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rare earth metals; carbides; iodides; cluster
Abstract:
The compounds Ln(14)(C-2)(3)I-20 (Ln = La, Ce) are prepared from Ln.
LnI(3), and C molar ratio (11:10:9) at 920 degrees C (Ce) and 930
degrees C (La) as pure phases, forming polygonal black crystals with a
greenish lustre which are moisture and air sensitive. They are isotypic
and crystallize in the triclinic system, PI, with lattice parameters a
= 9.761(1) angstrom, b = 11.790(1)angstrom, c = 14.055(1) angstrom,
alpha = 79.60(1)degrees, beta = 71.49(1)degrees gamma = 65.79(1)degrees
(La-14(C-2)(3)I-20) and a = 9.688(1) angstrom. b = 11.670(1) angstrom,
c = 13.932(1) angstrom, alpha = 80.16(1)degrees, beta =
71.81(1)degrees, gamma = 65.88(1)degrees (Ce-14-(C-2)(3)I-20). In the
crystal structure the Ln atoms form Ln(6) octahedra centered by
C-groups. Three octahedra are condensed to the triples
((Ln(2)Ln(2)Ln(2/2)C(2))(2)(Ln(2)Ln(4/2)C(2)). The iodine atoms
coordinate the octahedra above all free edges as in a M6X12-type
cluster. The mean C-C distance in the C-2 unit is 1.39 angstrom. HRTEM
images of crystals selected from different batches prepared at lower
temperature show clusters of different lengths besides the triple
octahedra. Ce-14(C-2)(3)I-20 is a semiconductor and has an effective
magnetic moment of 2.38 mu(B).
