Syntheses, crystal structures and spectroscopic properties of Ag2Nb[P2S6][S2] and KAg2[PS4]

Article abstract of DOI:10.1016/j.jssc.2008.11.017

Ag₂Nb[P₂S₆][S₂] (1) was obtained from the direct solid state reaction of Ag, Nb, P₂S₅ and S at 500 °C. KAg₂[PS₄] (2) was prepared from the reaction of K₂S

Full text of DOI:10.1016/j.jssc.2008.11.017

ARTICLE IN PRESS
Journal of Solid State Chemistry 182 (2009) 471–478
Contents lists available at ScienceDirect
Journal of Solid State Chemistry
journal homepage: www.elsevier.com/locate/jssc
Syntheses, crystal structures and spectroscopic properties of Ag Nb[P S ][S ]
2
2 6
2
and KAg [PS ]
2
4
Ã
Yuandong Wu, Wolfgang Bensch
Institut f u¨ r Anorganische Chemie, Universit a¨ t Kiel, Olshausenstr. 40, D-24098 Kiel, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
2 2 6 2 2 5
Ag Nb[P S ][S ] (1) was obtained from the direct solid state reaction of Ag, Nb, P S and S at 500 1C.
Received 5 September 2008
Received in revised form
2 4 2 3 2 5
KAg [PS ] (2) was prepared from the reaction of K S , Ag, Nd, P S and extra S powder at 700 1C.
Compound 1 crystallizes in the orthorhombic space group Pnma with a ¼ 12.2188(11), b ¼ 26.3725(16),
2
8 October 2008
3
˚
˚
c ¼ 6.7517(4) A, V ¼ 2175.7(3) A , Z ¼ 8. Compound
tetragonal space group I 4¯ 2m with lattice parameters a ¼ 6.6471(7), c ¼ 8.1693(11) A, V ¼ 360.95(7) A ,
Nb[P ][S ] (1) consists of [Nb 12], [P ] and new found puckered [Ag
2 crystallizes in the non-centrosymmetric
Accepted 2 November 2008
Available online 21 November 2008
3
˚
˚
Z ¼ 2. The structure of Ag
2
2
S
6
2
2
S
2
S
6
2 4
S ]
Keywords:
chains which are along [001] direction. The Nb atoms are located at the center of distorted bicapped
Silver
2ꢀ
trigonal prisms. Two prisms share square face of two [S
2
] to form one [Nb
2
S
12] unit, in which Nb–Nb
] units to form
] tetrahedra and
] triangles that share corners with each other. These chains are connected with [P ] units and
12] units to form three-dimensional frame work. The structural skeleton of 2 is built up from
] and [PS ] tetrahedra linked by corner-sharing. The three-dimensional anionic framework
Thiophosphates
Crystal structure
Spectroscopic properties
2ꢀ
bond is formed. The [Nb
4-membered rings. The novel puckered [Ag
AgS
Nb
AgS
2
S
12] units share all S
corners with ethane-like [P S
2 6
1
2 4 4
S ] chains are composed of distorted [AgS
[
[
[
3
2 6
S
2
S
4
4
contains orthogonal, intersecting tunnels directed along [100] and [010]. This compound possesses a
compressed chalcopyrite-like structure. The structure is compressed along [001] and results from eight
+
coordination sphere for K . Both compounds are characterized with UV/vis diffuse reflectance
spectroscopy and compound 1 with IR and Raman spectra.
&
2008 Elsevier Inc. All rights reserved.
1
.
Introduction
isolated if one is substituted by Cu or Ag cations. Phases such as
CuMP
(M ¼ V, Cr, In) [27–31] are obtained, whereas different
stoichiometries are observed with larger alkali cations, for
example, NaV1ꢀx [32], NaCrP [33], AMP (A ¼ K, Rb, Cs;
M ¼ Cr, V, In) [34–36], K VP [37], A Cr [PS (A ¼ Na, K)
2 6
S
Transition metal thiophosphates form a wide and interesting
class of compounds that has been the subject of numerous
investigations because of their broad structural variety [1] and
their physical properties. Well-known examples of transition
P
2
S
6
2
S
6
2 7
S
4
2
S
9
3
2
4 3
]
[38,39]. The explorative investigation of rare earth(III) chalcogo-
phosphates revealed a fascinating variety of many quaternary
compounds with structures ranging from isolated ions to three-
dimensional networks [40]. In the neodymium case, six thiopho-
metal thiophosphates include layered MPS
Co, Ni, Hg, Mg, Ca, V, Pd, Sn) [2–9] and mixed metal derivatives
AgMP MP (M ¼ Mg, Mn,
(M ¼ Sc, V, Cr, In, Bi) [10–14], Ag
Zn) [15–18], AgZnPS [19], Ag Ti 11 [20], AgTi [PS and
Ag NbTi 25 [21], ANb
PS10 (A ¼ Na, Ag) [22]. The ethane-like
] unit is the common building block in most of these
compounds. In the MPS or M families, the stability of the
3
(M ¼ Cd, Zn, Mn, Fe,
2
S
6
2
2 6
S
sphates Li
(A ¼ K, Cs) and K
homologue of V, the M
niobium is present as Nb in Nb
[45,46], which present different two-dimensional structural
patterns containing [Nb 12] units. The Nb atoms are centered
9
Nd
2
[PS
4
]
5
[41], K
2
NdP
[40] are observed. For the heavier
structural model is not observed and
PS10 [43], Nb 21 [44], NbP
2 7 9 4 4 3 4 2
S [42], K Nd[PS ] , A Nd[PS ]
4
2
2
P
2
S
2
4
]
3
P
6
S
2
3
Nd [PS
3
4 4
]
2
3
[
P
2
S
6
2 2 6
P S
4
+
P
2
S
2 8
S
3
2
P
2
S
6
2
4
transition metal in the 2+ oxidation state decreases from Zn to Ti.
Besides these divalent metals, trivalent metals were found to form
2
S
M
4
[P
deficient three-fold superstructure of the Fe
vanadium case, the most stable phase is a mixed valence phase
2
S
6
]
3
(M ¼ Cr, In, Ga) [23–25], which crystallize in a metal-
in distorted bicapped trigonal prismatic polyhedra, and neighbor-
ing polyhedra share square faces and edges forming Nb–Nb pairs.
The intercalation of alkali and silver into such structures breaks
the –S–S– or –S–S–S– bridges between the one-dimensional
2 2 6
P S
type. In the
3
V0.78PS [26]. The V(III), Cr(III) and In(III) compounds can be
chains to form ANb
PS10 [51], Rb0.38Ag0.5Nb
[53] and Rb Nb 11 [54]. Alkali and silver cations reside in
exactly the same site in the van der Waals gap between infinite
2
PS10 (A ¼ Na, Ag, K, Rb, Cs) [22,47–50],
K
0.5Ag0.5Nb
2
2
PS10 [52], K0.34Cu0.5Nb PS10
2
Ã
2 2
P S
Corresponding author. Fax: +49 4318801520.
2
E-mail address: wbensch@ac.uni-kiel.de (W. Bensch).
0
022-4596/$ - see front matter & 2008 Elsevier Inc. All rights reserved.
doi:10.1016/j.jssc.2008.11.017

ARTICLE IN PRESS
472
Y. Wu, W. Bensch / Journal of Solid State Chemistry 182 (2009) 471–478
chains. To stabilize the Nb(IV), we choose Ag(I) as counter-cation.
This choice was done according to the interesting specific
characteristics of Ag(I), e.g., abnormally high atomic displacement
parameters, a preference for low coordination environments and
with full matrix least squares techniques using the SHELXTL
software package [57].
2
.4.1. Ag
The structure was solved and refined successfully in space
group Pnma. The final cycle of refinement performed with 1923
2 2 6 2
Nb[P S ][S ]
10
10
tendency to form
d
–d
homo-atomic bonds when their
concentration is large [55]. Some detailed spectroscopic and
crystallographic investigations [3,56] have clearly demonstrated
2
unique reflections converged to residuals wR
and the conventional R index based on reflections F
2
(F
o
40) ¼ 0.0975
10
the unusually large atomic displacement parameters for d
2 2
o
o
42s (F )
cations derived from a static disorder produced by off-center
displacements.
was 0.0380. The resulting structural models of both compounds
were standardized using the program STRUCTURE TIDY [58] in
PLATON [59].
The aims of the present study were the syntheses and
characterization of new Ag(I) containing thiophosphates. The
results of the X-ray diffraction experiments should yield more
information about the behavior of Ag(I) in such thiophosphate
phases. In the manuscript we present the synthesis, structural
and optical characterization of new quaternary compounds
2 4
2.4.2. KAg [PS ]
The systematic absence conditions of the data set pointed to
eight possible space groups. The three choices with the lowest
CFOM (combined figure of merit) were I 4¯ (acentric), I 4¯ 2m
2 2 6 2 2 4
Ag Nb[P S ][S ] and KAg [PS ].
(
acentric) and I4/m (centrosymmetric). The intensity statistics
indicated a non-centrosymmetric space group. Therefore, we first
¯2m since it belongs to the higher symmetric
2.
Experimental
proceeded with I4
Laue class (4/mmm). All atoms were found with two runs of least-
squares/difference Fourier cycles. In the initial stages of the
refinement, the incorrect enantiomorphs (wrong absolute struc-
ture) were selected; therefore the coordinates were inverted with
the instruction MOVE 1 1 1 ꢀ1 and subsequently refined
anisotropically. After introducing an extinction coefficient, the R
values dropped significantly to R1 ¼ 0.0336 and wR2 ¼ 0.0893.
The absolute structure was determined and is in agreement with
the selected setting (Flack x parameter: ꢀ0.1(1)). The structure is
clearly non-centrosymmetric with no additional mirror planes
perpendicular to the c-axis and could not be solved in the
centrosymmetric space group I4/m. An attempt to solve the
structure in the non-centrosymmetric space group I 4¯ showed
2
.1. Reagents
The following reagents were used as purchased: K (99.5%,
Strem), Nb (99.97%, Fluka), P (99.99% purity, Alfa), S (99.99%,
Heraeus), Ag (99.99%, Degussa), Nd (99.99%, Alfa Aesar).
2 5
S
2.2. Synthesis
K
2
S
3
was prepared from a stoichiometric mixture of the
elements in liquid ammonia under an argon atmosphere.
2
.2.1. Preparation of Ag
Ag Nb[P ][S ] (1) was prepared by the reaction of a mixture
of 0.0664 g (0.62 mmol) of Ag, 0.0572 g (0.62 mmol) of Nb,
.1369 g (0.62 mmol) of P and 0.0395 g (1.23 mmol) of S. The
mixture was loaded in a fused silica tube which was then flame-
2 2 6 2
Nb[P S ][S ](1)
reasonable results. But a symmetry check with PLATON [59]
2
2
S
6
2
suggests the higher symmetry space group I42m.
¯
The parameters for data collection and the details of the
structural refinements for the two compounds are summarized in
Table 1. Atomic coordinates and isotropic displacement para-
meters are given in Table 2. Selected bond distances and angles
are listed in Tables 3 (1) and 4 (2).
0
2 5
S
ꢀ
3
sealed under vacuum (ꢁ10 mbar). The mixture was annealed at
00 1C for 6 days, followed by cooling to 100 1C at a rate of 2 1C/h.
The product contained red crystals (60% yield based on Nb).
5
2
.2.2. Preparation of KAg
(0.093 g, 0.53 mmol), Ag (0.058 g, 0.53 mmol), Nd (0.039 g,
.27 mmol), P (0.059 g, 0.27 mmol), S (0.051 g, 1.60 mmol) were
-filled glove-box and loaded into fused
2 4
[PS ] (2)
Table 1
K
2
S
3
Crystal data and selected refinement results for Ag Nb[P S ][S ] (1) and
2
2
6
2
0
2
S
5
2 4
KAg [PS ] (2).
thoroughly mixed in a N
2
ꢀ3
Ag
2
Nb[P
2
S
6
][S
2
]
2 4
KAg [PS ]
silica tube which was evacuated (1 ꢂ10 mbar) and flame-sealed.
The tube was placed in a computer controlled furnace and heated
to 700 1C within 24 h. After 5 days the sample was cooled down to
fw
627.15
414.05
Space group
˚
a (A)
Pnma
I 4¯ 2m
100 1C at a rate of 3 1C/h followed by cooling to room temperature
12.2188 (11)
26.3725 (16)
6.7517 (4)
2572.7 (3)
8
6.6471 (7)
6.6471 (7)
8.1693 (11)
360.95(7)
2
b ( A˚ )
c ( A˚ )
in 4 h. Excess flux was removed by washing the reaction product
with dimethylformamide (DMF) and acetone. The product con-
V (A˚
3
)
tained transparent colorless platelets K
light yellow platelets KAg [PS
] (ꢁ40%). A synthesis of KAg
was successful reacting stoichiometric amounts of K /Ag/P
00 1C. The product is stable in air for several weeks.
3
Nd[PS
4
]
2
(ꢁ40%) [40] and
[PS
at
Z
2
4
2
4
]
T (K)
170
293
ꢀ3
D
calc (g cm
)
3.829
3.810
2
S
3
2 5
S
ꢀ
1
m
(mm
)
6.371
7.263
7
Index range
ꢀ13php14
ꢀ8php8
ꢀ8pkp8
ꢀ10plp10
56
ꢀ
31pkp31
2.4. X-ray crystallography
ꢀ7plp7
55
2Y
max (1)
R
int
0.0446
0.0380
0.0975
0.983
0.0436
Data sets of selected crystals of both compounds were
R1(F
o
44
s
(F
o
))
0.0336
collected on a STOE imaging plate diffraction system (IPDS-1)
˚
wR2 (all data)
0.0893
with graphite monochromatized MoK
a
radiation (
l
¼ 0.7107 A) at
GOOF
1.196
[e A˚
ꢀ
3
]
1.965/ꢀ1.932
1.257/ꢀ1.166
D
r
room temperature for 1 and at ꢀ100 1C for 2. Size of crystal 1:
3
3
0
.13 ꢂ 0.09 ꢂ 0.07 mm ; crystal 2: 0.12 ꢂ 0.10 ꢂ 0.07 mm . The raw
P
P
R1 ¼ ||F
o
|ꢀ|F
c
||/ |F
o
|.
P
P
intensities were corrected for Lorentz, polarization and absorp-
tion. The structures were solved with direct methods and refined
2
o
2 2
2 2 1/2
o
2
o
2
2
o
wR2 ¼ [ w(F
ꢀF
c
) / w(F
) ] , w ¼ 1/[
s(F
)+(a*P) +b*P], where P ¼ (max(F
,0)+
2
c
2F )/3.

ARTICLE IN PRESS
Y. Wu, W. Bensch / Journal of Solid State Chemistry 182 (2009) 471–478
473
Table 2
Atomic coordinates and equivalent displacement parameters Ueq ( A˚ ꢂ10 ).
Table 3
´
2
3
Selected distances ( A˚ ) and angles (deg) for Ag
2 2 6 2
Nb[P S ][S ] (1).
x
y
z
U
eq
Ag(1)–S(2)
2.4771(19)
2.6185(19)
2.6305(19)
2.671(2)
Ag(1)–S(5)
Ag(2)–S(3)
Ag(2)–S(5)
2.491(2)
Ag(1)–S(6)
2.6077(18)
2.667(2)
Ag
2
Nb[P
2
S
6
][S
2
]
Ag(2)–S(2)
Ag(1)
Ag(2)
Nb(1)
P(1)
P(2)
S(1)
0.08482(7)
0.14926(6)
0.36746(5)
0.10680(15)
0.34241(15)
0.00499(14)
0.03093(15)
0.24340(14)
0.24167(14)
0.26540(15)
0.48122(14)
0.0351(2)
0.05458(3)
0.04371(3)
0.19556(2)
0.60636(7)
0.10707(7)
0.66453(6)
0.53747(7)
0.62128(7)
0.16593(7)
0.03929(7)
0.12282(6)
1
0.01326(12)
0.50780(10)
0.46668(9)
0.3074(3)
0.1257(3)
0.2510(3)
0.2804(3)
0.1479(3)
0.1764(3)
0.1737(3)
0.2765(3)
0.0604(4)
36(1)
24(1)
4(1)
5(1)
5(1)
7(1)
9(1)
7(1)
7(1)
10(1)
8(1)
9(1)
Ag(2)–S(5)
Nb(1)–S(10)
Nb(1)–S(7)
Nb(1)–S(1)
Nb(1)–S(3)
Nb(1)–Nb(1)
P(1)–S(3)
2.483(2)
Nb(1)–S(9)
2.491(2)
2.508(2)
Nb(1)–S(8)
2.508(2)
2.6044(18)
2.6776(18)
2.8714(13)
2.025(3)
Nb(1)–S(4)
2.6104(18)
2.6947(18)
2.011(3)
Nb(1)–S(6)
P(1)–S(1)
S(2)
P(1)–S(2)
2.048(3)
2.010(2)
P(1)–P(2)
2.237(3)
S(3)
P(2)–S(4)
P(2)–S(6)
2.021(3)
S(4)
P(2)–S(5)
2.046(3)
2.016(4)
P(2)–P(1)
2.237(3)
S(5)
S(8)–S(9)
S(10)–S(7)
2.023(4)
S(6)
S(2)–Ag(1)–S(5)
S(5)–Ag(1)–S(6)
S(3)–Ag(2)–S(5)
S(3)–Ag(2)–S(5)
S(5)–Ag(2)–S(5)
S(10)–Nb(1)–S(7)
S(10)–Nb(1)–S(8)
S(7)–Nb(1)–S(8)
S(9)–Nb(1)–S(1)
S(8)–Nb(1)–S(1)
S(9)–Nb(1)–S(4)
S(8)–Nb(1)–S(4)
S(10)–Nb(1)–S(3)
S(7)–Nb(1)–S(3)
S(1)–Nb(1)–S(3)
S(10)–Nb(1)–S(6)
S(7)–Nb(1)–S(6)
S(1)–Nb(1)–S(6)
S(3)–Nb(1)–S(6)
S(9)–Nb(1)–Nb(1)
S(8)–Nb(1)–Nb(1)
S(4)–Nb(1)–Nb(1)
S(6)–Nb(1)–Nb(1)
S(1)–P(1)–S(3)
S(3)–P(1)–S(2)
S(3)–P(1)–P(2)
S(4)–P(2)–S(6)
S(6)–P(2)–S(5)
S(6)–P(2)–P(1)
145.53(7)
107.68(6)
94.21(6)
S(2)–Ag(1)–S(6)
S(3)–Ag(2)–S(2)
S(2)–Ag(2)–S(5)
S(2)–Ag(2)–S(5)
S(10)–Nb(1)–S(9)
S(9)–Nb(1)–S(7)
S(9)–Nb(1)–S(8)
S(10)–Nb(1)–S(1)
S(7)–Nb(1)–S(1)
S(10)–Nb(1)–S(4)
S(7)–Nb(1)–S(4)
S(1)–Nb(1)–S(4)
S(9)–Nb(1)–S(3)
S(8)–Nb(1)–S(3)
S(4)–Nb(1)–S(3)
S(9)–Nb(1)–S(6)
S(8)–Nb(1)–S(6)
S(4)–Nb(1)–S(6)
S(10)–Nb(1)–Nb(1)
S(7)–Nb(1)–Nb(1)
S(1)–Nb(1)–Nb(1)
S(3)–Nb(1)–Nb(1)
S(1)–P(1)–S(3)
106.45(6)
105.83(6)
154.45(6)
92.72(6)
S(7)
4
1
S(8)
S(9)
S(10)
0.2002(2)
0.2977(2)
0.4388(2)
0.4996(5)
0.7404(4)
0.1957(4)
8(1)
8(1)
9(1)
107.12(6)
96.38(4)
47.83(8)
4
1
109.48(5)
90.20(7)
4
1
91.17(7)
47.58(8)
110.14(5)
80.73(7)
120.96(7)
75.22(7)
4
127.04(7)
121.89(7)
75.99(7)
159.58(7)
149.92(7)
74.70(5)
80.02(7)
KAg
Ag
2
[PS
4
]
126.69(8)
144.26(6)
84.81(6)
0
0
1
1
35(1)
18(1)
4
0
4
1
K
88.05(6)
2
0
79.99(6)
P
S
0
0
8(1)
83.07(5)
160.13(7)
150.49(7)
74.50(6)
0.18131(18)
0.18131(18)
0.1398(2)
15(1)
87.22(6)
79.56(6)
87.59(6)
54.80(4)
Estimated deviations are given in parentheses. The Ueq is defined as one third of
the trace of the orthogonalized Uij tensor.
54.68(4)
55.07(4)
55.08(4)
108.31(4)
137.02(4)
105.12(11)
112.33(11)
110.32(11)
102.61(10)
111.47(11)
109.87(10)
105.83(10)
107.42(4)
135.39(4)
105.12(11)
119.88(11)
106.29(10)
105.62(11)
119.05(11)
104.64(10)
S(1)–P(1)–S(2)
Further details of the crystal structure investigation can be
ordered referring to the no. CSD-420032 (Ag
20033 (KAg [PS ]), the authors and the citation of this paper at
the Fachinformationszentrum Karlsruhe, Gesellschaft f u¨ r wis-
senschaftlich-technische Information mbH. D-76344 Eggenstein-
Leopoldshafen (Germany). E-mail: crysdata@fiz-karlsruhe.de
S(1)–P(1)–P(2)
2 2 6 2
Nb[P S ][S ]), CSD-
S(2)–P(1)–P(2)
4
3
4
S(4)–P(2)–S(5)
S(4)–P(2)–P(1)
S(5)–P(2)–P(1)
2
2
.5. Physical measurements
.5.1. Infrared spectroscopy
Table 4
Selected distances ( A˚ ) and angles (deg) for KAg
2 4
[PS ] (2).
ꢀ1
ꢀ1
Infrared spectra in the MIR region (4000–400 cm , 2 cm
Ag–S
2.5980(7) ꢂ 4
3.2062(18) ꢂ 4
96.89(2) ꢂ 4
P–S
K–S
2:0519ð16Þ ꢂ 4
3.4003(18) ꢂ 4
139.47(7) ꢂ 2
108.06(5) ꢂ 4
129.53(6)
K–S
resolution) were recorded on a Genesis FT-spectrometer (ATI
Mattson). The samples were ground with dry KBr into fine
powders and pressed into transparent pellets. Infrared spectra in
the far-IR region (550–80 cm ) were collected on an ISF-66
device (Bruker) with the samples pressed in polyethylene pellets.
S–Ag–S
S–P–S
P–S–Ag
S–Ag–S
S–P–S
112.34(10) ꢂ 2
113.53(3) ꢂ 2
Ag–S–Ag
ꢀ
1
2
.5.2. Raman spectroscopy
are attached to the Ulbricht sphere. The samples were ground
with BaSO (as standard for 100% reflectance) and prepared as a
Raman spectra were recorded on an ISF-66 spectrometer
4
(
Bruker) equipped with an additional FRA 106 Raman module.
flat specimen. The resolution was 1 nm for the UV/vis range and
2 nm for the NIR range. The measuring range was 250–2000 nm.
An Nd/YAG laser was used as source (
l
¼ 1064 nm). The samples
were ground and prepared on Al sample holders. The measuring
range was ꢀ1000–3500 cmꢀ (resolution: 2 cm ).
Absorption (
using the Kubelka–Munk function [60]:
is the reflectance at a given wave-number,
a/S) data were calculated from the reflectance spectra
1
ꢀ1
2
a
/S ¼ (1ꢀR) /2R, where R
a
is the absorption
coefficient and S is the scattering coefficient. The band gap was
2
.5.3. Solid-state ultraviolet (UV)–visible (vis)–near-IR (NIR)
spectroscopy
Optical diffuse reflectance measurements were performed at
determined as the intersection point between the energy axis at
the absorption offset and the line extrapolated from the linear
2
part of the absorption edge in a (
a
/S) vs. E (eV) plot.
room temperature using a UV–vis–NIR two-channel spectrometer
Cary 5 from Varian Techtron Pty., Darmstadt. The spectrometer is
equipped with an Ulbricht sphere (Diffuse reflectance accessory;
Varian Techtron Pty.). The inner wall of the Ulbricht sphere
2.5.4. Microprobe analyses
Microprobe analyses were performed with a Philips ESEM XL
30 scanning electron microscope equipped with an EDAX
analyzer. The compositions are the result of averaging a large
(diameter 110 mm) is covered with a PTFE layer of 4 mm
thickness. A PbS detector (NIR) and a photomultiplier (UV/vis)

ARTICLE IN PRESS
474
Y. Wu, W. Bensch / Journal of Solid State Chemistry 182 (2009) 471–478
number of independent measurements from a given sample. The
EDX data yielded an atomic ratio of 1.7:1:1.8:7.6 (Ag:Nb:P:S) for
compound 1 and 1:2:1:3.7 (K:Ag:P:S) for compound 2.
units are grafted alternatively on both sides of these slabs. In the
[Nb 12] unit, both Nb atoms are surrounded by eight S atoms in a
distorted bicapped trigonal prismatic fashion as shown in Fig. 3.
Two adjacent NbS trigonal prisms share a rectangular face of two
pairs; the two other rectangular faces are capped by S atoms
2
S
8
2
2
ꢀ
S
4
ꢀ
3
3
3
.
Results and discussion
from [P S ] anions. The S–S bonds of the [S ] groups, 2.016(4)
2
6
2
2
ꢀ
˚
and 2.023(4) A, are characteristic for S
slightly off-centered, displaced towards the S
away from the [Ag anions. Indeed, the
˚
shortest Nb–S bonds (Nb–S(7, 8, 9, 10): 2.483(2)–2.508(2) A) are to
2
anions. The Nb atoms are
2
ꢀ
.1. Syntheses and crystal structures
2
anions and moved
4
ꢀ
2
S
4
] chains and [P
2
S
6
]
.1.1. Ag
2
Nb[P
2
S
6
][S
2
] (1)
2
ꢀ
A view of the structure of compound 1 is presented in Fig. 1.
the S atoms of the S
2
pairs. The Nb–S bonds involving S atoms
The structure is characterized by a strongly anisotropic three-
dimensional framework composed of three types of slabs. The
framework can be conveniently described as an assembly of
having bonds to both Ag and P atoms are the longest (Nb–S(3, 6):
˚
2.6776(18), 2.8714(18) A), whereas those to S atoms which are
only bound to P atoms are in-between (Nb–S(1, 4): 2.6044(18);
˚
˚
[
Nb
2
S12] units running along the [010] direction, ethane-like
2.6104(18) A). However, the average Nb–S distance of 2.572(2) A
˚
2
compares well with the value of 2.550(2) A in NaNb PS10 [22,47].
[
P
2
S
6
] groups and novel [Ag ] chains. The [Nb 12] units are not
2
S
4
2
S
4
ꢀ
IV
1
directly joined, but they are connected via the [P
2
S
6
]
anions
The presence of Nb 4d leads to a short Nb–Nb distance of
˚
along [001] to form intricate chains which contain 14-membered
2.8714(13) A, being comparable to those in NbP
2
S
8
[45,46],
rings (Fig. 2). Neighboring chains are linked through [Ag
˚
2
S
4
]
ANb
2
PS10 (A ¼ Na, Ag, K, Rb, Cs) [22,47–50], K0.5Ag0.5Nb
2
PS10
chains creating tunnels (diameter: 3.6 ꢂ10.3 A) along [001],
[51], Rb0.38Ag Nb PS
0.5
2
10
[52] and K Cu Nb PS
0.34
0.5
2
10
[53]. The
whereas [P
2
S
6
] units and [Ag
˚
2
S
4
] chains form tunnels with
tetracapped trigonal [Nb
with [P S ] entities to build alternating chains parallel to [001]
2
S12] biprisms share four opposite edges
dimensions of 3.6 ꢂ 6.5 A in-between. The latter tunnels are
2
6
compact and define uniform slabs of almost constant thickness,
(Figs. 1 and 2).
The [Nb 12] unit is a central structural motif in 2D-NbP
46], 3D-NbP [45], Nb PS10 [43] and Nb 21 [44]. The
formation of this building block may be mainly due to the
which constitute the central part of the framework. The [Nb
2
S
12
]
2
S
2 8
S
[
2
S
8
2
4 2
P S
1
IV
stabilization of the 4d electronic configuration of Nb by a D3h
IV
1
2
symmetry crystal field, as for V 3d in V PS10 [61]. On the other
2
2
ꢀ
IV
hand the presence of S
can come in close contact. In all reported [Nb
Nb–Nb distances are very similar independent of the number of S
pairs present in the actual structure: two [46] or four [43,44,48].
This distance is almost unchanged in isotypic [Nb 12] groups like
dumb-bells allows that the Nb centers
2
S12] units, the
2
2
X
Fig. 1. Perspective view of Ag
2
Nb[P
2
S
6
][S
2
] (1) along [001].
2
Fig. 3. A side view of tetracapped trigonal biprisms [Nb S12] with atomic labeling.
2
nꢀ
chain.
Fig. 2. Perspective view of a single [NbP
2
S
8
]

ARTICLE IN PRESS
Y. Wu, W. Bensch / Journal of Solid State Chemistry 182 (2009) 471–478
475
2 4
Fig. 4. View of the [Ag S ] chain along [001]. Displacement ellipsoids are drawn at the 50% probability level.
˚
˚
˚
in NbS
2
Cl12 (2.871(4) A) [62,63] or Nb
2
Se
9
(2.895(2) A) [64]. Like
bond length is 2.59 A comparable with that found in KAg
2
PS
4
in the other compounds mentioned above, the neighbored Nb
atoms form an isolated pair via a single Nb–Nb bond.
(see below).
Within the chain short and long Ag–Ag separations of
3.4425(11) and 3.5141(11) A alternate. With the usual oxidation
states for Ag, Nb and P and taking into account the S
straightforward charge balance (Ag
is achieved.
4
ꢀ
˚
The ethane-like [P
the second basic building block of the structure and is composed
of two [PS ] units sharing the vertex with each other to form a P–P
bond of 2.237(3) A. The P–S bond lengths range from 2.011(3) to
2
S
6
]
anion in staggered conformation is
2
2
ꢀ
anion, a
+
1
+4
+4
ꢀ2
2ꢀ
3
)
2
(Nb )(P
)
2
(S
) (S )
6
2
˚
˚
˚
2
.048(3) A (average: 2.027(3) A) being in good agreement with
Obviously, the structure of compound 1 is completely different
from that of AgNb PS10 [22,47] and K0.5
PS10 (M ¼ Cu, Ag)
[51,53]. In AgNb PS10 and K0.5Ag0.5Nb PS10, the [Nb 12] groups
dumbbells to form
anions bridge the Nb–Nb pair
data reported for M
2
P
2
S
6
(M ¼ Cd, Zn, Mn, Fe, Co, Ni, Hg, Mg, Ca, V,
2
M0.5Nb
2
Pd, Sn) [2–9]. However, a thorough analysis of the P–S bond
lengths and the S–P–S angles reveals that the P(1,2) atoms are
slightly displaced from the centres of the tetrahedra yielding three
groups of P–S bond lengths: (i) the P(1)–S(1) and P(2)–S(4) bonds
2
2
2
S
are connected via [PS
4
]
units and
S
2
1
1
ꢀ
3ꢀ
½Nb
2
PS10
ꢃ
chains. The [PS
4
]
+
with the long separation. Ag is in a distorted tetrahedral
˚
˚
of 2.011(3) and 2.010(2) A where the S atoms have bonds to a Nb
environment with two short Ag–S (2.545(4), 2.624(3) A) and two
˚
atom; (ii) the P(1)–S(3) and P(2)–S(6) bonds of 2.025(3) and
long bonds (2.872(4), 2.898(3) A). This Ag–S bonding pattern is
similar to that in the AgS tetrahedra in both title compounds.
Attempts to prepare the analogous Cu compound yielded
NbP [45,46]. This observation suggests that the ionic radius of
Cu is too small to stabilize the three-dimensional framework of 1.
˚
2
.021(3) A with S atoms being involved in bonds to Nb and Ag
4
atoms; (iii) the P(1)–S(2) and P(2)–S(5) bonds of 2.048(3) and
+
˚
2
.046(3) A with S atoms having also bonds to Ag ions. The S–P–S
2 8
S
angles indicate an obvious deviation from the tetrahedral
geometry (see Table 3).
The new puckered [Ag
block and is formed by Ag(1)S
Each Ag(1)S triangle shares the S(2) atom with one Ag(2)S
tetrahedron and the S(5) atom with two other Ag(2)S tetrahedra,
while each Ag(2)S tetrahedron shares two S(5) atoms with
neighboring Ag(1)S triangles and Ag(2)S tetrahedra and
the S(2) atom with one Ag(1)S triangle. The remaining S(3) and
S(6) atoms have bonds to Nb and P(2). Two Ag(1)S triangles
and two Ag(2)S tetrahedra are connected to form one
2
S
4
] chain (Fig. 4) is the third building
3
triangles and Ag(2)S tetrahedra.
4
2 4
3.1.2. KAg [PS ] (2)
3
4
Initially the syntheses were performed with the aim to prepare
new lanthanide (Nd) alkali-metal silver thiophosphates via the
flux method. Compound 2 was obtained in a reasonable yield
4
4
3
4
by reacting a mixture of K
2/2/1/1/6. Decreasing the amount of Ag leads to the formation of
Nd[PS as main product. The reaction without Nd was also
2 3 2 5
S /Ag/Nd/P S /S with molar ratio of
3
3
K
3
4 3
]
4
explored, and under the same conditions, compound 2 could
be obtained.
The structure is composed of a three-dimensional anionic
framework with orthogonal, intersecting tunnels hosting the K
six-membered ring. The chains containing six-membered rings
+
run along the [001] direction. Both Ag ions are ordered in
+
contrast to the disorder observed in Ag
2
NbTi
2
P
6
S25 [21].
The Ag(1)S triangle is slightly distorted with Ag(1)–S(2, 5, 6)
3
cations. These tunnels run parallel to the [100] and [010]
directions. In the asymmetric unit there are one K and P atom,
both located on 4¯ 2m sites, one Ag atom on 4¯ and an S atom on a
˚
bonds at 2.4771(19), 2.491(2), 2.6185(18) A and S–Ag–S angles
between 106.45(6) and 145.53(7)1. Ag(2) is in a strong distorted
tetrahedral coordination with Ag(2)–S bond lengths ranging from
mirror plane. The anionic framework is constructed by corner-
˚
2
9
.6077(18) to 2.671(2) A and corresponding angles between
sharing of alternating [PS
flattened eight-membered ring (Fig. 5). The [PS
4
] and [AgS
4
] tetrahedra, forming a
] tetrahedron is
regular, with all bonds at 2.519(16) A and bond angles between
108.06(5) and 112.34(10)1. The [AgS ] tetrahedron is severely
distorted with bond angles from 96.89(2) to 139.47(7)1, even
2.72(6)1 and 154.45(6)1.
Analyzing the anisotropic displacement parameters (ADP) it is
4
˚
obvious that Ag(1) exhibits the largest values for the ADP. Despite
that S(2) and S(5) serve as bridges within the chain and the
Ag(1)–S(2, 5) bonds are shorter than all Ag(2)–S bonds, the ADPs
of Ag(1) are larger. A possible explanation is the environment of
Ag(1) in the center of a plane made by three S atoms that allows
an unconstrained vibration perpendicular to the triangle.
4
˚
though all Ag–S bond lengths are 2.5980(7) A. The orthogonal
rings, perpendicular to the [100] and [010] directions, are
connected through P and S atoms to form a three-dimensional
body-centered framework. Every S atom is three coordinated to
one P and two Ag atoms. The structure can also be described as
+
The bridging S(2) atom connects two Ag ions with an Ag–S–Ag
angle of 86.89(6)1, whereas S(5) links three Ag with Ag–S–Ag
+
layers of corner-sharing [AgS
4
] tetrahedra combined to eight-
angles ranging from 83.65(6)1 to 126.74(7)1. The average Ag–S
membered rings parallel to the (001) plane. These layers are

ARTICLE IN PRESS
476
Y. Wu, W. Bensch / Journal of Solid State Chemistry 182 (2009) 471–478
stitched by [PS
three-dimensional framework. The tunnels accommodate the K
cations, which are coordinated by eight S atoms in a compressed
4
] tetrahedra along the [001] direction to form the
cationic radii in these compounds are very similar, they can be
viewed as relatively ideal derivatives of the chalcopyrite struc-
ture-type. Larger 2-c/a values are found for compound 2 (0.77),
+
˚
cube, with K–S distances from 3.2062(18) to 3.4003(18) A
KAg
2
AsS
4
2 4 4 2 4
(0.78) [65], KAg SbS (0.78) [66], (NH )Ag AsS (0.78)
˚
(
Table 4). The dimension of the tunnels is about 4.08 ꢂ 6.65 A
[67] and BaAg
2
GeS (0.83) [44]. The c-axis compression expands
4
measured from coordinate to coordinate.
the coordination number of one of the cations from 4 to 8. This is
the reason why these compounds containing non-tetrahedral
cations can adopt this structure type. In fact, in all of these
We note that compound 2 is isostructural with KAg
2
AsS
[68]. The
structure of these compounds can be derived from the ZnS
sphalerite-type structure. The chalcopyrite structure-type (CuFeS
69]) in space group I 4¯ 2d is an ordered superstructure of ZnS with
4
[65],
2 4 4 2 4 2 4
KAg SbS [66], (NH )Ag AsS [67] and BaAg GeS
+
+
2+
4
compounds K , NH , Ba occupy the large cation site whose
2
coordinate number is 8 instead of 4. P, As, Ge occupy the regular
tetrahedral site, while the remaining highly distorted tetrahedral
site is occupied by the Ag cation.
[
+
the Zn atoms being replaced alternatively by Cu and Fe in a
regular fashion. It is also possible that one type of cation is
distributed over two different crystallographic sites whereas the
other cation being located on only one site. But in this case the
3.2. Optical properties
symmetry will be reduced to I 4¯ 2m. For example, in Cu
3 4
SbS [70],
two-thirds of Cu are located on one crystallographic site, while
one-third sits on another site; and Sb is on the third site. From
sphalerite to chalcopyrite, a small distortion along the c-axis,
known as a tetragonal compression, is observed. The reason is the
difference of the radii of two cations that make the unit cell height
slightly less than twice the base dimensions. The ratio c/a (better
The solid state diffuse reflectance UV/vis spectra of compounds
1 and 2 (Fig. 6) show steep absorption edges and the band gaps Eg
are estimated to 2.02 eV for 1 and 3.02 eV for 2. These data are in
agreement with the transparent colorless (2) and red color (1) of
the samples.
The MIR and Raman spectra for 1 are shown in Fig. 7. The
2ꢀ
2
-c/a) is a measure of the tetragonal distortion. The 2-c/a values
for CuFeS (0.03), AgGaS (0.14), AgGaSe2 (0.11), AgInS (0.05)
71], CuInSe (0) [72], Cu SbS (0) [70] are small or zero. Since the
2
spectroscopic relevant units are bridging S dumbbells between
4
ꢀ
2
2
2
2 6
Nb atoms and [P S ] anions with approximate D3d symmetry.
4
ꢀ
[
2
3
4
For [P S ]
the following modes can be expected: Gvib(D3d
)
2
6
¼
3A1g(R)+3E
g
(R)+A1u+2A2u(IR)+3E (IR), where the gerade species
u
are Raman active and ungerade species, except A1u, are infrared
active. On the basis of the assignment of the Raman bands for
hexathiodiphosphates [23,73,74], the modes observed for the title
ꢀ1
compound are assigned. The peaks above 150 cm in the Raman
spectrum correspond to the modes of the [P
whereas the peaks below 150 cm may be explained with the
modes with participation of metal ions. Compared to the spectra
4
ꢀ
2
S
6
]
anions,
ꢀ1
of hexathiodiphosphates [23,73,74] and Li
4
[P
2 6
S ] [75], the band at
ꢀ1
384 cm is assigned to the A1g mixed symmetric P–P and P–S
ꢀ
1
stretching modes, while the resonances in the 150–350 cm
4
ꢀ
region may be caused by the [P
2
S
6
]
deformation or bending
ꢀ
1
vibrations (S–P–S and S–P–P modes (E
in the Raman spectrum (438 cm
g
)). The mode at 431 cm
in the IR) is assigned to
ꢀ
1
an A2u vibrational mode. This peak is normally only IR active,
but due to the missing inversion center between two P atoms in
4
ꢀ
2
Ag Nb[P
2
S
6
][S
2
], the [P
2
S
6
]
unit does not have idealized D3d
symmetry. This allows the A2u peak to be observed in the
Raman spectrum.
ꢀ
1
2 2 2 4
Analogous to Nb (S ) Cl [76], the weak resonance at 542 cm
ꢀ
1
in the Raman spectrum and the peaks at 537 and 593 cm are
attributed to the S–S stretching vibration. The remaining signals
2 4
Fig. 5. Perspective view of the structure of KAg [PS ] viewed along [010].
ꢀ
1
at 632 and 569 cm in the IR spectrum and the peaks at 630, 616
Displacement ellipsoids are drawn at the 50% probability level for Ag, K and S
atoms, 80% for P atoms.
ꢀ
1
and 572 cm
may be caused by P–S stretching vibrations.
2 2 6 2 2 4
Fig. 6. Transformed reflectance spectra of Ag Nb[P S ][S ] (1) (left) and KAg [PS ] (2) (right).

ARTICLE IN PRESS
Y. Wu, W. Bensch / Journal of Solid State Chemistry 182 (2009) 471–478
477
2 2 6 2
Fig. 7. MIR and FT-Raman spectra of Ag Nb[P S ][S ] (1).
4
ꢀ
Both Raman and IR assignments for the [P
well with those reported for K Fe[P ] [77], KLa[P
Cr [P [23].
2
S
6
]
unit correspond
[9] W. Klingen, R. Ott, H. Hahn, Z. Anorg. Allg. Chem. 396 (1973) 271–278.
[
[
[
10] S. Lee, P. Colombet, G. Ouvrard, R. Brec, Inorg. Chem. 27 (1988) 1291–1294.
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12] P. Colombet, A. Leblanc, M. Danot, J. Rouxel, Nou. J. Chim. New J. Chem. 7
2
2
S
6
2 6
S
] [78] and
4
2 6 3
S ]
(1983) 333–338.
[13] Z. Ouili, A. Leblanc, P. Colombet, J. Solid State Chem. 66 (1987) 86–94.
4
.
Conclusions
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4 (2005) 5293–5303.
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47–264.
4
[
The two new compounds Ag
crystallize in two different three-dimensional frameworks. The
compressed chalcopyrite related structure adopted by KAg [PS
indicates that compounds containing large alkali ions which
prefer high coordination numbers can be accommodated in this
structure type. The flexibility of this structure type could be useful
in modifying the properties of the material. It is also imaginable to
predict other possible quaternary silver sulfides and selenides that
might adopt the same structure type. In Ag
framework is constructed by [Nb 12] units linked through [P
units and the new [Ag ] chains built up from distorted [AgS
triangles and [AgS ] tetrahedra. In KAg
distorted tetrahedral environment whereas in Ag
two different polyhedra are observed for Ag . The occurrence of
Ag–Ag bonds could be ruled out, whereas the rather usual feature
of coinage elements was observed i.e., large anisotropic displace-
2 2 6 2 2 4
Nb[P S ][S ] and KAg [PS ]
2
[
[
17] M. Evain, F. Boucher, R. Brec, Y. Mathey, J. Solid State Chem. 90 (1991) 8–16.
18] F. Boucher, M. Evain, R. Brec, Eur. J. Solid State Inorg. Chem. 28 (1991)
383–395.
2
4
]
[19] P. Toffoli, J.C. Rouland, P. Khodadad, N. Rodier, Acta Cryst. C 41 (1985)
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7–75.
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5–65.
6
[
6
5
2 2 6 2
Nb[P S ][S ], the
[
[
22] E.Y. Goh, S.J. Kim, D. Jung, J. Solid State Chem. 168 (2002) 119–125.
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(1999) 388–391.
2
S
2
S
6
]
]
2 4
S
3
+
[24] R. Diehl, C.D. Carpentier, Acta Cryst. B 34 (1978) 1097–1105.
4
2
PS
4
the Ag ion is in a
Nb[P ][S
[25] D.S. Kyriakos, A.N. Anagnostopoulos, P. Christidis, V. Gountsidou, J. Cryst.
2
2
S
6
2
]
Growth 76 (1986) 6–8.
[26] G. Ouvrard, R. Freour, R. Brec, J. Rouxel, Mater. Res. Bull. 20 (1985) 1053–1062.
+
[
[
[
27] G. Burr, E. Durand, M. Evain, R. Brec, J. Solid State Chem. 103 (1993) 514–518.
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ment parameters (ADP) especially for the AgS
ADPs are often a hint for Ag mobility and the investigation of
ionic conductivity will be done in the near future.
3
triangle in 1. Large
[30] V. Maisonneuve, C. Payen, V.B. Cajipe, J. Solid State Chem. 116 (1995) 208–210.
+
[
[
[
[
[
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18 (1995) 157–164.
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2
Acknowledgments
1401–1410.
Financial support by the State of Schleswig-Holstein, the Fonds
der Chemischen Industrie (FCI) and DFG (Deutsche Forschungs-
gemeinschaft) is gratefully acknowledged.
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[
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