inorganic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
ISSN 0108-2701
Two new compounds, b-ScTe and
Y Au , and a reassessment of Y Au
3
2
2
Ping Chai and John D. Corbett*
Department of Chemistry, Iowa State University, Ames, IA 50010, USA
Received 27 July 2011
Accepted 2 September 2011
Online 31 October 2011
Two new compounds, ꢀ-ScTe (scandium telluride) and Y Au2
3
(triyttrium digold), have been synthesized by high-tempera-
ture solid-state techniques and their crystal structures, along
with that of Y Au (diyttrium gold), have been refined by
2
single-crystal X-ray diffraction methods. ꢀ-ScTe is a super-
structure of ScTe (NiAs-type), featuring double hexagonal
close-packed layers of Te atoms with the octahedral cavities
filled by Sc atoms. Y Au displays a U Si -type structure and is
Figure 1
a) A view of one unit cell, approximately along [001]. (b) A section of
-ScTe, approximately along [100].
(
ꢀ
3
2
3
2
built from Au -centered bitrigonal prisms and centered cubes
2
approximately along [100] is shown in Fig. 1(b), in which Te
atoms form hexagonal close-packed (hcp) layers with
ABAC . . . stacking, leaving all nominal octahedral cavities
filled by Sc atoms. Note that ScTe (NiAs-type) crystallizes in
of Y atoms. The structure of Y Au is better described as an
2
inverse PbCl -type structure rather than a Co Si-type.
2
2
Comment
˚
the same space group, P6 /mmc, with a = 4.130 (5) A and c =
3
˚
6.749 (5) A, and contains simple hcp Te atoms of ABAB . . .
Research within solid-state chemistry on ternary and polynary
compounds has attracted much attention during the past few
decades because of their interesting structures, bonding and
physical properties. Knowledge of binary compounds can
provide significant references during the exploratory synthesis
of polynary compounds, and their identification is therefore
valued. Although many binary combinations of elements are
covered by binary phase diagrams and the crystal databases,
some have been missed because of the limitations of the
earlier experiments. For instance, only two compounds, viz.
ScTe and Sc Te , were in the Sc–Te phase diagram reported in
ordering with Sc atoms occupying the octahedral cavities
(Men kov et al., 1961). Therefore, ꢀ-ScTe is a stacking variant
of ScTe, with a c axis twice as large.
Y Au crystallizes in the U Si -type structure in the space
3
2
3
2
group P4/mbm (No. 127). An approximately [001] projection
˚
along the short 3.907 (3) A c axis is shown in Fig. 2. The basic
building units are an Au -centered bitrigonal prism (BTP) of
2
2
3
1990 (Okamoto, 1990), missing several examples, Sc Te, Sc Te
and Sc Te , which were discovered later during the study of
2 8 3
9
2
ternary systems (Maggard & Corbett, 1997, 1998, 2000). We
discovered that the structure of ꢀ-ScTe was still missing, with
an inverse Li O -type structure, a double hexagonal close-
2
2
packed (dhcp) version of ScTe (NiAs-type) (Men kov et al.,
961). Y Au was missed in the investigation of the Y–Au
phase diagram (Saccone et al., 1997), whereas Y Au was
1
3
2
2
identified as Co Si-type (Yakinthos et al., 1978) from lattice
2
parameters only; no refinement of powder diffraction inten-
sities was carried out. The crystal structures of these three
phases are described here.
ꢀ-ScTe is presumably a high-temperature phase with an
inverse Li O -type structure. A view of the unit cell approxi-
mately along [001] is shown in Fig. 1(a) and a section
2
2
Figure 2
A projection of Y
3 2
Au , approximately along [001].
Acta Cryst. (2011). C67, i53–i55
doi:10.1107/S010827011103589X
# 2011 International Union of Crystallography i53
Chai, Ping
