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Ó 2004 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 77, 505–509 (2004)
505
Syntheses and Crystal Structures of New Quaternary Ag-Containing
Group 5 Chalcogenides: KAg2MVSe4 and K3Ag3MV S (MV = Nb, Ta)
2 8
ꢀ;1
Wen-Tong Chen,1;2 Hong-Wei Ma,1 Guo-Cong Guo, Lei Deng,1 Guo-Wei Zhou,1
Zhen-Chao Dong,3 and Jin-Shun Huang1
1State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of matter,
the Chinese Academy of Sciences, Fuzhou, Fujian 350002, P. R. China
2Graduate School, the Chinese Academy of Sciences, Beijing 100039, P. R. China
3National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047
Received July 23, 2003; E-mail: gcguo@ms.fjirsm.ac.cn
Four new quaternary Ag-containing group 5 chalcogenides, KAg2NbSe4 (1), KAg2TaSe4 (2), K3Ag3Nb2S8 (3), and
K3Ag3Ta2S8 (4), have been prepared through the use of molten alkali metal polychalcogenides as reactive fluxes and
structurally characterized by single-crystal X-ray diffraction techniques. The layer-type structures of 1 and 2 can be re-
garded as constructed from the basic building block of the incomplete cubane [Ag3MVSe3], which are corner-shared to
form an infinite chain along the a direction. These incomplete cubane chains are interconnected and further bridged by Se
atoms along the c direction, leading to a two-dimensional structure. The crystal structure of 3 and 4 consists of one-
dimensional triple-metal [Ag3MV2S8]3ꢁ anionic chains seperated by Kþ cations. The alternate packing of MVS4 and AgS4
tetrahedra via edge-sharing along the b direction leads to mixed-metal sub-chains, every two of which are further linked
by AgS4 tetrahedra along the a direction through edge-sharing to the MVS4 tetrahedra, thus yielding the so-called triple-
metal chains.
Metal chalcogenides are of long standing interest because of
their useful properties. In particular, group 5 chalcogenides
have been investigated extensively in regards to their supercon-
ductivity and charge density wave transition properties.1 Qua-
ternary group 5 chalcogenides A/MI/MV/Q (A = alkali metal;
MI = Cu, Ag; MV = V, Nb, Ta; Q = S, Se, Te) that have been
isolated and structurally characterized are mainly copper com-
pounds, e.g., A2CuMVQ4,2 ACu2MVQ4,3 K3Cu3MV2Q8 (MV =
Nb, Ta; Q = S, Se),4 K3CuNb2Se12,2b and Na8Cu4Nb2S21.5 In
contrast, the examples of silver analogues are limited, amount-
ing only to the A2MIMVQ4 structure type, such as A2AgVQ4,6
A2AgNbQ4,6b,7 and A2AgTaQ4.7b
The quaternary group 5 chalcogenides are now generally
prepared by the reactive flux method first described by Ibers.8
This technique has been well established as a new route for
the preparation of new compounds containing (poly)chalcoge-
nide species.9 Due to the propensity of copper atoms to assume
an oxidation state of I, copper was usually employed as a pseu-
doalkali metal to substitute for the Kþ ions in K3MVQ4 (MV =
V, Nb, Ta; Q = S, Se, Te).10,2d Because of the different coordi-
nation preference between Cu and K cations, the dimensional-
ity of the resulting compounds increases with the decrease in
alkali metal content.11 This trend has also been found in a
new series of metal chalcogenides K2MIMIII3Se6.12 The scarci-
ty of quaternary silver analogues stimulated our interests in the
metal chalcogenides.13
first silver compounds to form AMI2MVQ4 and A3MI3MV2Q8
type structures.
Experimental
Materials. All materials were of analytical grade and used as
received.
Syntheses. KAg2MSe4 (M = Nb (1), Ta (2)) were prepared
from the reaction of K2Se4 (0.394 g, 1 mmol), Nb (0.093 g, 1
mmol) or Ta (0.181 g, 1 mmol), Ag (0.108 g, 1 mmol), and Se
(0.395 g, 5 mmol). K2Se4 was made from the stoichiometric reac-
tion of elemental K and Se in liquid ammonia under a nitrogen at-
mosphere. The starting materials were loaded into a Pyrex tube that
was subsequently evacuated to 10ꢁ4 Torr and flame-sealed. The
tubes were placed in a programmable furnace, slowly heated from
room temperature to 450 ꢂC at a rate of 2 ꢂC/h, kept at 450 ꢂC for a
week, slowly cooled to 150 ꢂC at 4 ꢂC/h, and finally cooled to
room temperature over 4 h. The excess KxSey flux was removed
by washing with DMF to isolate orange prismatic crystals of
KAg2MSe4 in low yield (ca. 10% on Ag powder).
K3Ag3M2S8 (M = Nb (3), Ta (4)) compounds were synthesized
from a similar reaction of K2S4 (0.207 g, 1 mmol), powders of el-
emental Nb (0.093 g, 1 mmol) or Ta (0.181 g, 1 mmol), Ag (0.108
g, 1 mmol), and S (0.160 g, 5 mmol). K2S4 was made from the sto-
ichiometric reaction of elemental K with S in liquid ammonia un-
der a nitrogen atmosphere. The tubes were placed in a furnace that
was slowly heated from room temperature to 500 ꢂC over 24 h and
held there for a week, afterwards cooled to 475 ꢂC at 1 ꢂC/h, then
to 150 ꢂC at 4 ꢂC/h, and finally to room temperature over 4 h. The
excess KxSy flux was removed by washing with DMF to isolate
dark-brown prismatic crystals of K3Ag3M2S8 in low yield (ca.
10% on Ag powder).
In this paper we report the syntheses and structural character-
izations of new quaternary silver group 5 chalcogenides,
KAg2MVSe4 and K3Ag3MV2S8 (M = Nb, Ta), prepared by
the reactive flux technique, which, to our knowledge, are the
Published on the web March 12, 2004; DOI 10.1246/bcsj.77.505
Chen, Wen-Tong
