Synthetic efforts utilizing Cs2CO3,
Ag, M2S3 (M = As, Sb), and S8 in
supercritical ammonia
(160 °C) have yielded four novel, one-dimensional compounds in the
Cs−Ag−M−S system.
These members were characterized by single-crystal X-ray
diffraction and diffuse reflectance
measurements.
Cs3Ag2Sb3S8
(I) crystallizes in the monoclinic space group
P21/m with lattice
parameters of a = 10.539(3) Å, b =
7.234 (3) Å, c = 12.777 (3) Å, β = 101.96 (2)°,
V = 952.7(9) Å3, z = 2, and R = 0.0377
(wR = 0.0445). The columnar framework of this
compound
consists of [SbS2]∞
- chains
and SbS4
3- tetrahedra that are
stitched together by Ag(I) ions.
When the Cs/Sb ratio is doubled, α- and
β-Cs2AgSbS4 (II and
III, respectively) are obtained.
Both phases contain identical anionic chains which pack in
different ways. Compound II
crystallizes in the monoclinic space group
P21/c with a =
6.848(3) Å, b = 11.413(3) Å, c
=
13.187(3) Å, β = 102.45(3)°, V =
1006.5(6) Å3,
z = 4, and R
= 0.0414 (wR = 0.0498).
Compound III was refined in the triclinic space group
P1̄ with a = 6.917(2) Å, b =
7.341(2)
Å, c = 10.998(2) Å, α = 73.83(2)°, β
= 76.08(2)°, γ = 71.71(2)°, V =
502.0(2) Å3, z = 2, and
R = 0.0343 (wR = 0.0423). Compound
IV, the isostructural arsenic analog of III,
Cs2AgAsS4,
has also been prepared and structured: a = 6.783(2)
Å, b = 7.191(2) Å, c = 11.088(2)
Å, α
= 73.61(3)°, β = 75.10(3)°, γ =
70.83(3)°, V = 481.9(2) Å3,
z = 2, and R = 0.0397 (wR
=
0.0601). The infinite, one-dimensional anionic chains in the
Cs2AgMS4 phases are built
from
isolated MS4
3- tetrahedra (M = As, Sb) joined
by Ag(I) ions. In all four materials the silver
atoms are tetrahedrally coordinated by sulfur atoms, and cesium(I)
cations are located in
the surrounding voids. Bond valence sums support the electron
precise counts predicted
for all three members:
Cs3
IAg2
ISb2
IIISbVS8
-II
and
Cs2
IAgIMVS4
-II.
Optical bandgaps determined via diffuse reflectance measurements indicate that these are wide
bandgap materials
(2.1−2.7eV) and thus are in agreement with the expected electronic
configurations.