Synthesis and Characterization of New Double
Tungstates Li
2
M
II
(WO
4
)
2
(M ) Co, Ni, and Cu)
M. A Ä lvarez-Vega,
†
J. Rodrı ´guez-Carvajal,
‡
J. G. Reyes-Ca ´ rdenas,
§
A. F. Fuentes,
|
and U. Amador*
,†
Departamento de Quı ´mica Inorga ´ nica y Materiales, Facultad de Ciencias Experimentales y
Te ´ cnicas, Universidad San Pablo-CEU, Urbanizacio ´ n Monteprı ´ncipe, 28668-Boadilla del
Monte, Madrid, Spain, Lab. Le ´ on Brillouin, CEA-CNRS, Centre d'Etudes de Saclay,
91191-Gif sur Yvette Cedex, France, Facultad de Ciencias Quı ´micas, U.A.N.L., San Nicola ´ s de
los Garza, Nuevo Leo ´ n, Me ´ xico, and CINVESTAV-IPN Unidad Saltillo, Carr.
Saltillo-Monterrey Km. 13, Apdo. Postal N. 663, 25000-Saltillo, Coahuila, Me ´ xico
Received February 13, 2001. Revised Manuscript Received June 25, 2001
Two new double tungstates, Li
2
Co(WO
4
)
2
and Li
2
Ni(WO
4
)
2
, have been prepared by solid-
state reaction and characterized. The structures of these isostructural compounds (triclinic,
space group P1 h ) have been determined from X-ray and neutron diffraction data and found
to be built up of alternating layers of zigzag rows of edge-sharing WO
6
octahedra and MO
6
octahedra (M ) Co
2+
or Ni
2+
) as in wolframite-like phases. However, the MO
6
octahedra are
arranged in columns but not connected to each other; perpendicular to these columns there
are rows of edge-sharing LiO
6
octahedra which also connect the different MO
6
octahedra.
The structure of a previously reported lithium-copper(II) double tungstate with the same
stoichiometry, Li
2
Cu(WO
4
)
2
, has also been determined and found to be similar to that
proposed for these new double tungstates. The three compounds melt incongruently at
temperatures between 750 and 770 °C. Conductivity measurements revealed that these
compounds are not good ionic conductors probably because of the full occupancy of lithium
positions which hinders the motion of the ions along the (LiO
6
)
∞
columns.
Introduction
A large number of double tungstates and molybdates
have been studied in recent years, basically because of
their interesting luminescence properties and possible
application in the field of solid-state lasers.
1-3
Many of
these double tungstates have the general formula A
I
M
III
-
(WO
4
)
2
, where A is an alkali metal and M is a trivalent
cation such as Bi
3+
, In
3+
, or Cr
3+
or a rare earth element
such as Sm
3+
, Eu
3+
, Gd
3+
, and so forth. As in the MWO
4
family of compounds, two different coordinations have
also been found for tungsten in these phases, either
tetrahedral for the scheelite-like double tungstates as
in NaLa(WO
4
)
2
4
or octahedral for those adopting the
wolframite type of structure as in LiFe(WO
4
)
2
.
5
How-
ever, only a few double tungstates of divalent elements
have been structurally investigated and not much has
been said about their chemical and/or physical proper-
ties. In fact, to our knowledge, only four elements (cop-
per, iron, magnesium, and zinc) have been found to form
this type of compound. Thus, Russian authors described
lithium double tungstates of Cu(II) and Fe(II), with the
general formula Li
2
M
II
(WO
4
)
2
(Li
2
O/MO/2WO
3
, 1:1:2).
6,7
Although the structures were not fully investigated at
the time, a wolframite-like structure was proposed for
both compounds. The wolframite ((Fe,Mn)WO
4
)-type
structure is very common among MWO
4
compounds
(where M
2+
is a 3d transition metal ion with a radius
smaller than 1 Å), and it can be described as made up
of hexagonal close-packed oxygens with certain octahe-
dral sites filled by M
2+
and W
6+
cations in an ordered
way.
8
Magnesium has been reported to form two double
tungstates though with different stoichiometry than
that proposed for Fe(II) and Cu(II): Li
2
Mg
2
(WO
4
)
3
(1:2:3)
9
and Na
4
Mg(WO
4
)
3
(2:1:3).
10
While no structural
data have been given for the sodium-magnesium
double tungstate, the crystal structure of Li
2
Mg
2
(WO
4
)
3
was considered to be similar to that of Li
2
Fe
2
(MoO
4
)
3
and Li
3
Fe(MoO
4
)
3
,
11
with W
6+
tetrahedrally coordinated
to four oxygen atoms. Finally, three double tungstates
of divalent zinc have been reported, though none with
lithium: Na
2.4
Zn
0.8
(WO
4
)
2
,
7
Na
4
Zn(WO
4
)
3
,
10
and K
4
Zn-
(WO
4
)
3
.
12
From these, structural data have been given
* Corresponding author. Telephone: 34 91 372 47 37. Fax: 34 91
351 04 75. E-mail: UAMADOR@CEU.ES.
†
Universidad San Pablo-CEU.
‡
Centre d’Etudes de Saclay.
§
U.A.N.L., San Nicola ´s de los Garza.
|
CINVESTAV-IPN Unidad Saltillo.
(1) Musset, O.; Boquillon, J. P. Appl. Phys. B: Lasers Opt. 1997,
65 (1), 13.
(2) Pujol, M. C.; Rico, M.; Zaldo, C.; Sole, R.; Nikolov, V.; Solans,
X.; Aguilo, M.; Diaz, F. Appl. Phys. B 1999, 68, 187.
(3) Faure, N.; Borel, C.; Couchand, M.; Basset, G.; Templier, R.;
Wyon, C.; Appl. Phys. B 1996, 63, 593.
(4) Byrappa, K.; Jain, A. J. Mater. Res. 1996, 11, 2869.
(5) Salmon, R.; Casalot, A.; Le Flem, G.; Hegenmuller, P. Mater.
Res Bull. 1970, 5, 341.
(6) Klevtsova, R. F.; Borisov, S. V. Kristallografiya 1969, 14, 610.
(7) Efremov, V. A.; Trunov, V. K. Russ. J. Inorg. Chem., 1974, 19,
272.
(8) Keeling, R. O. Acta Crystallogr. 1957, 10, 209.
(9) Fu, V.; Li, W. X. Powder Diffraction 1994, 9, 158.
(10) Smirnova, N.; Kislyakov, V. Inorg. Mater. (Engl. Transl.) 1971,
7, 1683.
(11) Klevtsova, R. F.; Magarill, S. A. Kristallografiya 1970, 15, 710.
3871 Chem. Mater. 2001, 13, 3871-3875
10.1021/cm010129n CCC: $20.00 © 2001 American Chemical Society
Published on Web 09/22/2001