Five new chalcohalides, Ba3GaS4X (X = Cl, Br), Ba3MSe4Cl (M = Ga, In), and Ba7In 2Se6F8: Syntheses, crystal structures, and optical properties

Article abstract of DOI:10.1021/ic401820a

Five new chalcohalides, Ba₃GaS₄X (X = Cl, Br), Ba₃MSe₄Cl (M = Ga, In), and Ba₇In ₂Se₆F₈, have been synthesized by conventional high-temperature solid-state method. The

Full text of DOI:10.1021/ic401820a

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Five New Chalcohalides, Ba3GaS4X (X = Cl, Br), Ba3MSe4Cl (M = Ga, In),
and Ba7In2Se6F8: Syntheses, Crystal Structures, and Optical Properties
Kai Feng,†,‡,§ Wenlong Yin,†,‡,§ Zuohong Lin,†,‡,§ Jiyong Yao,*,†,‡ and Yicheng Wu†,‡
‡
†Center for Crystal Research and Development and Key Laboratory of Functional Crystals and Laser Technology, Technical
Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China
§University of Chinese Academy of Sciences, Beijing 100049, China
S
* Supporting Information
ABSTRACT: Five new chalcohalides, Ba3GaS4X (X = Cl, Br), Ba3MSe4Cl (M = Ga,
In), and Ba7In2Se6F8, have been synthesized by conventional high-temperature solid-
state method. These compounds crystallize in three different interesting structure
types. Ba3GaQ4X (Q = S, X = Cl, Br; Q = Se, X = Cl) contain zigzag BaX pseudolayers
and isolated GaQ4 tetrahedra, while Ba3InSe4Cl possesses one Ba−In−Se pseudolayer
and one Ba−Cl pseudolayer, which are stacked alternately along the c-direction.
Ba7In2Se6F8 is comprised of one-dimensional ∞1 [InSe3]3− chains and unique [Ba7F8]6+
chains. In all those mixed anion compounds, the halide anions are only connected to
alkaline-earth metal through strong ionic bonding, while the M (M = Ga, In) cations
are only connected to chalcogenide anions through covalent bonding. UV−vis-NIR
spectroscopy measurements indicate that Ba3GaQ4X (Q = S, X = Cl, Br; Q = Se, X =
Cl) have band gaps of 2.14, 1.80, and 2.05 eV, respectively.
element).14 For example, the LnFeOPn6,14 superconductors
consist of alternately stacked Ln2O2 layers dominated by ionic
Ln3+−O2− bonding and Fe2Pn2 layers formed by covalent Fe−
Pn bonding. The combination and interactions of these
secondary building units with different bonding nature and
INTRODUCTION
■
Mixed anions compounds have received worldwide intensive
investigation in recent years due to their unique bonding
characteristics and fascinating physical properties.1−18 For
example the LnFeOPn (Ln = rare-earth; Pn = P, As)6−11,14
oxypnictides are the first Fe-based superconductors with high
Tc and tremendous research has been carried out in increasing
the Tc or in elucidating the superconducting mechanism. The
LaCuOQ3 oxychalcogenides and the BaCuQF (Q = S, Se, Te)2
chalcohalides show very promising property as p-type trans-
parent conducting materials that have important industrial
applications. The newly discovered supramolecular pnictideha-
lide compounds, (Hg6P3)(In2Cl9) and (Hg8As4)(Bi3Cl13)16
possess chiral three dimensional (3D) frameworks, large SHG
efficiencies, and piezoelectric performance. Ag5Te2Cl15 shows
very low thermal conductivity, a desirable property for
functions bring these materials unique and fascinating proper-
ties.
In this paper, we focus on one subset of mixed anions
compounds, namely the chalcohalides. We thoroughly inves-
tigated the Ba−M−Q−X (M = Ga, In; Q = S, Se; X = F, Cl, Br)
system as it is possible to generate new compounds with
interesting structures and properties by combining the covalent
MQ4 tetrahedra, which are typical functional units for a number
of applications such as NLO property, with the strong ionic
Ba−X bonding that are helpful to achieve a large band gap, a
desired property for a number of materials such as IR NLO
materials and transparent conductors. We first discovered four
new compounds with the stoichiometry Ba3MQ4X (M = Ga, Q
= S, X = Cl, Br; M = Ga, In, Q = Se, X = Cl). Then, efforts to
synthesize fluoride analogue led to the isolation of Ba7In2Se6F8,
which has a different composition and structure from the
Ba3MQ4X compounds. These five new chalcohalides possess
three different structure types, all belonging to centrosymmetric
structure types. In this paper, we report the syntheses, crystal
structures, and optical properties of these compounds.
17
thermoelectric materials. More recently, the Tl6SeI4 chalco-
halide was found to exhibit very promising property for efficient
X-ray and γ-ray detection. It should be noted that the ionic
liquid method has been applied as an effective way to synthesize
the chalcohalide mixed anion compounds.19−22
An interesting structural feature in these mixed anion
compounds is that if different kinds of cations are involved,
the different anions will exhibit different bond propensity with
different cations. Generally, a highly electronegative element
(e.g., O, F, Cl) tends to form strong ionic bonding
(electrostatic interactions) with a highly electropositive element
(e.g., alkali metal, alkaline-earth metal, and rare-earth metals),
whereas a less electronegative element (e.g., P, As, S, Se, Te)
tends to form a stable covalent bonding with a less
electropositive element (e.g., transition metal, or p-block
Received: July 15, 2013
© XXXX American Chemical Society
A
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Table 1. Crystal Data and Structure Refinements for Ba3GaS4X (X = Cl, Br), Ba3MSe4Cl (M = Ga, In), and Ba7In2Se6F8
Ba3GaS4Cl
Ba3GaS4Br
Ba3GaSe4Cl
Ba3InSe4Cl
Ba7In2Se6F8
fw
645.43
12.264(3)
9.557(2)
8.427(2)
90
689.90
12.311(1)
9.493(2)
8.491(1)
90
833.03
12.691(3)
9.870(2)
8.716(2)
90
878.13
8.536(1)
8.536(1)
15.015(3)
90
1816.78
24.007(5)
4.3816(9)
10.902(2)
107.19(3)
C2/m
a (Å)
b (Å)
c (Å)
β (°)
space group
V (Å3)
Z
Pnma
Pnma
Pnma
I4/mcm
1093.9(3)
4
987.7(3)
4
992.3(1)
4
1091.7(4)
4
1095.5(4)
2
T (K)
λ (Å)
ρc (g/cm3)
153(2)
0.71073
4.340
153(2)
0.71073
4.618
153(2)
0.71073
5.068
153(2)
0.71073
4.452
153(2)
0.71073
5.507
μ (mm−1
)
15.533
0.0215
0.0395
19.220
0.0411
0.1130
26.625
0.0331
26.217
0.0234
24.441
a
R(F)
0.0312
b
2
RW(Fo )
0.0734
0.0612
0.0626
a
b
2
2
4
2
R(F) = ∑ ||Fo| − |Fc ||\∑| Fo| for Fo2 > 2σ(Fo ). Rw(Fo ) = {∑[w(Fo2 − Fc2)2]/∑wFo }1/2 for all data. w−1 = σ2(Fo ) + (zP)2, z = 0.0155, 0.03, 0.03,
2
and 0.0212 for Ba3GaS4Cl, Ba3GaSe4Cl, Ba3InSe4Cl and Ba7In2Se6F8, respectively, and w−1 = σ2(Fo ) + (zP)2 + 20.000P, z = 0.05 for Ba3GaS4Br,
where P = (Max(Fo , 0) + 2 Fc2)/3.
2
program Crystalclear.23 Face-indexed absorption corrections were
EXPERIMENTAL SECTION
■
performed numerically with the use of the program XPREP.24
Single-Crystal Growth. All the following reagents were obtained
The structures were solved with the direct methods program
from Sinopharm Chemical Reagent Co., Ltd. and used as obtained: Ba
SHELXS and refined with the least-squares program SHELXL of the
(99.9%), Ga (99.99%), In (99.99%), S (99.999%), Se (99.999%), BaF2
SHELXTL.PC suite of programs.24 In the situation that elements next
(99%), BaCl2 (99%), BaBr2 (99%). BaSe, BaS, Ga2S3, Ga2Se3, In2S3,
to each other in the periodic table are involved, the assignments of
and In2Se3 were synthesized by high-temperature reaction of elements
in sealed silica tubes evacuated to 10−3 Pa.
A mixture of BaQ, M2Q3, and BaX2 in the molar ratio of 2:1:2 was
atoms are based on the bonding characteristics and bond valence
sums25 calculations. Considering the bonding characteristics in mixed
anion/mixed cation compounds, in Ba3GaS4Cl, all anions connected to
the Ga atoms are assigned as S atoms and the one connected to Ba
only is assigned as Cl atoms. The calculated bond valence sums25 is
0.97 for the Cl atom in Ba3GaS4Cl, which further proves the validity of
the atoms assignments. The final refinement included anisotropic
displacement parameters and a secondary extinction correction.
Additional experimental details are given in Table 1 and selected
metrical data are given in Tables 2, 3, and 4. Further information may
be found in Supporting Information.
Diffuse Reflectance Spectroscopy. A Cary 5000 UV−vis−NIR
spectrophotometer with a diffuse reflectance accessory was used to
measure the spectrum of Ba3GaQ4X (Q = S, X = Cl, Br; Q = Se, X =
Cl) in the range of 200 nm (6.2 eV) to 1500 nm (0.83 eV).
ground and loaded into fused silica tubes under an Ar atmosphere in a
glovebox, which was sealed under 10−3 Pa atmosphere, and then
placed in a computer-controlled furnace. The sample were heated to
1123 K in 20 h and kept at that temperature for 48 h, then cooled at a
slow rate of 4 K/h to 673 K, and finally cooled to room temperature.
The produced crystals were manually selected for structure character-
ization. All the yields based on BaQ are about 20%. Analyses of the
crystals with an EDX-equipped Hitachi S-4800 SEM showed the
presence of Ba−Ga/In−S/Se−Cl/Br in the approximate molar ratio of
31:10:47:12 and Ba−In−Se−F in the approximate molar ratio of
30:9:25:36. The color of Ba3GaS4Cl, Ba3GaS4Br, and Ba3GaSe4Cl are
orange, dark red, and red, respectively.
Solid-State Synthesis. Polycrystalline samples of the three
compounds, Ba3GaQ4X (Q = S, X = Cl, Br; Q = Se, X = Cl) were
synthesized by solid-state reaction technique. A mixture of BaQ, M2Q3,
and BaX2 according to the stoichiometric ratio were ground and
loaded into fused silica tubes under an Ar atmosphere in a glovebox,
which was sealed under 10−3 Pa atmosphere and then placed in a
computer-controlled furnace. The sample was heated to 1173 K in 20
h, kept at that temperature for 48 h, and then the furnace was turned
off.
X-ray powder diffraction analyses of the powder samples were
performed at room temperature in the angular range of 2θ = 10−70°
with a scan step width of 0.05° and a fixed counting time of 0.2 s/step
using an automated Bruker D8 X-ray diffractometer equipped with a
diffracted monochromator set for Cu Kα (λ = 1.5418 Å) radiation.
Supporting Information Figure S1 shows XRD patterns of the
polycrystalline samples of Ba3GaQ4X (Q = S, X = Cl, Br; Q = Se, X =
Cl) along with the calculated ones on the basis of the single crystal
graphic data. The patterns of the samples are in good agreement with
the calculated ones. Efforts to synthesize the powder of Ba3InSe4Cl
and Ba7In2Se6F8 were unsuccessful, which indicates that they may be
kinetically stable compounds available only by the flux method.
Structure Determination. Single-crystal X-ray diffraction data
were collected with the use of graphite-monochromatized Mo Kα (λ =
0.71073 Å) at 153 K on a Rigaku AFC10 diffractometer equipped with
a Saturn CCD detector. The collection of the intensity data, cell
refinement, and data reduction were carried out with the use of the
Table 2. Selected Interatomic Distances (Å) for Ba3GaQ4X
(Q = S, X = Cl, Br; Q = Se, X = Cl)
Ba3GaS4Cl
Ba3GaS4Br
Ba3GaSe4Cl
Ba1−Q2
Ba1−Q1 × 2
Ba1−X
Ba1−Q3
Ba1−Q1 × 2
Ba2−Q3
Ba2−Q2
Ba2−Q3
Ba2−X
3.029(1)
3.042(1)
3.134(1)
3.185(1)
3.209(1)
3.235(1)
3.266(1)
3.275(1)
3.303(1)
3.306(1)
3.406(1)
3.503(1)
3.537(1)
3.612(1)
2.232(1)
2.266(1)
2.268(1)
3.030(4)
3.019(3)
3.177(2)
3.222(4)
3.172(3)
3.233(3)
3.267(3)
3.283(2)
3.337(2)
3.722(2)
3.372(1)
3.488(3)
3.352(3)
3.512(3)
2.231(3)
2.258(4)
2.276(4)
3.158(1)
3.148(1)
3.107(2)
3.277(1)
3.296(1)
3.355(1)
3.398(1)
3.389(1)
3.349(2)
3.379(1)
3.570(2)
3.614(1)
3.668(1)
3.734(1)
2.352(1)
2.377(2)
2.384(1)
Ba2−Q1
Ba2−X
Ba2−Q2
Ba2−Q1
Ba2−Q1
Ga−Q1 × 2
Ga−Q3
Ga−Q2
B
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Table 3. Selected Interatomic Distances (Å) for Ba3InSe4Cl
Ba1−Se × 2
Ba1−Cl × 2
Ba1−Se × 4
Ba2−Se × 8
In−Se × 4
3.100(1)
3.236(1)
3.435(1)
3.585(1)
2.525(1)
Table 4. Selected Interatomic Distances (Å) for Ba7In2Se6F8
Ba1−F4 × 4
Ba1−F3 × 2
Ba1−F2 × 2
Ba2−F1 × 2
Ba2−F3
2.709(2)
2.753(4)
2.833(5)
2.584(3)
2.616(5)
2.669(4)
3.399(1)
3.513(1)
3.649(2)
2.557(2)
2.623(4)
Ba3−Se3
3.437(2)
3.469(1)
3.612(1)
2.538(2)
2.579(5)
3.421(1)
3.471(1)
3.618(1)
2.512(1)
2.533(1)
2.658(1)
Ba3−Se3 × 2
Ba3−Se2 × 2
Ba4−F2 × 2
Ba4−F4
Ba2−F2
Ba4−Se1
Ba2−Se3 × 2
Ba2−Se1 × 2
Ba2−Se1
Ba3−F3 × 2
Ba3−F4
Ba4−Se2 × 2
Ba4−Se2 × 2
In−Se3
In−Se2
In−Se1 × 2
RESULTS AND DISCUSSION
Crystal Structure of Ba3GaQ4X (Q = S, X = Cl, Br; Q =
■
Se, X = Cl). The three compounds containing Ga are
isostructural and crystallize in the centrosymmetric space
group Pnma of the orthorhombic system. Only the structure
of Ba3GaS4Cl will be discussed here. The asymmetric unit
contains two crystallographically independent Ba atoms, one
independent Ga atom, three independent S atoms, and one
independent Cl atom. Ba2 and S1 atoms are at general
positions 8d, while others are all at Wyckoff sites 4c with m
symmetry. Considering no metal−metal bond and S−S bond,
the oxidation state of 2+, 3+, 2− and 1− can be attributed to
Ba, Ga, S and Cl, respectively. In addition, the structure is
26
isotypic to that of Ba3FeS5 with Ga3+ taking the Fe2+ and Cl−
Figure 1. Crystal structure of Ba3GaS4Cl viewed down [010] direction
(A), the Ba−Cl pseudolayer viewed down [101] direction (B), and
̅
taking one S2− in Ba3FeS5 simultaneously to maintain charge
balance.
coordination environments of all cations (C).
In these chalcohalides with mixed cations, the more
electronegative halide anions are only connected to the highly
electropositive alkaline-earth element through strong ionic
bonding. In Ba3GaS4Cl, the Cl atom is surrounded by five Ba
atoms to form square pyramid with Ba1 atom as apex and four
Ba2 atoms as corners of square. Ba1 atom is linked with only
one Cl atom while Ba2 atom is linked by two Cl atoms. These
quadrangular pyramids are linked via sharing corner Ba2 atoms
to form a zigzag BaCl pseudolayer, which spread along bc plane
and stacked along a-direction with Ba1 atoms locating on two
sides (Figure 1A). In the meantime, the group IIIA element
(less electropositive element) is only connected to the
chalcogen element (less electronegative element) through
stable covalent bonding. The Ga atoms in Ba3GaS4Cl are
coordinated to four S atoms to form tetrahedra, which are
isolated from each other and located between the zigzag BaCl
pseudolayers (Figure 1B).
Figure 1C illustrates the complete coordination environment
of cations. Ga atoms are tetrahedrally coordinated to four S
atoms with Ga−S distances from 2.232(1) to 2.268(1) Å,
(Table 2), which is usual in BaGa4S7 (2.228(1) to 2.338(1)
Å),27 BaGa2SiS6 (2.212(1) to 2.239(1) Å),28 and Ba2NdGaS5
(2.239(2) Å).29 The 7-fold Ba1 atom is connected with six S
atoms and one Cl atom to generate monocapped trigonal
prism, while 9-fold Ba2 atom is joined to seven S atoms and
two Cl atoms in distorted tricapped trigonal prisms geometry
with three S atoms as caps. Ba−S interatomic distances range
from 3.029(1) to 3.612(1) Å, a little longer than those of
Ba2AgInS4 (3.128(2) to 3.314(2) Å),30 Ba3PrInS6 (3.171(1) to
3.335(1) Å),29 and Ba−Cl distances change from 3.134(1) to
3.406(1) Å, a little longer than those of BaCl2 (3.159(1) to
3.197(1) Å).31
Crystal Structure of Ba3InSe4Cl. Although Ba3InSe4Cl
possesses the same stoichiometry as Ba3GaQ4X (Q = S, X = Cl,
Br; Q = Se, X = Cl), it has a different structure type in the
centrosymmetric tetragonal space group I4/mcm. There are two
crystallographically independent Ba atoms, one independent In
atom, one independent Se atom, and one independent Cl atom
in the asymmetric unit. Ba1, Ba2, In, Se, and Cl atoms are at
Wyckoff sites 8h, 4a, 4b, 16l, and 4c with symmetries of m2m,
422, 42m, m and 4/m, respectively. Considering no metal−
̅
metal bond and Se−Se bond, the oxidation state of 2+, 3+, 2−
and 1− can be attributed to Ba, In, Se and Cl, respectively.
32
Moreover, the structure may be seen as the Cs3CoCl5
structure type with Ba2+ taking all the Cs+ positions, In3+ taking
the Co2+, and four S2− replacing four Cl− in Cs3CoCl5
simultaneously to achieve the balance of charge.
Again, the Cl atom is connected to Ba atom only in the
Ba3InSe4Cl compound and the group IIIA element In is only
C
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connected to Se element. As shown in Figure 2A, the structure
of Ba3InSe4Cl can be depicted as containing two kinds of
Crystal Structure of Ba7In2Se6F8. Ba7In2Se6F8 crystallizes
in a new structure type in the centrosymmetric monoclinic
space group C2/m. There are four crystallographically unique
Ba atoms, one unique In atom, three unique Se atoms, and four
F atoms in the asymmetric unit. Ba1 atom is at Wyckoff sites 2a
with 2/m symmetry, while others are all at Wyckoff sites 4i with
m symmetry. Considering no metal−metal bond and Se−Se
bond, the oxidation state of 2+, 3+, 2−, and 1− can be
attributed to Ba, In, Se and F, respectively.
As shown in Figure 3A, each crystallographically unique atom
can be viewed as stacking along a chain parallel to the b-axis. As
Figure 2. Crystal structure of Ba3InSe4Cl viewed down [100] direction
(A), the Ba1Cl pseudolayer viewed down [001] direction (B), and
coordination environments of all cations (C).
pseudolayers. The first pseudolayer contains only Ba1 and Cl
atoms. Each Cl is linked by four Ba1 atoms in a rectangular
geometry, which are joined through edge-sharing to form a
pseudolayer parallel to the ab plane (Figure 2B). On the other
hand, the Ba2 and In atoms are alternately connected via Se
atoms, forming chains along the a-direction. These chains then
extend along the b-direction, generating another kind of
pseudolayer. These two kinds of pseudolayers are stacked
along c-axis alternately to build up the structure.
The complete coordination environments of cations are
shown in Figure 2C. The In atom is connected with four Se
atoms in perfect tetrahedra geometry with In−Se interatomic
distance of 2.525(1) Å, (Table 3) a little shorter than those in
Ba4AgInSe6 (2.612(1) to 2.660(1) Å)33 and Ba2InYSe5
(2.505(1) to 2.684(1) Å).34 The 8-fold Ba1 atom is enjoined
with six Se atoms and two Cl atoms to form bicapped trigonal
prisms with two Cl atoms as caps. However, 8-fold Ba2 atom is
connected with eight Se atoms in distorted square antiprism
with torsion angle about 40° and identical Ba−Se interatomic
distances. The Ba−Se distances range from 3.100(1) to
3.585(1) Å, shorter than those in BaGa4Se7 (3.611(2) to
3.861(2) Å)35 and BaGa2GeSe6 (3.487(1) to 3.638(1) Å).28
The Ba−Cl interatomic distances is 3.236(1) Å, resembling that
of BaCl2 (3.159(1) to 3.197(1) Å).31
Figure 3. Crystal structure of Ba7In2Se6F8 viewed down [010]
direction (A), the [Ba7F8]6+ chains viewed down [101] (B), and
̅
coordination environments of all cations (C).
in the three chalcohalides discussed above, the halide anion, F−
in this case, is connected to Ba2+ cations only and the In atom is
only tetrahedrally connected to Se atoms. But unlike the GaQ4
tetrahedra in Ba3MS4X (M = Ga, X = Cl, Br; M = Ga, In, X =
Cl), which are isolated from each other, the InSe4 tetrahedra in
Ba7In2Se6F8 are joined together via corner-sharing forming one-
dimensional chains ∞1 [InSe3]3‑ along b-direction. For the Ba−F
sublattice, they form another set of complex [Ba7F8]6+ chains
along b in which the F2, F3, and F4 atoms are all tetrahedrally
coordinated to four Ba atoms, while the F1 atoms bridge two
Ba atoms (Figure 3B).
Figure 3C depicts the complete coordination environment of
the cations. The In atom is coordinated by four Se atoms to
form tetrahedra with In−Se interatomic distances from
2.512(1) to 2.658(1) Å, (Table 4) comparable to those in
D
dx.doi.org/10.1021/ic401820a | Inorg. Chem. XXXX, XXX, XXX−XXX