Syntheses, crystal structures, and optical properties of K3V0.32Ta0.68S4, K6Nb1.07Ta2.93S22, K6Nb2.97Ta1.03S25, K3Cu3Nb0.98Ta1.02S8, and KCu2Nb0.53Ta0.47S4

Article abstract of DOI:10.1016/j.jssc.2007.05.015

The new compounds K₃V_0.32Ta_0.68S₄ (1), K₆Nb_1.07Ta_2.93S₂₂ (2), K₆Nb_2.97Ta_1.03S₂₅ (3), K₃Cu₃Nb_0.98Ta_1.02S₈ (4), and KCu₂Nb_0.53Ta_0.47S₄ (5) have been synthesized by the reactive flux method. Their crystal structures were determined by single crystal X-ray diffraction. Crystal data: 1: space group Pnma, a=9.2354(7), b=10.6920(6), c=9.2991(5) A, Z=4; 2: space group P2₁/c, a=7.6412(4), b=8.7572(5), c=24.5772(14) A, β=98.559(6)°, Z=2; 3: space group P2₁/n, a=15.7147(10), b=12.9840(9), c=18.2363(12) A, β=104.123(8)°, Z=4; 4: space group C2/c, a=23.5934(19), b=5.5661(2), c=14.2373(12) A, β=120.631(9)°, Z=4; 5: space group Ama2, a=7.4615(4), b=18.2902(16), c=5.5320(6) A, Z=4. The structure of compound 1 is based on discrete tetrahedral MS₄ (M=V/Ta) anions, which are separated by K⁺ cations. The structure of 2 consists of K⁺ cations and [M₄S₂₂]^6- (M=Nb/Ta) anions, in which two M₂S₁₁ building blocks are linked via terminal sulfur ligands. In 3 the complex anion [M₄S₂₅]^6- (M=Nb/Ta) is observed which comprises two M₂S₁₁ subunits bridged by a S₃ chain. In 4 ¹_∞[Cu₃M₂S₈]^3- (M=Nb/Ta) anionic chains are found which are formed by corner sharing of CuS₄ tetrahedra and edge sharing between CuS₄ and MS₄ tetrahedra. The structure of 5 consists of [Cu₂MS₄]^- (M=Nb/Ta) anionic layers separated by K⁺ cations. The CuS₄ and MS₄ tetrahedra share edges and corners yielding layers. All compounds were characterized with Raman spectroscopy and the compound 2-5 with UV/vis diffuse reflectance spectroscopy.

Full text of DOI:10.1016/j.jssc.2007.05.015

ARTICLE IN PRESS
Journal of Solid State Chemistry 180 (2007) 2166–2174
www.elsevier.com/locate/jssc
Syntheses, crystal structures, and optical properties of K V Ta S ,
3
0.32
0.68 4
K Nb Ta S , K Nb Ta S , K Cu Nb Ta S , and
1.02 8
6
1.07
2.93 22
6
2.97
1.03 25
3
3
0.98
KCu Nb Ta S
0.47 4
2
0.53
Ã
Yuandong Wu, Wolfgang Bensch
Institut f u¨ r Anorganische Chemie, Universit a¨ t Kiel, Olshausenstr. 40, D-24098 Kiel, Germany
Received 18 December 2006; received in revised form 12 March 2007; accepted 20 May 2007
Available online 26 May 2007
Abstract
The new compounds K
3 4 6 6 3 3 8 2
V0.32Ta0.68S (1), K Nb1.07Ta2.93S22 (2), K Nb2.97Ta1.03S25 (3), K Cu Nb0.98Ta1.02S (4), and KCu Nb0.53
Ta0.47S
4
(5) have been synthesized by the reactive flux method. Their crystal structures were determined by single crystal X-ray
˚
diffraction. Crystal data: 1: space group Pnma, a ¼ 9.2354(7), b ¼ 10.6920(6), c ¼ 9.2991(5) A, Z ¼ 4; 2: space group P2 /c,
1
˚
a ¼ 7.6412(4), b ¼ 8.7572(5), c ¼ 24.5772(14) A, b ¼ 98.559(6)1, Z ¼ 2; 3: space group P2
1
/n, a ¼ 15.7147(10), b ¼ 12.9840(9),
˚
˚
c ¼ 18.2363(12) A, b ¼ 104.123(8)1, Z ¼ 4; 4: space group C2/c, a ¼ 23.5934(19), b ¼ 5.5661(2), c ¼ 14.2373(12) A, b ¼ 120.631(9)1,
˚
Z ¼ 4; 5: space group Ama2, a ¼ 7.4615(4), b ¼ 18.2902(16), c ¼ 5.5320(6) A, Z ¼ 4. The structure of compound 1 is based on discrete
+
+
6ꢀ
tetrahedral MS (M ¼ V/Ta) anions, which are separated by K cations. The structure of 2 consists of K cations and [M S ]
4
4
22
6ꢀ
(
(
M ¼ Nb/Ta) anions, in which two M
2
S
11 building blocks are linked via terminal sulfur ligands. In 3 the complex anion [M
1
4
S
25
]
3ꢀ
M ¼ Nb/Ta) is observed which comprises two M
2
S
11 subunits bridged by a S
3
chain. In 4
N
[Cu
3
M
2
8
S ]
(M ¼ Nb/Ta) anionic chains
are found which are formed by corner sharing of CuS tetrahedra and edge sharing between CuS and MS tetrahedra. The structure of 5
4
4
4
ꢀ
+
consists of [Cu and MS
yielding layers. All compounds were characterized with Raman spectroscopy and the compound 2–5 with UV/vis diffuse reflectance
2
MS
4
]
(M ¼ Nb/Ta) anionic layers separated by K cations. The CuS
4
4
tetrahedra share edges and corners
spectroscopy.
r 2007 Elsevier Inc. All rights reserved.
Keywords: Molten flux method; Group 5 metal polysulfide; Crystal structure; Raman spectrum; UV/vis diffuse reflectance spectroscopy
ꢀ
1
. Introduction
units in A M S [20,22], and one-dimensional [NbS ] and
6
4
25
6
ꢀ
[TaS ] chains in NaNbS [23] and KTaS [24], respectively.
5 6 5
For the quaternary group 5 sulfides, a variety of
During the last two decades, many multinary transition
I
V
I
metal chalcogenides were synthesized by applying reactive
alkali polychalcogenide fluxes as reaction media at inter-
mediate temperature (200pTp500 1C) [1,2]. Among these
compounds ternary and quaternary sulfides of group 5
elements form a very interesting group. The structures of
compounds with composition A M M S , AM MS , and
2 4 2 4
I
3
V
2 8
I
V
A M M S (A ¼ K, Rb, Cs; M ¼ Cu, Ag; M ¼ V, Nb,
3
Ta) [3,25–36] crystallize with low-dimensional anionic
building units. The structures of these compounds can be
derived from the three dimensionally connected sulvanite-
3
4
ꢀ
group 5 ternary sulfides contain isolated tetrahedral MS
type structure Cu VS by successive substitution of the Cu
3 4
units in A MS (A ¼ Na, K, Rb, Cs; M ¼ V, Nb, Ta)
(Ag) atoms by alkali cations.
Solid solutions based on the K Nb S structure were
3
4
4
11
ꢀ
[
3–11], discrete M S groups in A M S (A ¼ K, Rb, Cs;
2
4
2
11
4
2 11
6
ꢀ
M ¼ Nb, Ta) [12–16], complex M S anions in A M S
successfully prepared via substitutions on the S atom sites
(i.e. K Nb S
Se [37], A Nb S O (A ¼ K, Rb) [38]),
4
22
A ¼ K, Rb, Cs; M ¼ Nb, Ta) [17–21], expanded M S
6
4 22
6
ꢀ
(
4
25
4
2
11ꢀx
and on the alkali atom sites (i.e. K Ba (Nb S ) [39]). But
x
4
2 10
4
2
2 11 2
Ã
there are no reports about substitutions of Nb or Ta in this
structure type. The two compounds K Nb S and
Corresponding author. Fax: +49 431 880 1520.
E-mail address: wbensch@ac.uni-kiel.de (W. Bensch).
4
2 11
0022-4596/$ - see front matter r 2007 Elsevier Inc. All rights reserved.
doi:10.1016/j.jssc.2007.05.015

ARTICLE IN PRESS
Y. Wu, W. Bensch / Journal of Solid State Chemistry 180 (2007) 2166–2174
2167
s
K Ta S are isostructural adopting the orthorhombic
4
heated at 450 1C for 6 days in a glass ampoule (Duran ).
After cooling with 2 1C/h, transparent red platelets were
obtained in a yield of about 90%. The compound is stable
in dry air for several weeks. An EDX analysis of single
crystals indicated the presence of all four elements (K, Nb,
Ta, S) in an atomic ratio of 6:1:3:22.
2 11
space group Pca2 . Therefore, it should be possible to
1
replace Nb by Ta (or vice versa) yielding the orthorhombic
structure type. Interestingly, there is a triclinic modification
of K Ta S [14], which was not observed for Nb. Another
4
2 11
interesting finding is that only one structural modification
was reported for K Nb S (space group C2/c), whereas
K Nb2.97Ta1.03S25 (3): The procedure for the synthesis of
6
6
4
22
K Ta S is dimorphic and crystallizes in space groups
4 22
3 is the same as that for 2 except that the molar ratio was
changed to 3:3:1:14. The melt contained red polyhedral
crystals in a 90% yield. The crystals are stable in dry air for
several weeks. The EDX analysis of selected single crystals
indicated the presence of all four elements (K, Nb, Ta, S) in
an atomic ratio of 6:3:1:25.
6
C2/c and P2 /c under different reaction conditions [17]. A
1
similar observation was made for A M S . The compound
6
4 25
Rb Ta S crystallizes in C2/c whereas space group P2 /n
1
6
4
25
was adopted by K Nb S . These examples demonstrate
6
4 25
the different structural behavior of Nb and Ta sulfides
mainly prepared in polysulfide fluxes. After the successive
substitution on the Nb sites (i.e. K Nb0.96Ta1.04S11 [40]), we
K Cu Nb0.98Ta1.02S8 (4) and KCu Nb0.53Ta0.47S4 (5):
3
3
2
Crystals were prepared by reacting a mixture of K S , Cu,
2 3
4
started to investigate the effect of partial substitution based
on K TaS , K Nb S , K Nb S , K Cu Nb S , and
KCu NbS structure types. In this paper we report the
Nb, Ta, S with a molar ratio of 2:4:1:1:7. After being sealed
ꢀ
3
in a silica tube under vacuum (ꢁ2 ꢂ 10 mbar), the
starting material was heated to 600 1C, held there for 6
days, and cooled down to 100 1C at a rate of 2 1C/h,
followed by cooling to room temperature in 4 h. After
removing excess K S flux with DMF followed by washing
3
4
6
4
22
6
4
25
3
3
2 8
2
4
syntheses, crystal structures, and characterizations of
K V0.32Ta0.68S , K Nb1.07Ta2.93S , K Nb2.97Ta1.03S ,
K Cu Nb0.98Ta1.02S , and KCu Nb0.53Ta0.47S .
3
4
6
22
6
25
3
3
8
2
4
2 x
with acetone, transparent brown needles (4: 40%) and
transparent green needles (5: 40%) were obtained. Both
compounds are stable in dry air for several months.
The EDX analyses of single crystals indicated the
presence of all five elements (K, Cu, Nb, Ta, S) in an
atomic ratio of 3:3:1:1:8 for compound 4 and 2:4:1:1:8 for
compound 5.
2
. Experimental
2
.1. Reagents
The following reagents were used as obtained unless
noted: (i) K metal, 99.95%, ABCR GmbH & Co.KG;
ii) S, 99.99%, Heraeus; (iii) Nb powder, 99.8%, 325 mesh,
(
Alfa Aesar; (iv) Ta powder, 99.98%, 325 mesh, ABCR
GmbH & Co.KG; (v) Cu powder, 99.5%, 200 mesh, Alfa
Aesar; (vi) V powder, 99.7%, 325 mesh, Heraeus.
2.3. X-ray crystallography
All single crystal X-ray investigations were performed
using an imaging plate diffraction system (IPDS) (MoKa-
˚
2
.2. Synthesis
radiation; l ¼ 0.71073 A) equipped with a low-temperature
device from Oxford Cryosystem. The crystals were
mounted on top of glass fibers and bathed in cold nitrogen
stream during data collection. The raw intensities were
treated in the normal way applying Lorentz, polarization,
and numerical absorption corrections. All structures
The compound K S was prepared from the reaction of
2
3
stoichiometric amounts of elemental K and S powder in
liquid ammonia under an argon atmosphere.
K V0.32Ta0.68S (1): K S , V, Ta, and S in a 4/2/1/8
3
4
2 3
molar ratio were thoroughly mixed in a nitrogen-filled
glove box. The mixture was then loaded into a glass
were solved with direct methods using SHELXS-97 and
2
refined against F using SHELXL-97 of Shelxtl program
o
s
ampoule (Duran ), which was subsequently evacuated
package [41].
On the basis of the systematic absences the space groups
Pnma for 1, P2 /c for 2, P2 /n for 3, C2/c for 4, and Ama2
ꢀ
3
(
ꢁ2 ꢂ 10 mbar) and flame sealed. The ampoule was
heated from 25 to 500 1C in 24 h and kept at this
temperature for 6 days, cooled to 100 1C at a rate of
1
1
for 5 were chosen. After successful assignments of the high
electron density peaks as Ta, (Cu), K, and S atoms, the
displacement parameters and occupancy on each atomic
site were examined. For all compounds the S atom sites are
fully occupied with reasonable displacement parameters.
The refined occupancies of heavy metal sites, initially
assigned to Ta, were significantly low indicating that lighter
atoms V or Nb are also involved in this site. Therefore,
disorder models were applied by introducing V or Nb
atoms so that the sum of the occupancies were set equal to
full occupancy to maintain charge balance. The other sites
were found suitable for K atoms and/or Cu atoms based
on the observed electron densities. After successive
2
1C/h followed by cooling to room temperature in 4 h.
The resulting black melt was washed with DMF and
acetone and the product was dried in vacuum. The product
consists of black platelet crystals (yield ꢁ50%). The
crystals are stable in dry air for several weeks, but
decompose slowly under humid conditions. An EDX
analysis of single crystals indicated the presence of all four
elements (K, V, Ta, S) in an approximate atomic ratio of
9
:1:2:12.
K Nb1.07Ta2.93S22 (2): The preparation and isolation
6
process of 2 were similar to those of 1. However, the
mixture of K S , Nb, Ta, S (molar ratio: 3:1:3:14) was
2
3

ARTICLE IN PRESS
Y. Wu, W. Bensch / Journal of Solid State Chemistry 180 (2007) 2166–2174
2168
refinements of the positional parameters and site occupa-
tion factors (SOF) of all atom sites, reasonable displace-
ment parameters for all atoms were obtained, as well as low
residual electron densities. The final formulae were refined
as K V0.32(1)Ta0.68(1)S for 1, K Nb1.07(1)Ta2.93(1)S22 for 2,
2.4. Physical measurements
Raman spectroscopy: Raman spectra were collected on
an ISF-66 spectrometer (Bruker) with additional FRA 106
Raman module. A Nd/YAG laser was used as the source of
excitation (l ¼ 1064 nm). The samples were ground and
prepared on Al sample holders. The measuring range was
3
4
6
K Nb2.97(1)Ta1.03(1)S25 for 3, K Cu Nb0.98(1)Ta1.02(1)S8 for
6
3
3
4
, and KCu Nb0.53(1)Ta0.47(1)S4 for 5. The SOFs of V/Ta or
2
ꢀ
1
ꢀ1
Nb/Ta show a ratio near 1:2 in compounds 1, 2, and 3, and
:1 in compounds 4, 5, which may indicate a certain kind of
from ꢀ1000 to 3500 cm with a resolution of 2 cm
.
1
Solid-state UV/vis/NIR spectroscopy: Spectra were
recorded on a Cary 5 spectrometer (Varian Techtron
Pty.). The spectrometer was equipped with an Ulbricht
sphere (Diffuse reflectance accessory; Varian Techtron
Pty.). The inner wall of the Ulbricht sphere (diameter
110 mm) was covered with a PTFE layer of 4 mm thickness.
A PbS detector (NIR) and a photomultiplier (UV/vis) were
attached to the Ulbricht sphere.
ordering. Long exposed images gave no hints for super-
structures.
Technical details of the data acquisition as well as some
refinement results are summarized in Table 1.
Further details of the crystal structure investigation can
be ordered referring to the No CSD-417842 (K V0.32(1)
3
Ta0
S ), CSD-417843 (K Nb1.07(1)Ta
6
S ), CSD-
S ), CSD-417841 (K Cu Nb
0.98(1)
.68(1) 4
2.93(1) 22
417844 (K Nb2.97(1)Ta
Ta1
The samples were ground together with BaSO4 and
prepared as a flat specimen of approximate 2 mm thickness.
Resolution was 1 nm for the UV/vis range and 2 nm for the
near-IR range. The measuring range was 250–2000 nm.
6
1.03(1) 25
3
3
S ), CSD-417845 (KCu Nb0.53(1)Ta
2
S ), the
0.47(1) 4
.02(1) 8
authors and the citation of this paper at the Fachinforma-
tionszentrum Karlsruhe, Gesellschaft fur wissenschaftlich-
¨
technische Information mbH. D-76344 Eggenstein-Leopold-
shafen (Germany). E-mail: crysdata@fiz-karlsruhe.de
BaSO was used as white standard for 100% reflectance.
4
Absorption data were calculated from the reflectance data
Table 1
Technical details of data acquisition and some refinement results
Compound
1
2
3
4
5
Formula
Crystal system
Space group
K
3
V
0.32Ta0.68
S
4
K
6
Nb1.07Ta2.93
S
22
K
6
Nb2.97Ta1.03
S
25
K
3
Cu
3
Nb0.98Ta1.02
S
8
2 4
KCu Nb0.53Ta0.47S
Orthorhombic
Pnma
Monoclinic
P2 /c
Monoclinic
P2 /n
Monoclinic
C2/c
Orthorhombic
Ama2
1
1
˚
a (A)
5.2354(7)
10.6920(6)
9.2991(5)
–
7.6412(4)
8.7572(5)
24.5753(14)
98.559(6)
1626.2(2)
2
15.7147(10)
12.9840(9)
18.2363(12)
104.123(8)
3608.5(4)
4
23.5934(19)
5.5661(2)
14.2373(12)
120.631(9)
1608.8(2)
4
7.4615(4)
18.2902(16)
5.5320(6)
–
˚
b (A)
˚
c (A)
b (deg)
˚
V (A)
918.24(10)
4
170
754.96(11)
4
170
Z
T (K)
293
3.205
293
2.759
170
3.467
ꢀ
3
Calcd. den. (g cm
m Mo (mm
F(0 0 0)
)
2.785
10.674
3.780
14.842
789
ꢀ
1
)
12.375
1448
6.184
2944
13.253
1546
713
61p2yp561
ꢀ12php12
2
y range (deg)
Index range
51p2yp561
ꢀ8php10
ꢀ11pkp11
ꢀ32plp32
3900
51p2yp561
ꢀ20php20
ꢀ17pkp17
ꢀ23plp24
8549
61p2yp561
ꢀ30php30
ꢀ7pkp6
ꢀ18plp18
1908
71p2yp561
ꢀ10php10
ꢀ25pkp25
ꢀ7plp7
1184
ꢀ
ꢀ
14pkp13
12plp12
Indep. refl.
Refl. [F
1170
o
44s(F
o
)]
1128
3353
0.0322
7199
0.0503
1805
0.0291
1143
0.0360
R
int
0.0438
0.1499/0.3231
45
Min/max. transm.
No. of parameters
0.1576/0.2172
148
0.0438
0.3416/0.4631
321
0.0600
0.1279/0.2292
77
0.0579
0.1278/0.1858
47
0.0689
a*
b*
0.0577
3.9
0
0.0269
22.1
0.0417
4.8
0.0296
0
0.0332
R
1
for F
wR for all data
GooF
Flack parameter x
o
44s(F
o
)
0.0330
0.0894
1.120
2
0.0621
0.992
0.1113
1.034
0.0802
1.077
0.0970
1.201
–
–
–
–
ꢀ0.09(3)
1.964/ꢀ1.862
ꢀ3
˚
Dr(eA
)
1.596/ꢀ2.073
1.092/ꢀ1.689
5.359/ꢀ1.893
2.311/ꢀ1.668
R
1
¼ SJF
wR
¼ [Sw(F
where P ¼ (max (F
o
jꢀjF
c
J/SjF
o
j.
2
2 2
2 2 1/2
2 2
o
)+(a*P) +b*P],
2
o
ꢀF
c
) /Sw(F
o
) ] , w ¼ 1/[s(F
2
2
o
c
,0)+2F )/3.

ARTICLE IN PRESS
Y. Wu, W. Bensch / Journal of Solid State Chemistry 180 (2007) 2166–2174
2169
+
(M ¼ V/Ta) anions and K cations. The M (V/Ta) atom is
using the Kubelka–Munk function [42]. The approximate
band gap was determined as the intersection point between
the energy axis and the line extrapolated from the linear
tetrahedrally coordinated, and the M–S distances
˚
(2.2269(13) to 2.2394(16) A) are somewhat smaller than
2
part of the absorption edge in a (F(R)) vs. energy plot.
those in K TaS [10] and longer than in K VS [3] due to
3
4
3
4
the partial substitution of Ta by V. The S–M–S angles
(
(
108.58(6) to 111.77(7)1) are close to the tetrahedral value
109.471). The two crystallographically independent K
3
. Results and discussion
+
ions are coordinated by seven S atoms in an irregular
˚
polyhedron (cutoff for K–S distances: 4.0 A). K(1) is linked
3
.1. Crystal structure
to four symmetry-related MS tetrahedra whereas K(2) is
4
connected to five. The distances for K(1)–S and K(2)–S
The crystal structure of K V0.32Ta0.68S4 (1) is shown in
3
Fig. 1. K V0.32Ta0.68S is isostructural to the A MQ family
3
4
3
4
˚
range from 3.196(2) to 3.515(2) A (average 3.319(2) A) and
˚
of compounds, where A ¼ K, Rb, Cs; M ¼ V, Nb, Ta;
˚
˚
3
4
ꢀ
from 3.121(2) to 3.736 A (average 3.430(2) A), respectively.
These distances are also shorter than those in K TaS [10].
Q ¼ S, Se [3–11]. It is built from the packing of MS
3
4
In the structure of K Nb1.07Ta
S
(2) which is isostruc-
tural to the second modification of K Ta S [17], discrete
[
6
2.93 22
6
4 22
6
ꢀ
+
M S ] anions and K cations are found (Fig. 2). Each
4 22
6ꢀ
[M S ] anion is composed of two M S building blocks
linked via terminal sulfur ligands. The coordination mode of
4 22 2 11
6ꢀ
2
[
M S ]
4
(Fig. 3) can be described as [(M (mꢀZ ,
22
2
1
2
1
6ꢀ
6ꢀ
Z ꢀS ) (Z ꢀS )(S) ) (mꢀZ ꢀS )] . Within the [M S ] an-
2
3
2
2 2
2
4 22
˚
ion, each nonbonding M pair (M–M distance 3.5499(3) A) is
2ꢀ
bridged by three S ligands with an average M–S distance of
2.471(2) A and S–S bonds of 2.087(2) A. Each M atom is
bound to a terminal S anion to form a relatively short M–S
2
˚ ˚
˚
bond (average: 2.237(2) A). The coordination sphere of the M
2
ꢀ
atoms is completed by the addition of two S ligands (S–S
˚
2
2
2
ꢀ
distance ¼ 2.090(2) A) per M pair. One S ligand is bound to
2
2ꢀ
an M atom in a typical Z –fashion while the second S links
2
the other M atom to a neighboring dimer yielding a tetrameric
anion with M in the +5 oxidation state. The M–S distances,
M–M separation, and S–S bond lengths are nearly identical to
those of K Ta S (II) [17].
6
4 22
+
The structure of K Nb2.97Ta1.03S (3) consists of K
cations and [M S ] (M ¼ Nb/Ta) anions (Fig. 4), and is
Fig. 1. Crystal structure of K
along [0 0 1].
3
V
0.32Ta0.68
S
4
(1) with perspective view
6
25
6
ꢀ
4
25
6
Fig. 2. Crystal structure of K Nb1.07Ta2.93S22 (2) with perspective view along [1 0 0].

ARTICLE IN PRESS
Y. Wu, W. Bensch / Journal of Solid State Chemistry 180 (2007) 2166–2174
2170
Fig. 3. [M
4
S
22] units in the structure of K
6
Nb1.07Ta2.93
S22 (2) with atomic labeling. The ellipsoids are drawn at the 50% probability level.
˚
(
3.322–3.479 A) match well with the sum of the ionic radii
+
2ꢀ
of K and S
K Cu Nb0.98Ta1.02S (4) is isostructural to K Cu M S
2 8
.
3
3
8
3
3
(
M ¼ Nb, Ta) [30] and the structure is composed of anionic
1 3ꢀ
chains [Cu M S ]
(M ¼ Nb/Ta) being separated by
ions (Fig. 5). The chains are directed along [0 1 0]
Fig. 6) with the shortest interchain separation of
N
3
2 8
+
K
(
˚
3.632(1) A between S(4) atoms of adjacent chains. Within
the chains the unique M atom and the two independent Cu
atoms are tetrahedrally coordinated by S atoms. The MS4
and Cu(2)S tetrahedra share common edges along [0 1 0]
4
to form the infinite one-dimensional [CuMS ] chains. Two
4
adjacent chains are interconnected by Cu(1)S tetrahedra
4
in such way that the Cu(1)S tetrahedra have common
4
Fig. 4. [M
4
S
25] units in the structure of K
6
Nb2.97Ta1.03
S
25 (3) with atomic
edges with MS4 tetrahedra along [1 0 0] and common
corners with Cu(2)S tetrahedra. Since there are no S–S
labeling. The ellipsoids are drawn at the 50% probability level.
4
interactions the formal oxidation states K(+1), Cu(+1),
M(+5), and S(ꢀ2) can be assigned. Similar copper—group
5 metal—chalcogen chains were found previously in
K Cu M S (M ¼ Nb, Ta) [30]. The mean Cu–S distances
isostructural to K Nb S [22]. One anion is composed of
6
4 25
two M2S11 subunits, which are connected by a S chain.
3
3
3
2 8
6
The coordination mode of the resulting [M S ] anion
ꢀ
are longer than the analogous bonds in K Cu Nb S
3 3 2 8
4
25
2
2
1
can be described as [(M (m ꢀZ ,Z –S ) (Z –S )(S) )
whereas the mean M–S bond lengths are almost the same
as those in K Cu Nb S .
The compound KCu Nb0.53Ta0.47S4 (5) crystallizes iso-
2
2
2 3
2
2 2
1
1
6ꢀ
5
(
m ꢀZ ,Z –S )] . Each M atom has a short bond to the
2ꢀ
˚
2
3
3
2 8
axial S
(S(1) and S(10)) of about 2.2 A. Five M–S
2
˚
separations scatter around 2.4 A, and finally a long
structural to KCu NbS [31] (Fig. 7). It is composed of
4
2
ꢀ
˚
interatomic M–S distance of about 2.9 A is observed to a
two-dimensional [Cu MS ] layers, which are parallel to
2 4
+
the (0 1 0) plane and K ions located between the layers.
˚
The shortest interlayer S–S distance of 3.776(1) A is longer
2
2ꢀ
S atom of a Z –S anion attached to the neighbored M
2
atom. The long M–S distances are always in trans position
to the short M–S bonds (Fig. 4). The M–S distances match
well with those reported for K Nb S [22] and Rb Ta S
4 25
than the sum of the van der Waals radii of S. Obviously
there are no interactions between the adjacent layers.
6
4
25
6
2
2
ꢀ
ꢀ
[20]. The S–S bonds in the S anions are between 2.036(2)
˚
and 2.099(2) A (average 2.072 A), typical for S–S single
Within the [Cu MS ] layers (Fig. 8), M and Cu atoms are
2
4
˚
tetrahedrally coordinated by S atoms. Alternating MS and
4
˚
bonds. The shortest M–M distance amounts to 3.574(2) A,
Cu(1)S4 tetrahedra share common edges to form
[Cu(1)MS ] chains along [0 0 1], like the one-dimensional
which is too long for significant metal to metal interactions.
2
4
ꢀ
The angles S–S–S in the S anion vary between 107.1(1)1
chains in K CuNbS [25]. The Cu(2)S tetrahedra share
2
5
4
4
and 108.8(1)1 and are near the expected tetrahedral angles.
The six crystallographically independent K ions are
coordinated by 9 or 11 S atoms with K–S distances varying
common corners with the Cu(1)S tetrahedra along [1 0 0]
4
+
and have common edges with MS tetrahedra along [1 0 0].
4
ꢀ
This connection mode yields the [Cu MS ] layers. The
2
4
˚
from 3.083(2) to 3.794(2) A. The average K–S separations
˚
M–S bond lengths (2.283(2)–2.335(3) A) match well with

ARTICLE IN PRESS
Y. Wu, W. Bensch / Journal of Solid State Chemistry 180 (2007) 2166–2174
2171
Fig. 5. Crystal structure of K
3
Cu
3
8
Nb0.98Ta1.02S (4).
˚
.372(2) A) in 4. The S–Cu–S angles about the two
2
crystallographically independent Cu atoms are different.
The S–Cu(1)–S angles are close to the normal tetrahedral
value (105.66(6)–113.01(5)1), while the S–Cu(2)–S angles
scatter from 104.85(5)1 to 117.29(6)1, which clearly
indicates the stronger distortion of the Cu(2)S tetrahe-
4
+
dron. The K ions are coordinated by nine S atoms
˚
choosing a cutoff of 4.0 A for the K–S distances. The K–S
˚
distances range from 3.400(3) to 3.778(1) A (average:
˚
.564(2) A). The formal oxidation states of all atoms in
3
this compound can be assigned as K(+1), Cu(+1),
M(+5), and S(ꢀ2).
3.2. Optical properties
3ꢀ
Fig. 6. [Cu M
3
2
S
8
]
3 3 8
chain in the structure of K Cu Nb0.98Ta1.02S (4)
with atomic labeling. The ellipsoids are drawn at the 50% probability
level.
The FT-Raman spectra of K V0.32Nb0.68S4 (1) in the
3
ꢀ
1
range 100–550 cm
spectrum shows shifts at 486, 468, 445, 405, 205, 183, and
are shown in Fig. 9. The Raman
ꢀ
1
33 cm . The energy shifts at 486, 468, 445, and 405 cm
ꢀ1
1
can be assigned to M–S stretching vibrations, whereas
ꢀ
1
vibrations at 205, 183, and 133 cm are related to the
S–M–S deformation modes of MS tetrahedra. Due to the
4
˚
shorter M–S bond length (2.227(1) A), the stretching
vibration are located at higher energy compared to the
˚
data of Tl TaS (Ta–S: 2.35 A) [43].
3
4
Fig. 10 shows the FT-Raman spectrum of
K Nb1.07Ta2.93S22 (2). It displays resonances at 508, 466,
6
4
1
49, 435, 344, 304, 289, 278, 255, 235, 202, 181, 166, 147,
ꢀ
1
36, 116, and 94 cm . Unfortunately, no Raman data
were reported for A M S (A ¼ K, Rb, Cs; M ¼ Nb, Ta),
6
4 22
and the effect of partial substitution cannot be directly
compared. Compared with the Raman spectrum of
K Ba (Nb S ) [39], the spectrum of 2 is more complex.
4
2
2 11 2
The S–S stretching mode (n(S–S)) of the disulfide ligands at
ꢀ
1
508 cm
with a shoulder at lower energy is the most
intense band. For K Ta S [24], the n(S–S) mode occurs at
2
2 10
ꢀ
1
11 and 505 cm supporting the assignment. The peaks at
5
4
Fig. 7. Perspective view of the structure of KCu
0 0 1].
2 4
Nb0.53Ta0.47S (5) along
ꢀ
1
66, 449, and 435 cm
are due to symmetric n (M–S)
[
s
stretching vibrations of the terminal sulfide ions. In the
Raman spectrum of K Ba (Nb S ) this mode shows a
4
2
2 11 2
those in compound 4. The S–M–S angles vary from
07.61(5)1 to 112.38(6)1, close to the normal tetrahedral
bathochromic shift. The difference of the energetic position
of this band may be due to the presence of Nb/Ta in
1
values. The Cu–S bonds from 2.334(2) to 2.359(2) A
are slightly shorter than the Cu–S distances (2.346(2)–
ꢀ
1
compound 2. The bands at 344, 304 cm are assigned to
˚
the symmetric n (M–S ) stretching mode of M–S–M
s
m

ARTICLE IN PRESS
Y. Wu, W. Bensch / Journal of Solid State Chemistry 180 (2007) 2166–2174
2172
ꢀ
1
bridges whereas the bands at 289, 278, 255, 235 cm are
due to the mixed M–S vibrations. The peaks below
ꢀ
1
02 cm may be caused by S–M–S bending or deforma-
2
tion modes.
In the Raman spectrum three resonances are observed at
12, 494, 474, 464, 441, 353, 329, 295, 272, 245, 218, 192,
5
1
ꢀ
1
76, 150, 131, 116, and 105 cm (Fig. 11). The n (M–S )
s
t
ꢀ
1
stretching vibration at 474 cm is the most intense band.
ꢀ
1
The S–S stretching vibrations occur at 512, 494 cm , the
ꢀ
1
M–S vibrations at 353–218 cm , and S–M–S deformation
ꢀ
1
modes below 200 cm
The FT-Raman spectrum of K Cu Nb0.98Ta1.02S8 (4) is
.
3
3
displayed in Fig. 12. The Raman spectrum shows shifts at
ꢀ
1
56, 445, 425, 415, 264, 232, 194, 139, 109, and 93 cm . In
4
accordance to our previous work [31], the resonances at
ꢀ
1
456, 425, and 415 cm may be assigned to M–S symmetric
ꢀ
2 4 2 4
MS ] layer in the structure of KCu Nb0.53Ta0.47S
Fig. 8. Part of the [Cu
5) with atomic labeling. The ellipsoids are drawn at the 50% probability
level.
ꢀ
1
stretching vibrations, the peak at 445 cm to an asym-
1
metric mode. The shifts at 264, 232, and 194 cm can be
(
ꢀ
Fig. 9. Raman spectra of K
3
V
0.32Ta0.68
S
4
(1).
Fig. 11. Raman spectrum of K Nb2.97Ta1.03S25 (3).
6
Fig. 10. Raman spectrum of K
6
Nb1.07Ta2.93S22 (2).
3 3 8
Fig. 12. Raman spectra of K Cu Nb0.98Ta1.02S (4).

ARTICLE IN PRESS
Y. Wu, W. Bensch / Journal of Solid State Chemistry 180 (2007) 2166–2174
2173
presence of Nb and Ta in the structures of compounds 2
and 3 decreases the band gap by about 0.3 eV.
In conclusion, five compounds K V0.32Ta0.68S4 (1),
3
K Nb1.07Ta2.93S (2), K Nb2.97Ta1.03S (3), K Cu Nb
0.98
6
22
6
25
3
3
Ta1.02S8 (4), and KCu Nb0.53Nb0.47S4 (5) have been
2
synthesized under different conditions. The mixed com-
pound K Nb1.07Ta2.93S22 crystallizes in space group P2 /c,
6
1
a modification that was only observed for the pure Ta
compound. In K Nb2.97Ta1.03S25 the Nb content seems to
6
determine the actual structure type and the material adopts
space group P2 /n, which was also reported for the pure
1
Nb sample in contrast to the pure Ta compound crystal-
lizing in C2/c.
Attempts to synthesize new compounds with different V/
Nb, V/Ta, and Nb/Ta ratios were unsuccessful except the
presented examples 1–5 and K Nb0.96Ta1.04S11 [39]. During
4
the syntheses the ratios of the transition metals in the flux
were varied over a large range. According to EDX
analyses, the final products contained the metals in ratios
very close to that given in the manuscript. Interestingly,
compound 1 could only be obtained applying a large S
excess. We cannot exclude that compounds with different
metal atom ratios can be prepared changing for instance
the reaction temperature. In many cases the Rb and Cs
analogs of K-containing compounds were reported. But all
attempts to prepare analogous Rb and Cs compounds were
not successful.
2 4
Fig. 13. Raman spectra of KCu Nb0.53Ta0.47S (5).
Acknowledgments
Financial support by the State of Schleswig-Holstein, the
Fonds der Chemischen Industrie (FCI), and DFG
(Deutsche Forschungsgemeinschaft) is gratefully acknowl-
edged.
Appendix A. Supplementary materials
Fig. 14. Transformed reflectance spectra of compounds 2–5.
Supplementary data associated with this article can be
found in the online version at doi:10.1016/j.jssc.
2007.05.015.
assigned to the Cu–S valence vibrations and S–M(Cu)–S
deformation modes, respectively. The assignment of peaks
at lower energy is still not clear.
In the Raman spectrum of KCu Nb0.53Ta0.47S4 (5),
2
References
resonances at 451, 436, 421, 406, 273, 221, 194, 149, 138,
ꢀ
1
25, 118, and 97 cm are seen (Fig. 13). The patterns are
1
[
1] M.G. Kanatzidis, Chem. Mater. 2 (1990) 353–363.
[2] M.G. Kanatzidis, A.C. Sutorik, Prog. Inorg. Chem. 43 (1995)
51–265.
3] P. Durichen, W. Bensch, Eur. J. Solid State Inorg. Chem. 33 (1996)
09–320.
4] M. Emirdag-Eanes, J.A. Ibers, Z. Kristallogr.—NCS 216 (2001)
89–490.
[5] K.O. Klepp, G. Gabl, Eur. J. Solid State Inorg. Chem. 34 (1997)
143–1154.
6] R. Niewa, G.V. Vajenine, F.J. DiSalvo, J. Solid State Chem. 139
1998) 404–411.
7] M. Latroche, J.A. Ibers, Inorg. Chem. 29 (1990) 1503–1505.
ther, I. Jess, W. Bensch, Acta Crystallogr. C 54
very similar to those of compound 4 allowing an identical
assignment of the different modes (see above).
The compounds 2–5 exhibit well-defined electronic
absorption spectra with sharp optical absorption edges
associated with energy gaps of 1.88 eV for compound 2,
1
[
[
¨
3
4
2
2
.01 eV for compound 3, 2.61 eV for compound 4, and
.50 eV for compound 5 (Fig. 14). The optical absorptions
1
[
[
are likely due to charge-transfer transitions from filled
S-based p-orbitals to empty M-based orbitals. Compared
to available data for A Ta S (A ¼ K, Rb) (E ¼ 2.21 eV)
(
4
4
22
g
[8] O. Krause, C. Na
¨
and Rb Ta S
(E ¼ 2.35 eV) [44], the simultaneous
(1998) 902–904.
6
4
25
g

ARTICLE IN PRESS
Y. Wu, W. Bensch / Journal of Solid State Chemistry 180 (2007) 2166–2174
2174
[
9] S. Herzog, C. Na
Chem. 624 (1998) 2021–2024.
10] S. Herzog, C. Nather, W. Bensch, Acta Crystallogr. C 54 (1998)
742–1744.
11] B. Deng, J.A. Ibers, Acta Crystallogr. E 60 (2004) i147–i148.
12] W. Bensch, P. Durichen, Eur. J. Solid State Inorg. Chem. 33 (1996)
27–536.
13] K.O. Klepp, G. Gabl, Z. Naturforsch. 53b (1998) 1236–1238.
14] S. Herzog, C. Nather, W. Bensch, Z. Anorg. Allg. Chem. 625 (1999)
69–974.
15] S. Schreiner, L.E. Aleandri, D. Kang, J.A. Ibers, Inorg. Chem. 28
1989) 392–393.
16] P. Durichen, W. Bensch, Acta Crystallogr. C 54 (1998) 706–708.
17] P. Stoll, C. Nather, W. Bensch, Z. Anorg. Allg. Chem. 628 (2002)
489–2494.
18] W. Bensch, P. Du
19] P. Stoll, C. Nather, I. Jess, W. Bensch, Z. Anorg. Allg. Chem. 626
2000) 959–962.
20] P. Stoll, C. Na
63–568.
21] P. Stoll, C. Na
e368–e369.
22] W. Bensch, P. Du
233–1240.
23] W. Bensch, C. Na
33–135.
24] Y. -D. Wu, C. Na
569–1574.
25] W. Bensch, P. Du
33–933.
¨
ther, P. Du
¨
richen, W. Bensch, Z. Anorg. Allg.
[27] R. Tillinski, C. Na
333–334.
[28] C. Rumpf, R. Tillinski, C. Na
Eur. J. Solid State Inorg. Chem. 34 (1997) 1187–1198.
[29] W. Bensch, P. Durichen, C. Weidlich, Z. Kristallogr. 211 (1996),
931–931.
¨
ther, W. Bensch, Acta Crystallogr. C57 (2001)
[
¨
¨
¨
ther, P. Durichen, I. Jess, W. Bensch,
1
[
[
¨
¨
5
[30] Y.-J. Lu, J.A. Ibers, J. Solid State Chem. 98 (1992) 312–317.
[31] Y.-J. Lu, J.A. Ibers, J. Solid State Chem. 94 (1991) 381–385.
[
[
¨
[32] Y.-D. Wu, C. Na
1006–1014.
[33] W. Bensch, P. Du
¨
ther, W. Bensch, Z. Naterforsch. 59b (2004)
9
[
¨
richen, Chem. Ber. 129 (1996) 1207–1210.
(
¨
¨
[34] R. Tillinski, C. Rumpf, C. Nather, P. Durichen, I. Jess, S.A. Schunk,
[
[
¨
W. Bensch, Z. Anorg. Allg. Chem. 624 (1998) 1285–1290.
[35] W.-T. Chen, H.-W. Ma, G.-C. Guo, L. Deng, G.-W. Zhou,
Z.-C. Dong, J.-S. Huang, Bull. Chem. Soc. Jpn. 77 (2004)
505–509.
¨
2
[
[
¨
richen, Z. Anorg. Allg. Chem. 622 (1996) 1963–1967.
¨
[36] K.O. Klepp, G. Gabl, Eur. J. Solid State Inorg. Chem. 34 (1997)
1119–1131.
(
[
[
[
[
[
[
[
¨
ther, I. Jess, W. Bensch, Solid State Sci. 2 (2000)
[37] O. Krause, P. Du
(2000) 197–203.
[38] O. Krause, P. Du
Inorg. Chem. (1999) 1295–1299.
¨
richen, C. Na
¨
ther, W. Bensch, Solid State Sci. 2
5
¨
ther, I. Jess, W. Bensch, Acta Crystallogr. C 56 (2000)
¨
richen, C. Nather, W. Bensch, Eur. J. Solid State
¨
¨
richen, Eur. J. Solid State Inorg. Chem. 33 (1996)
[39] Y.-D. Wu, C. Na
(2005) 1062–1069.
[40] Y.-D. Wu, C. Na
i208–i210.
¨
ther, N. Lehnert, W. Bensch, Solid State Sci. 7
1
¨
ther, P. Du
¨
richen, Angew. Chem. 37 (1998)
¨
ther, W. Bensch, Acta Crystallogr. E. 61 (2005)
1
¨
ther, W. Bensch, J. Solid State Chem. 178 (2005)
richen, C. Weidlich, Z. Kristallogr. 211 (1996),
[41] A. Bruker, SHELXTL Version 5.1, Bruker AXS Inc. Madison,
Wisconsin, USA, 1998.
[42] P. Kubelka, F. Munk, Z. Tech. Phys. 12 (1931) 593–601.
1
¨
9
[43] K.H. Schmidt, A. Mu
(1972) 275–282.
[44] P. Stoll, Ph.D. Dissertation, University Kiel, 2002.
¨
ller, J. Bouwma, F. Jellinek, J. Mol. Struct. 11
26] K. Peters, E.-M. Peters, H.G. von Schnering, C. Mujica, G. Carvajal,
J. Llanos, Z. Kristallogr. 211 (1996), 812–812.