Nd and Dy compounds order antiferromagnetically at T-N = 25 and 29K, respectively. For Dy-12(C-2)3I(17), a metamagnetic transition is observed at a critical magnetic field H approximate to 25 kOe. (c) 2007 Elsevier Inc. All rights reserved.