Sweet, Lucas Edward (2008-12). Synthesis, structure and magnetic properties of lanthanide cluster compounds. Doctoral Dissertation. Thesis uri icon

abstract

  • This dissertation focuses on the exploratory synthesis of compounds that contain R6ZI12 (R= Ce, Gd, Er; Z=Mn, Fe, Co, C2) clusters with the goal of finding magnetically interesting compounds. Several new compounds were made via high temperature, solid state methods and structurally characterized using x-ray diffraction. Compounds that contain isolated clusters were studied in order to understand the magnetic coupling between lanthanide atoms. The exploration of transition metal centered clusters resulted in the discovery of two new structure types, CsR(R6CoI12)2 (R=Gd and Er) and (CeI)0.26(Ce6MnI9)2. The xray crystal structure of CsEr(Er6CoI12)2 was solved in the Pa3 - space group with the cell length 18.063(2) ? at 250K (Z = 4, R1 [I>2?(I)] = 0.0459). (CeI)0.26(Ce6MnI9)2 was made by combining KI, CeI3, MnI2 and Ce metal and heating to 850?C for 500 hrs. The single crystal x-ray structure for (CeI)0.26(Ce6MnI9)2 was solved in the trigonal, P3 - space group with lattice parameters of a = 11.695(1) ? c = 10.8591(2) ? (Z = 2, R1 [I>2?(I)] = 0.0895). The magnetic susceptibilities of hexanuclear gadolinium clusters in the compounds Gd(Gd6ZI12) (Z = Co, Fe or Mn), CaxGd1-x(Gd6MnI12) and CsGd(Gd6CoI12)2 are reported. The single-crystal structure of Gd(Gd6CoI12) and CaxGd1-x(Gd6MnI12) are reported here as well. The compound with a closed shell of cluster bonding electrons, Gd(Gd6CoI12), exhibits the effects of antiferromagnetic coupling over the entire range of temperatures measured (4 - 300 K). Clusters with unpaired, delocalized cluster bonding electrons (CBEs) exhibit enhanced susceptibilities consistent with strong ferromagnetic coupling, except at lower temperatures (less than 30 K) where intercluster antiferromagnetic coupling suppresses the susceptibilities. Four new compounds containing Gd6C2 clusters have been found: Gd6C2I11, Gd(Gd6C2I12), CsGd(Gd6C2I12)2 and Cs(Gd6C2I12). Gd6C2I11 and Cs(Gd6C2I12) crystallized in the P?1 space group while Gd(Gd6C2I12) and CsGd(Gd6C2I12)2 crystallized in the R?3 and Pa?3 space groups respectively. The magnetic susceptibility data for Cs(Gd6C2I12) indicate strong intracluster ferromagnetic coupling, but antiferromagnetic coupling suppresses the susceptibility below 150 K. DFT calculations on CsGd6C2I12 and molecular models indicate that the magnetic coupling between the basal Gd atoms is stronger than the magnetic coupling involving the axial Gd atoms in the distorted clusters.
  • This dissertation focuses on the exploratory synthesis of compounds that contain
    R6ZI12 (R= Ce, Gd, Er; Z=Mn, Fe, Co, C2) clusters with the goal of finding magnetically
    interesting compounds. Several new compounds were made via high temperature, solid
    state methods and structurally characterized using x-ray diffraction. Compounds that
    contain isolated clusters were studied in order to understand the magnetic coupling
    between lanthanide atoms.
    The exploration of transition metal centered clusters resulted in the discovery of
    two new structure types, CsR(R6CoI12)2 (R=Gd and Er) and (CeI)0.26(Ce6MnI9)2. The xray
    crystal structure of CsEr(Er6CoI12)2 was solved in the Pa3 - space group with the cell
    length 18.063(2) ? at 250K (Z = 4, R1 [I>2?(I)] = 0.0459). (CeI)0.26(Ce6MnI9)2 was
    made by combining KI, CeI3, MnI2 and Ce metal and heating to 850?C for 500 hrs. The
    single crystal x-ray structure for (CeI)0.26(Ce6MnI9)2 was solved in the trigonal, P3 - space
    group with lattice parameters of a = 11.695(1) ? c = 10.8591(2) ? (Z = 2, R1 [I>2?(I)] =
    0.0895).
    The magnetic susceptibilities of hexanuclear gadolinium clusters in the
    compounds Gd(Gd6ZI12) (Z = Co, Fe or Mn), CaxGd1-x(Gd6MnI12) and CsGd(Gd6CoI12)2
    are reported. The single-crystal structure of Gd(Gd6CoI12) and CaxGd1-x(Gd6MnI12) are
    reported here as well. The compound with a closed shell of cluster bonding electrons, Gd(Gd6CoI12), exhibits the effects of antiferromagnetic coupling over the entire range of
    temperatures measured (4 - 300 K). Clusters with unpaired, delocalized cluster bonding
    electrons (CBEs) exhibit enhanced susceptibilities consistent with strong ferromagnetic
    coupling, except at lower temperatures (less than 30 K) where intercluster
    antiferromagnetic coupling suppresses the susceptibilities.
    Four new compounds containing Gd6C2 clusters have been found: Gd6C2I11,
    Gd(Gd6C2I12), CsGd(Gd6C2I12)2 and Cs(Gd6C2I12). Gd6C2I11 and Cs(Gd6C2I12)
    crystallized in the P?1 space group while Gd(Gd6C2I12) and CsGd(Gd6C2I12)2 crystallized
    in the R?3 and Pa?3 space groups respectively. The magnetic susceptibility data for
    Cs(Gd6C2I12) indicate strong intracluster ferromagnetic coupling, but antiferromagnetic
    coupling suppresses the susceptibility below 150 K. DFT calculations on CsGd6C2I12
    and molecular models indicate that the magnetic coupling between the basal Gd atoms is
    stronger than the magnetic coupling involving the axial Gd atoms in the distorted
    clusters.

publication date

  • December 2008