Crystal Chemistry of the New Families of Interstitial
Compounds R<sub>6</sub>Mg<sub>23</sub>C (R = La, Ce, Pr, Nd, Sm, or
Gd) and Ce<sub>6</sub>Mg<sub>23</sub>Z (Z = C, Si, Ge, Sn, Pb, P,
As, or Sb)
Federico Wrubl
Pietro Manfrinetti
Marcella Pani
Pavlo Solokha
Adriana Saccone
10.1021/acs.inorgchem.5b02114.s003
https://acs.figshare.com/articles/dataset/Crystal_Chemistry_of_the_New_Families_of_Interstitial_Compounds_R_sub_6_sub_Mg_sub_23_sub_C_R_La_Ce_Pr_Nd_Sm_or_Gd_and_Ce_sub_6_sub_Mg_sub_23_sub_Z_Z_C_Si_Ge_Sn_Pb_P_As_or_Sb_/2092327
The crystal chemical features of
the new series of compounds R<sub>6</sub>Mg<sub>23</sub>C with R =
La–Sm or Gd and Ce<sub>6</sub>Mg<sub>23</sub>Z with Z = C,
Si, Ge, Sn, Pb, P, As, or Sb have been studied by means of single-crystal
and powder X-ray diffraction techniques. All phases crystallize with
the cubic Zr<sub>6</sub>Zn<sub>23</sub>Si prototype (<i>cF</i>120, space group <i>Fm</i>3̅<i>m</i>, <i>Z</i> = 4), a filled variant of the Th<sub>6</sub>Mn<sub>23</sub> structure. While no Th<sub>6</sub>Mn<sub>23</sub>-type binary rare
earth–magnesium compound is known to exist, the addition of
a third element Z (only 3 atom %), located into the octahedral cavity
of the Th<sub>6</sub>Mn<sub>23</sub> cell (Wyckoff site 4<i>a</i>), stabilizes this structural arrangement and makes possible the
formation of the ternary R<sub>6</sub>Mg<sub>23</sub>Z compounds.
The results of both structural and topological analyses as well as
of LMTO electronic structure calculations show that the interstitial
element plays a crucial role in the stability of these phases, forming
a strongly bonded [R<sub>6</sub>Z] octahedral moiety spaced by zeolite
cage-like [Mg<sub>45</sub>] clusters. Considering these two building
units, the crystal structure of these apparently complex intermetallics
can be simplified to the NaCl-type topology. Moreover, a structural
relationship between RMg<sub>3</sub> and R<sub>6</sub>Mg<sub>23</sub>C compounds has been unveiled; the latter can be described as substitutional
derivatives of the former. The geometrical distortions and the consequent
symmetry reduction that accompany this transformation are explicitly
described by means of the Bärnighausen formalism within group
theory.
2016-01-04 00:00:00
R 6Mg compounds
R 6Z octahedral moiety
LMTO
Th 6Mn cell
Interstitial Compounds R 6Mg
Zr 6Zn prototype
Th 6Mn structure
compounds R 6Mg
Ce 6Mg
ternary R 6Mg compounds
Wyckoff site 4
structure calculations show
crystal