The one-dimensional polyselenide compound CsGaSe3

Article abstract of DOI:10.1002/zaac.200390105

A new one-dimensional phase, CsGaSe₃ has been synthesized and characterized by single crystal X-ray diffraction, differential thermal analysis, and single crystal UV/Vis spectroscopy. The structure contains infinite chain anions, [GaSe(Se₂)]^- separated by Cs cations. The Ga³⁺ cation is in a distorted tetrahedral environment coordinated by each two Se^2- and Se₂^2- ions. The red crystals of CsGaSe₃ absorb visible light at energies above 2.25 eV. Differential thermal analysis revealed that the compound does not melt below 1000°C. Crystal data: CsGaSe₃, monoclinic, space group P2₁/c (No 14), a=7.727(1), b=13.014(3), c=6.705(1), β=106.39(3)°, Z=4, R1=0.0469.

Full text of DOI:10.1002/zaac.200390105

The One-dimensional Polyselenide Compound CsGaSe3
Junghwan Do and Mercouri G. Kanatzidis*
East Lansing, Michigan / USA, Michigan State University, Department of Chemistry and Center for Fundamental Materials Research
Received December 19th, 2002.
Abstract. A new one-dimensional phase, CsGaSe3 has been synthe-
sized and characterized by single crystal X-ray diffraction, differen-
tial thermal analysis, and single crystal UV/Vis spectroscopy. The
structure contains infinite chain anions, [GaSe(Se2)]Ϫ separated by
Cs cations. The Ga3ϩ cation is in a distorted tetrahedral environ-
ment coordinated by each two Se2Ϫ and Se22Ϫ ions. The red crystals
of CsGaSe3 absorb visible light at energies above 2.25 eV. Differen-
tial thermal analysis revealed that the compound does not melt
below 1000 °C. Crystal data: CsGaSe3, monoclinic, space group
P21/c (No 14), aϭ7.727(1), bϭ13.014(3), cϭ6.705(1), βϭ106.39(3)°,
Zϭ4, R1ϭ0.0469.
Keywords: Semiconductors; X-ray diffraction; Crystal structure;
Thermal analysis
Die eindimensionale Polyselenid-Verbindung CsGaSe3
Inhaltsübersicht. Eine neue eindimensionale Phase, CsGaSe3, wurde
synthetisiert und durch Einkristall-Röntgenbeugung, Differential-
thermoanalyse sowie durch Einkristall-UV/Vis-Spektroskopie cha-
rakterisiert. Die Struktur besteht aus unendlichen Anionen-Ketten,
[GaSe(Se2)]Ϫ, die durch Cs-Kationen getrennt sind. Das Ga3ϩ-Ka-
und Se22Ϫ-Ionen koordiniert. Die roten Kristalle von CsGaSe3 ab-
sorbieren im sichtbaren Licht bei Energien über 2,225 eV. Die Dif-
ferentialthermoanalyse zeigte, dass die Verbindung nicht unter
1000 °C schmilzt. Die Kristalldaten von CsGaSe3 sind: monoklin,
Raumgruppe P21/c (No 14), aϭ7,727(1), bϭ13,014(3), cϭ
tion ist in verzerrt tetraedrischer Anordnung durch je zwei Se2Ϫ
-
6,705(1) A, βϭ106,39(3)°, Zϭ4, R1ϭ0,0469.
˚
1 Introduction
necting GaQ4 tetrahedra sharing their edges, while
[Ga2S5]4Ϫ chain in Na4Ga2S5 is formed by GaS4 tetrahedra
sharing corners and edges.
In this paper, we report the polychalcogenide flux syn-
thesis and characterization of the new ternary gallium se-
lenide compound, CsGaSe3. To the best of our knowledge
this rather simple compound has not been reported. It pos-
A large number of ternary group 13 chalcogenide com-
pounds with a variety of metal cations including alkali
metals has been reported. Depending on the reaction condi-
tions and the size of cations, structures with discrete molec-
ules [1Ϫ6], chains [7Ϫ11], layers [12Ϫ15], or frameworks
[16Ϫ19] are formed. In the case of gallium, examples in-
clude discrete molecules, [GanQ2nϩ2
n ϭ 1, 2, 4, 6) in K5GaSe4 [1], A6Ga2Q6 (A ϭ Na, K, Cs;
Q ϭ S, Se, Te) [2Ϫ5], Cs8Ga4Se10 [6] and Cs10Ga6Se14 [6].
sesses
a
novel chain structure with tetrahedral
(nϩ4)Ϫ
[GaSe2(Se2)2]Ϫ anions linked to each other by sharing cor-
ners as well as linking corners (via Se-Se bonds) to form
infinite [GaSe(Se2)]Ϫ chains.
]
(Q ϭ S, Se, Te;
(nϩ4)Ϫ
The chain-shaped molecules, [GanQ2nϩ2
]
(Q ϭ S, Se,
Te; n ϭ 1, 2, 4, 6) have different lengths depending on the
number of n, and are built up of edge-sharing tetrahedral
GaQ4 units. The compounds KGaQ2 (Q ϭ S, Te) [12Ϫ13],
CsGaTe2 [14], and TlGaSe2 [15] are composed of linked ad-
amantane-like Ga4Q10 units that form [GaQ2]Ϫ layers.
LiGaS2 [16] and AGa3Q5 (A ϭ Li, Na; Q ϭ Se, Te) [17Ϫ19]
have open framework structures which consist of GaS4
tetrahedra sharing corners or edges. Also, two kinds of
chain anions are known in CsGaS2 [7], TlGaQ2 (Q ϭ Se,
Te) [8Ϫ10] and Na4Ga2S5 [11]. In CsGaS2 and TlGaQ2
(Q ϭ Se, Te), the [GaQ2]Ϫ chain is constructed by con-
2 Experimental
2.1 Reagents
The following reagents in this work were used as obtained: Ga
(shots, 99.999 %; Cerac, Milwaukee, WI), As2Se3 (99.9 %; Strem
Chemicals, Newburyport, MA), Se (99.999 %; Noranda Advanced
Materials, Quebec, Canada). N,N-dimethylformamide (Spectrum
Chemicals, ACS reagent grade); diethyl ether. The Cs2Se starting
material was prepared by a stoichiometric reaction of cesium metal
and selenium in liquid NH3. Ga2Se3 was prepared by heating a
stoichiometric ratio of the elements in an evacuated silica ampule.
The mixture was heated to 800 °C in 10 h and kept for 24 h. It was
cooled to 50 °C in 10 h. The Ga2Se3 was ground and stored in a
nitrogen filled glovebox.
* Professor Dr. Mercouri G. Kanatzidis
Department of Chemistry and Center for Fundamental Materials
Research
Michigan State University
East Lansing, Michigan 48824 / USA
Email address: kanatzid@cem.msu.edu
2.2 Synthesis of CsGaSe3
Compound CsGaSe3 was initially synthesized from a mixture of
0.344g (1.0 mmol) Cs2Se, 0.094g (0.25 mmol) Ga2Se3, 0.193g
Z. Anorg. Allg. Chem. 2003, 629, 621Ϫ624  2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim 0044Ϫ2313/03/629/621Ϫ624 $ 20.00ϩ.50/0
621

J. Do, M. G. Kanatzidis
Table 1 Crystallographic details for CsGaSe3
(0.5 mmol) As2Se3, and 0.317g (4.0 mmol) Se. The reagents were
mixed, sealed in an evacuated silica tube, and heated at 550 °C for
4 days. The tube was cooled at a rate of 5 °C/h to 250 °C followed
by rapid cooling to room temperature. The solid products were
washed with N,N-dimethylformamide (DMF) and diethyl ether.
Product isolation afforded red rod-shaped single crystals of
CsGaSe3 as a single phase. Electron microprobe analysis of the
crystals gave an average composition of Cs0.90Ga0.97Se3.00. The
structural details of the compound were determined by a single-
crystal X-ray diffraction study. The product slowly decayed in air
but is stable in water and common polar solvents, such as dimethyl-
formamide (DMF) and dimethyl sulfoxide (DMSO). A reaction
without As2Se3 (Cs2Se:Ga2Se3:Se ϭ 4:1:16) also gave a single phase
of CsGaSe3. In addition a quantitative synthesis of pure CsGaSe3
was achieved by a reaction of the stoichiometric amounts of Cs2Se/
Ga2Se3/Se at 550 °C for 4 days.
formula weight
space group
439.51
P21/c (No. 14)
7.727(1)
13.014(3)
6.705(1)
106.39(3)
646.8(2)
4
˚
a, A
˚
b, A
˚
c, A
β, deg
3
˚
V, A
Z
T, K
293(2) K
0.71073
4.513
˚
λ, A
ρcalcd, g/cm3
µ, cmϪ1
265.35
F(000)
752
9184
1496
0.30 x 0.12 x 0.10
2.75Ϫ27.91
1.058
Measured reflections
Independent reflections
crystal size, mm3
θ range, deg
2
GOF on Fo
R1 [I>2σ(I)]
0.0469
0.1361
wR2a) (all data)
2.3 Characterization
a) wR2 ϭ [Σw(ΗFoΗϪΗFoΗ)2/ΣwΗFoΗ2]1/2; w ϭ 1/[σ2(Fo2) ϩ (0.084P)2 ϩ 3.04P];
P ϭ [Max(Fo2,0) ϩ 2Fc2]/3
Elemental analysis on the products was performed with a JEOL
JSM-35C scanning electron microscope (SEM) equipped with a
Tracor Northern energy dispersive spectroscopy (EDS) detector.
The sample was carbon coated and analyzed using a 20kV acceler-
ating voltage and an accumulation time of 30s.
Table 2 Atomic coordinates (x 104) and equivalent isotropic dis-
2
3
˚
placement parameters (A x 10 ) for CsGaSe3
UV/Vis optical transmission measurements were performed at
room temperature on single crystals using a Hitachi U-6000 micro-
scopic FT spectrophotometer with an Olympus BH-2 metallurgical
microscope over a range of 400-800 nm.
a)
x
y
z
Ueq
Cs
Ga
Se(1)
Se(2)
Se(3)
7458(1)
1821(1)
2930(1)
9973(1)
4491(1)
4187(1)
2720(1)
762(1)
6714(1)
1752(1)
2120(1)
1420(1)
Ϫ1543(1)
1901(1)
1380(1)
43(1)
22(1)
29(1)
28(1)
30(1)
Differential thermal analysis (DTA) was performed on Shimadzu
DTA-50 thermal analyzer. Samples (ϳ30 mg) of ground crystalline
material was sealed in a carbon coated silica ampoule under vacuum.
A similar ampoule of equal mass filled with Al2O3 was sealed and
placed on the reference side of the detector. Sample was heated to
1000 °C at 10 °C/min, isothermed for 3 min followed by cooling at
Ϫ10 °C/min to 50 °C. Residues of the DTA experiments were exam-
ined by X-ray powder diffraction. The reproducibility of the sample
was checked by running multiple heating and cooling cycles.
Raman spectra were recorded on a Holoprobe Raman spectro-
graph equipped with a CCD camera detector using 633 nm radi-
ation from a HeNe laser for excitation. Laser power at the sample
was estimated to be about 5 mW and the focused laser beam dia-
a)
U
is defined as one third of the trace of the orthogonalized Uij tensor.
eq
Table 3 Anisotropic displacement parameters (A x 103) for
2
˚
CsGaSe3
U11
U22
U33
U23
U13
U12
Cs
Ga
Se(1)
Se(2)
Se(3)
35(1)
22(1)
36(1)
27(1)
21(1)
34(1)
21(1)
19(1)
28(1)
26(1)
61(1)
24(1)
32(1)
27(1)
39(1)
Ϫ9(1)
Ϫ1(1)
1(1)
3(1)
0(1)
17(1)
6(1)
9(1)
6(1)
1(1)
1(1)
0(1)
5(1)
10(1)
3(1)
meter was ca. 10 µm. The resolution of the spectra was 4 cmϪ1
.
The anisotropic displacement factor exponent takes the form:
Ϫ2π2 [h2 a*2 U11 ϩ k2 b*2 U22 ϩ l2 c*2 U33 ϩ 2kl b*c* U23 ϩ 2hl a*b* U13 ϩ 2hk a*
b* U12
Sixty four scans were allowed to obtain good quality spectra.
]
2.4 X-ray Diffraction
Powder X-ray diffraction analyses were performed using a calib-
rated CPS 120 INEL X-ray powder diffractometer (Cu Kα radi-
ation) equipped with a position-sensitive detector, operating at
40kV/20mA with a flat sample arrangement.
The crystal structure of CsGaSe3 was determined by single-crystal
X-ray diffraction methods. Preliminary examination and data col-
lection were performed on a SMART platform diffractometer
equipped with a 1K CCD area detector using graphite monochro-
matized Mo Kα radiation at room temperature. A hemisphere of
data was collected with narrow scan widths of 0.30° in ω and an
exposure time of 30 s/frame. The data were integrated using the
SAINT program [20]. The program SADABS was used for the ab-
sorption correction [20]. The initial positions for all atoms were
obtained using direct methods and the structures were refined by
full-matrix least-squares techniques with the use of the SHELXTL
crystallographic software package [20]. The final R values are R1 ϭ
0.0469 [I > 2σ(I)] and wR2 ϭ 0.1361 [all data]. Crystallographic
details are given in Table 1. The fractional atomic coordinates,
equivalent isotropic and anisotropic displacement parameters are
given in Table 2 and 3.
3 Results and Discussion
3.1 Structure of CsGaSe3
The structure of CsGaSe3 is CsAlTe3Ϫtype [21] and is built
up of infinite 1ϱ[GaSe3]Ϫ chains separated by Csϩ cations,
Figure 1. There is one crystallographically independent gal-
lium atom in a slightly distorted tetrahedral coordination
2Ϫ
surrounded by each two Se2Ϫ and Se2 ions. The GaSe4
tetrahedra are connected to each other by sharing corners
and also by forming Se-Se bonds involving Se atoms of an-
622
Z. Anorg. Allg. Chem. 2003, 629, 621Ϫ624

The One-dimensional Polyselenide Compound CsGaSe3
Fig. 1 View of the unit cell along the c axis, 30% thermal ellipsoids.
Cesium and gallium atoms are shown as black circles. Selenium
atoms are shown as empty circles.
Fig. 3 Local environments of the Cs atom, 30 % thermal ellipsoids.
˚
Table 4 Selected bond lengths/A and angles/° for CsGaSe3
Cs-Se(1)#1
Cs-Se(2)
Cs-Se(3)
Cs-Se(2)#4
Cs-Se(1)#5
Cs-Se(2)#7
Ga-Se(2)#4
Ga-Se(1)#5
3.6858(12)
3.8436(12)
3.8602(12)
3.9500(14)
4.0676(14)
4.1104(16)
2.3834(13)
2.4179(12)
2.3712(13)
110.21(5)
109.85(4)
109.11(5)
Cs-Se(2)#2
Cs-Se(1)#3
Cs-Se(3)#1
Cs-Ga
Cs-Se(3)#6
Cs-Se(1)#8
Ga-Se(2)#2
Ga-Se(3)#9
3.7408(12)
3.8497(13)
3.9090(12)
4.0157(12)
4.0725(16)
4.2001(13)
2.4051(12)
2.4238(12)
Fig. 2 View of a [GaSe(Se2)]Ϫ chain, 30 % thermal ellipsoids.
Se(1)-Se(3)
other corner. Therefore, each gallium atom is linked by each
two Se2Ϫ and Se22Ϫ ion to form 1ϱ[GaSe(Se2)]Ϫ chains along
the c-axis, Figure 2. The Ga-Se bond lengths range from
Se(2)#4-Ga-Se(2)#2
Se(2)#2-Ga-Se(1)#5
Se(2)#2-Ga-Se(3)#9
Se(2)#4-Ga-Se(1)#5
Se(2)#4-Ga-Se(3)#9
Se(1)#5-Ga-Se(3)#9
107.15(4)
115.02(5)
105.31(5)
˚
2.383(1) to 2.424(1) A and the interchain distances are
Symmetry transformations used to generate equivalent atoms:
˚
above 3.816(2) A (Se3-Se1). The crystallographically unique
#1 Ϫxϩ1,yϩ1/2,Ϫzϩ1/2
#4 Ϫxϩ2,Ϫyϩ1,Ϫz
#2 Ϫxϩ2,yϪ1/2,Ϫzϩ1/2
#5 xϩ1,Ϫyϩ1/2,zϩ1/2
#8 Ϫxϩ1,yϩ1/2,ϪzϪ1/2
#3 x,Ϫyϩ1/2,zϩ1/2
#6 x,Ϫyϩ1/2,zϪ1/2
#9 xϩ1,y,z
Csϩ cation is eleven-coordinate by Se atoms in the range of
#7 Ϫxϩ2,Ϫyϩ1,Ϫzϩ1
˚
3.686(1)-4.200(1) A, Figure 3.Other compounds that have
the same structure include TlBS3 [22].
chain. Recently and during the revision of this paper the
isostructural CsGaS3 was also reported. [24]
Many known A/Ga/Q (A ϭ alkali metals, Q ϭ chal-
cogen) structures are based on GaQ4 tetrahedra, which are
connected to each other sharing their corners and edges.
Unlike other known compounds the unique feature of
CsGaSe3 is the presence of diselenide groups in the struc-
ture. This is a rare example of a compound containing poly-
chalcogenide bonds in the A/Group13/Q system (A ϭ alkali
metals, Q ϭ chalcogen). Compound (Ph4P)[Ga(Se6)2] is an-
other example that contains polychalcogenide Se62Ϫ ligands
and adopts a very open framework [22]. The structure of
CsGaSe3 is closely related to CsGaS2 [7], TlGaQ2 (Q ϭ Se,
Te) [8Ϫ10] and Na4Ga2S5 [11] containing [GaQ2]Ϫ chains,
which are constructed by connecting tetrahedral GaQ4
sharing their edges. Substitution of one Se2Ϫ ion in the
3.2 Characterization of CsGaSe3
CsGaSe3 does not dissolve in polar solvents such as di-
methylformamide (DMF) and dimethyl sulfoxide (DMSO).
CsGaSe3 exhibits an optical absorption edge at 2.25 eV de-
termined by single-crystal optical transmission measure-
ments, and this energy is consistent with the red color of
the compound, Figure 4.
Preliminary differential thermal analysis showed that the
compound CsGaSe3 attacks the silica tube above ϳ700 °C.
Thus, carbon-coated silica tube was used and the experi-
ment indicated no melting below 1000 °C. Visual inspection
2Ϫ
[GaSe2]Ϫ chains for Se2 ion results in the [GaSe(Se2)]Ϫ
Z. Anorg. Allg. Chem. 2003, 629, 621Ϫ624
623

J. Do, M. G. Kanatzidis
into a fine powder and pressed into a pellet to allow better
interphase contact. The resulting pellet was sealed in an
evacuated pyrex tube, and heated at various temperature for
2 days. The X-ray powder diffraction pattern of resulting
product was identical to CsGaSe3 indicating no lithium ex-
change.
In conclusion, a rather simple one-dimensional com-
pound CsGaSe3 containing diselenide ions in A/Group13/
Q (A ϭ alkali metals; Q ϭ chalcogen) system has been syn-
thesized and fully characterized. The presence of diselenide
anions in the compound obtained from a polychalcogenide
flux suggest possible new phases formed by combinations
of various polychalcogenide anions and tetrahedral build-
ing units of gallium cations.
Note added in proof: While this manuscript was in review the re-
lated isostructural sulfur analog CsGaS3 was reported: M. S. Devi,
K. Vidyasagar, J. Chem. Soc., Dalton Trans. 2002, 4751.
Fig. 4 Optical absorption spectrum showing absorption edges at
2.25 eV. The sharp noises at high absorbance are due to the very
low transmission of light at those energies.
Acknowledgements. Financial support from the National Science
Foundation (DMR-0127644) is gratefully acknowledged.
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The Raman spectrum of CsGaSe3 shows shifts at ϳ187,
ϳ226, ϳ238, ϳ259, ϳ272 cmϪ1, Figure 5. Most probably
the absorptions at 187 and 238 cmϪ1 can be assigned to the
Cs-Se and Se-Se stretching vibrations, respectively. The
shifts at 226, 259 and 272 cmϪ1 can be assigned to the Ga-
Se vibrations because the Ga-Se vibrations of β-Ga2Se3
containing GaSe4 tetrahedra occur in the region at 220,
240, 250, 280, and 300 cmϪ1 [25].
We made efforts to prepare ion-exchanged compounds
such as LiGaSe3 using a method described earlier [26].
CsGaSe3 was mixed with LiI at a ratio of 1:30 (CsGaSe3:
LiI) in a nitrogen-filled glovebox. The mixture was ground
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624
Z. Anorg. Allg. Chem. 2003, 629, 621Ϫ624