Phase formation in Cs2MoO4-MMoO4- Zr(MoO4)2 (M = Mn, Mg, Co, Zn) systems and crystal structure of new double molybdates Cs2 MnZr2 (MoO 4)6 and Cs2 MnZr(MoO4)4

Article abstract of DOI:10.1134/S0036023610050189

Subsolidus phase relations in the Cs₂MoO₄-MMoO ₄-Zr(MoO₄)₂ (M = Mn, Zn) ternary systems were determined, and two groups of new isostructural triple molybdates were synthesized: Cs₂MZr(MoO₄)₄ and Cs ₂MZr₂(MoO₄)₆ (M = Mn, Mg, Co, Zn). Cs₂MnZr₂(MoO₄)₆ and Cs ₂MnZr(MoO₄)₄ crystals were grown by spontaneous flux crystallization and used in structure solution for both groups of compounds. The Cs₂MnZr₂(MoO₄)₆ structure (a =13.4322(2) ?, c = 12.2016(3) ?, space group R3?, Z = 3, R = 0.0367) is a new structure type characterized by a mixed three-dimensional framework built of corner-sharing MoO₄ tetrahedra and (M, Zr)O₆ octahedra where large channels are occupied by cesium cations. Cs₂MnZr₂(MoO₄)₄ (a =5.3890(1) ?, c = 8.0685(3) ?, space group P3? m1, Z = 0.5, R = 0.0247) has the layered glaserite-like KAl(MoO₄)₂ type structure, where Al³⁺ octahedral positions are randomly occupied by a 0.5M²⁺ + 0.5Zr⁴⁺ mixture. Pleiades Publishing, Ltd., 2010.

Full text of DOI:10.1134/S0036023610050189

ISSN 0036ꢀ0236, Russian Journal of Inorganic Chemistry, 2010, Vol. 55, No. 5, pp. 771–779. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © G.D. Tsyrenova, S.F. Solodovnikov, N.N. Pavlova, Z.A. Solodovnikova, 2010, published in Zhurnal Neorganicheskoi Khimii, 2010, Vol. 55, No. 5, pp. 826–834.
PHYSICOCHEMICAL ANALYSIS
OF INORGANIC SYSTEMS
Phase Formation in Cs MoO –MMoO –Zr(MoO ) (M = Mn,
2
4
4
4 2
Mg, Co, Zn) Systems and Crystal Structure of New Double
Molybdates Cs MnZr (MoO ) and Cs MnZr(MoO )
2
2
4 6
2
4 4
a
b,c
a
b
G. D. Tsyrenova , S. F. Solodovnikov , N. N. Pavlova , and Z. A. Solodovnikova
a
Baikal Institute of Nature Management, Siberian Branch, Russian Academy of Sciences, UlanꢀUde, Buryat Republic, Russia
b
Nikolaev Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences,
pr. Akademika Lavrent’eva 3, Novosibirsk, 630090 Russia
c
Novosibirsk State University, Novosibirsk, Russia
eꢀmail: gtsyr@mail.ru
Received January 14, 2009
Abstract—Subsolidus phase relations in the Cs MoO –MMoO –Zr(MoO ) (M = Mn, Zn) ternary sysꢀ
2
4
4
4 2
tems were determined, and two groups of new isostructural triple molybdates were synthesized:
Cs MZr(MoO ) and Cs MZr (MoO ) (M = Mn, Mg, Co, Zn). Cs MnZr (MoO ) and
2
4 4
2
2
4 6
2
2
4 6
Cs MnZr(MoO ) crystals were grown by spontaneous flux crystallization and used in structure solution for
2
4 4
both groups of compounds. The Cs MnZr (MoO ) structure (
a
=13.4322(2) Å,
= 0.0367) is a new structure type characterized by a mixed threeꢀdimensional framework
built of cornerꢀsharing MoO tetrahedra and ( , Zr)O octahedra where large channels are occupied by
c = 12.2016(3) Å, space
2
2
4 6
group R⎯ 3, Z = 3, R
M
4
6
cesium cations. Cs MnZr (MoO ) (
a
=5.3890(1) Å,
c = 8.0685(3) Å, space group P3 m1, Z = 0.5, R =
2
2
4 4
0
.0247) has the layered glaseriteꢀlike KAl(MoO4)2 type structure, where Al3+ octahedral positions are ranꢀ
domly occupied by a 0.5M2+ + 0.5Zr4+ mixture.
DOI: 10.1134/S0036023610050189
Recent years have seen intense interest in ternary cesium carbonate, zirconium dioxide, oxides or carꢀ
molybdates, phosphates, and other complex oxide bonates of divalent metals (MgCO3, MnO, ZnO,
compounds containing tetravalent zirconium [1–5]. Co O4), and molybdenum trioxide (all of chemically
3
Many such compounds have found application, for pure grade). Cesium molybdate was prepared by stepꢀ
example, as luminescent and laser materials and solid wise annealing in the 200–650°С range and zirconium
electrolytes. A characteristic structural feature of these
compounds is a threeꢀdimensional mixed framework
built of cornerꢀsharing ZrO6 octahedra and Mo(P)O4
tetrahedra where voids are populated by monovalent
cations [2, 4, 5]. Moderateꢀsize divalent and trivalent
molybdate at 400–750°С for 80 h. Under these condiꢀ
tions the latter was isolated as the highꢀtemperature
phase. MMoO4 (M = Mn, Co, Zn, Mg) simple
molybdates were prepared using ceramic technology
[
6] by annealing equimolar mixtures of starting carꢀ
bonates and/or oxides of divalent metals for 100 h at
50–700°С. Xꢀray diffraction characteristics of the
4+
cations are most frequent partners of Zr in these
+
structures and relevant ternary systems; Rb is the
4
largest monovalent cation. Cesiumꢀcontaining ternary
molybdate systems with zirconium and compounds
formed in them yet remain poorly studied. This work
is concerned with subsolidus phase formation in the
Cs MoO –MMoO –Zr(MoO ) systems, where M =
cesium, zirconium, manganese, cobalt, zinc, and
magnesium molybdates synthesized as above agree with
those deposited with the ICDD PDFꢀ2 Database [7].
Subsolidus interactions in the Cs MoO –
2
4
4
4 2
2
4
Mn, Mg, Co, or Zn; relevelation and preparation of new MMoO –Zr(MoO ) ternary salt systems have been
4
4 2
zirconiumꢀcontaining triple molybdates; and soluꢀ studied in detail for M = Mn and Zn. Subsolidus phase
tion of Cs MnZr (MoO ) and Cs MnZr(MoO )
crystal structures.
relations in triangles were established using the interꢀ
secting joins method [8].
2
2
4 6
2
4 4
Powder Xꢀray diffraction analysis was carried out
on a D8 Advance (Bruker) diffractometer using
EXPERIMENTAL
Bragg–Brentano geometry (Cu
К
radiation,
2θ
=
α
The starting reagents used to synthesize cesium, 10°–70°, 0.02° scan steps). Unit cell parameters were
zirconium, and divalent metal molybdates were calculated by choosing isostructural analogues [9].
771

772
TSYRENOVA et al.
Nonius X8 Apex fourꢀcircle automated diffractometer
Mo , graphite monochromator, CCD area detecꢀ
MnMoO4
(а)
(
λ
K
α
tor,
ϕ
scans in 0.5° scan steps). Absorption correction
was applied by averaging over equivalent reflections.
All calculations in structure solution and refinement
were performed in the anisotropic approximation
using the SHELXꢀ97 program package [11].
1:2
RESULTS AND DISCUSSION
S1
Subsolidus Phase Relations in the Cs MoO –
2
4
MnMoO –Zr(MoO ) System
4
4 2
S2
To recognize whether new zirconiumꢀcontaining
molybdates can form, we studied the subsolidus region
of the Cs MoO –MnMoO –Zr(MoO ) system. This
2
4
4
4 2
work was preceded by the revision of data on the comꢀ
pounds existing in the relevant boundary binary sysꢀ
tems. In Cs MoO –MnMoO4, a single compound was
Cs MoO 4 : 1
4
1 : 1
Zr(MoO4)2
2
2
4
ZnMoO4
(b)
found, namely, Cs Mn (MoO ) having a langbeiniteꢀ
2 2 4 3
type structure. In Cs MoO –Zr(MoO ) , two inconꢀ
2
4
4 2
gruently melting double molybdates exist:
Cs Zr(MoO ) and Cs Zr(MoO4)3. The results we
8
4 6
2
obtained for the binary salt subsystems match those
reported in [12–14]. In our experiments we found that
the third boundary system MnMoO –Zr(MoO ) is of
3
: 5
4
4 2
the eutectic type.
1
: 1
The results of experiments on phase relations in the
Cs MoO –MnMoO –Zr(MoO ) ternary salt system
2
4
4
4 2
S1
are illustrated by Fig. 1a. A new phase of composition
Cs MnZr(MoO ) (S1 is found to exist on the
MnMoO –Cs Zr(MoO ) join. Xꢀray diffraction patꢀ
S2
2
4 4
)
4
2
4 3
terns for samples over the entire range of concentraꢀ
tions from MnMoO4 to Cs MnZr(MoO ) contain
2
4 4
reflections from MnMoO4 and Cs MnZr(MoO )
2
4 4
Cs MoO 4 : 1
2
1 : 1
Zr(MoO4)2
4
solely. Twoꢀphase quasibinary joins in the solidus
regions are as follows: S1 Cs Zr(MoO ) , S1
Cs Mn (MoO ) , Cs Zr(MoO ) –Cs Mn (MoO )
⎯
–
2
4 3
Fig. 1. Subsolidus phase relations in (a) Cs MoO –
,
2
4
2
2
4 3
2
4 3
2
2
4 3
MnMoO –Zr(MoO ) system (S1 = Cs MnZr(MoO ) ,
4
4 2
2 4 4
and Cs Mn (MoO ) –Cs Zr(MoO ) .
4 6
In the
2
2
4 3
8
S2
Zr(MoO4)2 system
Cs ZnZr (MoO ) ) at 500°C.
= Cs МnZr (MoO ) ) and (b) Cs MoO –ZnMoO –
2 2 4 6 2 4 4
Cs MnZr(MoO ) –Zr(MoO ) system, reflections
2
4 4
4 2
(
S1
=
Cs ZnZr(MoO ) , S2
=
2
4 4
from the S1 phase, Zr(MoO4)2, and another new triple
molybdate of composition Cs МnZr (MoO ) (S2
2
2
4 6
)
2
2
4 6
were detected in Xꢀray diffraction patterns of samples
Metrical characteristics were refined by least squares over the entire range of concentrations. Thus, quasiꢀ
using the CSD program package [10].
binary joins in the rightꢀhand part of the concentraꢀ
tion triangle are as follows: MnMoO –S2 S ,
,
S1
–
2
Thermoanalytical experiments were performed on
a Netzsch STA 449C thermal analyzer in the temperꢀ
ature range from 25 to 900°С (atmosphere: argon;
heating rate: 10 K/min).
4
Cs Zr(MoO ) –S2, and Zr(MoO ) –S2
.
2
4 3
4 2
Individual
Cs MnZr(MoO )
2
and
4 4
Cs МnZr (MoO ) were isolated as polycrystals as a
2
2
4 6
Crystals
of
4 6
new
triple
molybdates result of 200ꢀh stepwise annealing up to 550°C (for
4 4
grown by spontaneous flux crystallization using ing cesium, manganese, and zirconium molybdates of
cesium dimolybdate Cs Mo O as the solvent. Temꢀ appropriate stoichiometries.
S )
1
Cs MnZr (MoO ) and Cs MnZr(MoO ) were and 700°С (for S
2
) of the reaction mixtures comprisꢀ
2
2
2
2
2
7
perature was maintained with an accuracy of
using an RIFꢀ101 thermal regulator.
±
0.5 K
We failed to find a structure analogue for
Cs МnZr (MoO4)6; singleꢀcrystal data were necessary
2
2
Triple molybdate single crystals grown as described for revealing the structural features of this phase. Single
above were used in singleꢀcrystal Xꢀray diffraction crystals of the compound were grown from the batch of
experiments. Data were collected and unit cell paramꢀ composition 14.2 mol % Cs MoO4 + 28.6 mol %
2
eters were refined at room temperature on a Brukerꢀ MnMoO4 + 43 mol % Zr(MoO4)2 + 14.2 mol %
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 5 2010

PHASE FORMATION
Table 1. Xꢀray diffraction data and details of the Xꢀray diffraction experiment for Cs MnZr (MoO ) and Cs MnZr (MoO )
4 4
773
2
2
4 6
2
2
Compound
Cs MnZr (MoO )
Cs MnZr(MoO )
2 4 4
2
2
4 6
Crystal system
Trigonal
Trigonal
Space group
R
3
P3 m1
Unit cell parameters
a
, Å
13.4322(2)
12.2016(3)
5.8390(1)
8.0685(3)
c
, Å
V
, Å3/
, g/cm3
Z
1906.52(6)/3
3.822
238.232(11)/0.5
3.665
ρ
calc
μ
(MoK
), mm–1
7.034
7.549
α
Crystal color, shape, and size, mm3
Yellow chip
Light brown platelet
0
.08
×
0.06
×
0.04
0.12
2.52–29.98
2183/303 [ (int) = 0.0303]
298
×
0.12
×
0.02
Reflection angles θ, deg
2.42–37.72
Number of measured/unique reflections
8192/2165 [
R
(int) = 0.0191]
R
Number of reflections with
n
[I
> 2σ
(I
)]
2065
57
Number of refined parameters
Extinction factor
p
18
0.026(3)
1.330
0.0031(2)
1.304
GOOF = [
) for > 2
F2) for
> 2
for all reflections
Σ
w[F( F(
exp)2 – calc) ] /(n – p)]1/2
2 2
R
(
F
I
σ
(
I)
0.0367
0.0247
wR
(
I
σ
(
I)
0.0892
0.0556
R
(F
)
0.0475
0.0252
wR
(
F2
)
for all reflections
, e/Å3
0.1067
0.0558
ρmax/
ρ
6.039/–3.224
0.660/–1.639
min
Cs Mo O7; this composition was chosen by trial and Subsolidus Phase Relations in the Cs MoO –ZnMoO –
2
2
2
4
4
error. Spontaneous crystallization was carried out by
cooling a melted mixture from 740 to 710°С at a rate
of 10 K/h and then to 680°С at 15 K/h; the cooling
rate was then increased to 30 K/h and maintained till
Zr(MoO ) System
4 2
In the course of studying solidꢀphase interactions
between Cs MoO , ZnMoO4, and Zr(MoO4)2 over wide
2
4
ranges of temperatures and concentrations, we
obtained two new ternary phases of compositions
200°С, followed by furnace cooling. As a result, we
obtained yellow elongated prismatic crystals suitable
for Xꢀray crystallography.
Cs ZnZr(MoO ) (S1
) and Cs ZnZr (MoO ) (S2).
2
4 4
2 2 4 6
Single crystals of Cs MnZr (MoO ) triple molybꢀ
2
2
4 4
Table 2. Crystallographic characteristics of Cs MZr(MoO )
2
4 4
date were prepared for the first time by flux crystallizaꢀ
tion from the batch of composition 30.77 mol %
Cs MoO + 30.77 mol % MnMoO4 + 30.76 mol %
and Cs MZr (MoO ) (M = Mg, Co, Zn)
2
2
4 6
Unit cell parameters, Å
2
4
, Å3
V
Compound
Zr(MoO4) + 7.7 mol % Cs Mo O upon cooling from
2
2
2
7
a
c
6
80°С at a rate of 4 K/h, and Xꢀray structure analysis
was carried out. This compound crystallizes in the
KAl(MoO4)2 type structure [15] characteristic for Cs
Cs MgZr(MoO )
5.810(1)
5.809(1)
5.806(1)
8.065(3)
8.044(1)
8.048(1)
235.77
235.08
234.99
2
4 4
CoZr(MoO )
4 4
2
crystals exhibiting ferroelastic properties [16, 17].
Cs ZnZr(MoO )
2 4 4
Cs CoZr (MoO ) 13.3420(2) 12.1871(3) 1878.77(6)
Crystal data for cesium manganese zirconium
molybdates are compiled in Table 1.
2
2
4 6
Cs ZnZr (MoO ) 13.366(1) 12.253(3) 1895.6(5)
2
2
4 6
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 5 2010

774
TSYRENOVA et al.
Cs MoO –ZnMoO binary subsystem [18–20] and
(
а)
DSC,
μ
V/mg
Exo
2
4
4
TG, %
trace the evolution of the triangulation of ternary salt
systems. In particular, we suggested that compound
formation inside the triangular diagram involving
cesium, zinc, and zirconium molybdates will be influꢀ
enced by a structural factor, above all, the structure of
Cs Zn (MoO ) and Cs Zn(MoO ) double molybꢀ
0
.1
1
1
1
1
01.5
01.0
00.5
00.0
0
–
–
–
0.1
0.2
0.3
6
5
4 8
2
4 2
dates. The existence of two phases (S1 and S2) both for
manganese and zinc cations implies an insignificant
influence of structures of double molybdates of cesium
and divalent metals on the formation of complex salts.
The construction of subsolidus phase diagrams for
the Cs MoO –MMoO –Zr(MoO ) (M = Mn, Zn)
9
9.5
9.0
8.5
–0.4
–0.5
9
2
4
4
4 2
Peak 677.5°С
systems revealed two new groups of triple molybdates
differing in tetravalent zirconium contents. The possiꢀ
bility of existence of compositionally and structurally
similar triple molybdates of other divalent metals, e.g.,
magnesium and cobalt, was not also ruled out.
–
–
–
0.6
0.7
0.8
9
98.0
Peak 794.3
°
C
400
500
600
700
800
900
°
300
T
,
C
Indeed, as a result of studying the Cs MoO –
2
4
(b)
DSC,
μ
V/mg
Exo
МMoO –Zr(MoO ) (M = Mg, Co) systems, we
revealed new triple molybdates of compositions
4 4 2
TG, %
00
1
0.8
Cs МZr (MoO ) (1 : 1 : 2) and Cs МZr(MoO )
2
2
4 6
2
4 4
(
1 : 1 : 1), which were prepared as single phases by
95
90
85
80
75
70
65
0
.6
.4
.2
ceramic technology from Cs MoO , MgMoO (or
2
4
4
CoMoO4), and Zr(MoO4)2 under the conditions simꢀ
ilar to the synthesis of cesium manganese zirconium
molybdates. As probed by powder Xꢀray diffraction, the
0
0
0
1
: 1 : 2 and 1 : 1 : 1 phases are isostructural to their
manganese and zinc analogues. Table 2 compiles crysꢀ
tallographic parameters of these groups of comꢀ
pounds.
Incongruent melting was observed for triple molybꢀ
dates containing monovalent metals, divalent metals,
and zirconium. Figure 2 shows DSC curves for magꢀ
nesium phases recorded on a thermal analyzer.
–
–
0.2
0.4
Peak 848.8°C
Cs МgZr(MoO ) melts incongruently at 678
°С
. The
DSC curve for this sample features a second endotꢀ
herm at 794 ; we assigned it to liquidus melting.
2
4 4
400
500
600
700
800
900
T, °C
°С
Cs МgZr (MoO ) triple molybdate melts incongruꢀ
Fig. 2. DSC curves for (a) Cs MgZr(MoO ) and (b)
2
2
4 6
2
4 4
Cs МgZr (MoO ) .
ently at 849°С. Unfortunately, in this case we failed to
2
2
4 6
detect the liquidus melting temperature because of a
limited temperature range of record.
Xꢀray diffraction patterns of these phases signify that
they are isostructural to Cs MnZr(MoO ) and
2
4 4
Crystal Structure of Cs2
МnZr (MoO )
2 4 6
Cs МnZr (MoO4)6, respectively. Crystal data for cesium
2
2
zinc zirconium molybdates are listed in Table 2.
This structure was solved by a direct method
assuming centrosymmetric space group , which
R⎯3
The results of our experimental study of phase
was not at variance with the systematic absences
revealed. The positions found for the metal atoms (a
sixfold position on a threefold axis for Cs, a general
position for Mo, and a ninefold position in the center
of symmetry for Mn and Zr) dictated a random atom
distribution in the last position with an occupancy of
equilibria in the Cs MoO –ZnMoO –Zr(MoO )
2
4
4
4 2
system are illustrated by Fig. 1b. ZnMoO –S1
,
S1–
4
Cs Zr(MoO ) , S1–Cs Zn (MoO ) , Cs Zr(MoO ) –
2
Cs Zn (MoO ) , Cs Zn (MoO ) –Cs Zr(MoO ) ,
4 3
6
5
4 8
2
4 3
6
5
4 8
6
5
4 8
8
4 6
Cs Zn(MoO ) –Cs Zr(MoO ) , ZnMoO –S2
,
S2–
2
4 2
8
4 6
4
Cs Zr(MoO ) , S1
–S2, and S2–Zr(MoO4)2 quasiꢀ
2
4 3
2
/3 Zr + 1/3 Mn. The positions of all four basal oxyꢀ
binary joins divide the system into nine secondary triꢀ
angles.
gen atoms lying in general positions were found from
difference electron density maps. The anisotropic
Having chosen zinc molybdate, we were able to refinement of the positional and thermal parameters
took into account the stoichiometric and structural of basal atoms took into account merohedral twinꢀ
variety of double molybdates existing in the ning; the refined volumes of the twin components
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 5 2010

PHASE FORMATION
775
Table 3. Positional and equivalent isotropic thermal parameters for basal atoms in the Cs MnZr (MoO ) structure
2
2
4 6
U* , Å2
Atom
x
/
a
y
/b
z/c
eq
Cs
0
0
0.33269(5)
0.14421(2)
0.5
0.0455(2)
0.0197(1)
0.0168(1)
0.0467(10)
0.0383(8)
0.0451(10)
0.0392(9)
Mo
0.14482(3)
0.5
0.30066(3)
0.5
M**
O(1)
O(2)
O(3)
O(4)
0.1762(5)
0.2309(4)
0.1598(4)
–0.0012(3)
0.4191(4)
0.2411(4)
0.3355(5)
0.1898(4)
0.2220(4)
0.1824(3)
0.0042(3)
0.1677(4)
Notes: * Ueq = 4(U11 + U22 + 0.75U33 – U )/9.
12
** M = 2/3Zr + 1/3Mn.
Table 4. Selected interatomic distances (Å) in the Cs MnZr (MoO ) structure
2
2
4 6
Moꢀtetrahedron
Mo–O(1)
Mꢀoctahedron
Csꢀpolyhedron
1.714(4)
1.757(3)
1.767(4)
1.796(4)
1.7585
M–O(2)
M–O(4)
M–O(3)
2.074(4)
2.085(3)
2.087(3)
2.082
×
×
×
2
2
2
Cs–O(1)
Cs–O(4)
Cs–O(2)
Cs–O(3)
Cs–O(1')
3.219(5)
3.255(4)
3.664(5)
3.854(6)
3.984(6)
×
×
×
×
×
3
3
3
3
3
Mo–O(2)
Mo–O(3)
Mo–O(4)
〈M–O
〉
〈
Mo–O
〉
relate as 0.532(2) : 0.468(2). Xꢀray crystal data for torted octahedron around Cs, which is supplemented
Cs MnZr (MoO ) are compiled in Table 1, the coorꢀ by three (2) atoms (Cs–O(2), 3.664 Å) to a nineꢀ
dinates of basal atoms are listed in Table 3, and coordinate polyhedron having an approximately hexꢀ
О
2
2
4 6
selected interatomic distances are in Table 4.
agonal lower base built of
upper triangular base built of
three triangular lateral faces and three rectangular
ones. Adding three (3) atoms to this polyhedron at
Cs–O(3) distances of 3.854 Å, centering rectangular
faces, give rise to a 12ꢀcoordinate polyhedron flatꢀ
tened along the triple axis, having 14 triangular and
three rectangular faces. Lastly, the buildup of this
polyhedron to 15ꢀtope with one more triad of O(1)
atoms at Cs–O(1) distances of 3.984 Å renders the
coordination environment of a cesium atom most isoꢀ
metric.
О
(2) and
О(4) atoms and an
О(1) atoms, as well as
In the Cs МnZr (MoO ) crystal structure, molybꢀ
2
2
4 6
denum atoms each have an ordinary tetrahedral oxyꢀ
gen coordination with Mo–O distances of 1.714–
О
1
.796 Å, while (Zr,Mn) atoms have an octahedral
environment with M–O bond lengths of 2.074–2.087
Å, a value close to Zr–O distances in ꢀZr(MoO4)2
21] and Cs Zr(MoO ) [22]. Coordination of a Cs
α
[
8
4 6
atom is not definite. In the coordination sphere of a Cs
atom ( Å), 9 to 15 nearest neighbors may be recognized
4
with Cs–O distances of 3.219–3.984 Å (Table 3), comꢀ
parable with the respective bond lengths in
Cs Cd (MoO ) [23] and Cs Mo O [24]. The nearꢀ
The Cs МnZr (MoO ) structure is a new type
2
2
4 3
2
2
7
2
2
4 6
estꢀneighboring oxygen atoms at Cs–O(1) distances of where alternating molybdenum tetrahedra and
3.219 Å and Cs–O(4) distances of 3.255 Å form a disꢀ (Mn,Zr) octahedra are linked via shared oxygen corꢀ
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 5 2010

776
TSYRENOVA et al.
(а)
b
a
MoO4
(Zr, Mn)O6
Cs
(b)
c
b
а
(Zr, Mn)O6
Cs
MoO4
Fig. 3. Crystal structure of Cs МnZr (MoO4)6: (a) projection on plane (001) and (b) a polyhedral void around a cesium atom.
2
2
ners to form an original threeꢀdimensional mixed edges of the unit cell. On the one hand, this explains
framework involving all octahedral corners and three the merohedral twinning of crystals; on the other, it is
of the four tetrahedral corners (Fig. 3a). Wide chanꢀ possible that the symmetry of triple molybdate crystals
nels of the framework running parallel to axis с accomꢀ
is heightened to space group
elevation.
R3 m upon temperature
+
modate pairs of Cs cations, because of the division of
the intrachannel space into a chain of large voids, each
void containing two cesium cations with Cs–Cs disꢀ
tances of 4.083(1) Å (Fig. 3b).
Crystal Structure of Cs2
The solution of this structure was eased by its
structure type [15].
МnZr(MoO4)4
Figure 3a shows that the Cs МnZr (MoO ) strucꢀ
2
2
4 6
ture has mirror pseudoplanes normal to the lateral belonging to the KAl(MoO )
4 2
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 5 2010

PHASE FORMATION
777
Table 5. Positional and equivalent isotropic thermal parameters for basal atoms in the Cs MnZr(MoO ) structure
2
4 4
U* , Å2
Atom
x
/
a
y
/b
z/c
eq
Cs
0
0
2/3
1/2
0.0273(2)
0.0128(2)
0.0137(3)
0.0300(14)
0.0306(8)
Mo
1/3
0
0.22358(7)
0
M**
O(1)
O(2)
0
1/3
2/3
0.4354(8)
0.1555(4)
0.1669(3)
0.3338(7)
Notes: * Ueq = 4(U11 + U22 + 0.75U33 – U )/9.
12
** M = 1/2Zr + 1/2Mn.
Table 6. Selected interatomic distances (Å) in the Cs MnZr(MoO ) structure
2
4 4
Moꢀtetrahedron
Mꢀoctahedron
Csꢀpolyhedron
Mo–O(1)
Mo–O(2)
Mo–O
1.709(6)
1.770(3)
1.755
M–O(2)
2.103(3)
×
6
Cs–O(2)
Cs–O(1)
3.252(4)
3.411(1)
×
×
6
6
×
3
〈
〉
However, to check whether this is so we chose an indeꢀ lengths (2.103 Å) close to average Zr–O distances in
pendent way of using direct methods for structure
ꢀZr(MoO4)2 [21] and Cs Zr(MoO ) [22]. Position
α
8
4 6
solution in centrosymmetric space group , this 1(
b) with symmetry 3 m is occupied by Cs atoms,
P
3
m1
space group corresponding to both the symmetry of which are surrounded by an icosahedral array of 12
the analogue and the systematic absences revealed. oxygen atoms; the six of these oxygen atoms forming
The three positions of basal atoms found in this way shorter Cs–O(2) bonds (3.252 Å) constitute the upper
and lower triangular bases of the coordination polyheꢀ
(
positions 1(
a), 1(b), and 2(d) with symmetry 3 m,
dra, and the six longer Cs–O(1) bonds (3.411 Å) form
a corrugated hexagon between these bases.
3
m, and 3m, respectively) and two positions of oxygen
atoms found then from the difference electron density
maps, allowed us to verify that the compound is isosꢀ
tructural to KAl(MoO4)2 and to reveal the random
occupation of the position 1(a) by a 0.5Zr + 0.5Mn
mixture. The anisotropic refinement of the coordiꢀ
nates and thermal parameters of basal atoms conꢀ
The projection of the Cs MnZr(MoO ) structure
2
4 4
on plane (001) (Fig. 4a) demonstrates its complete
resemblance with the KAl(MoO4)2 [15] analogue, difꢀ
fering in fact only in scale and random occupation of
3+
2+
4+
Al octahedral positions by a 0.5М + 0.5Zr mixꢀ
ture. The base of this structure is the alternating layers
of oxygenꢀcornerꢀsharing MoO4 tetrahedra and
verged to
R = 0.0247. Xꢀray structure data for
Cs MnZr(MoO ) are compiled in Table 1, refined
2
4 4
(
Mn, Zr)O6 octahedra, which are well seen in Fig. 4a;
the same layer constitution is found in the
ꢀZr(MoO4)2 structure [21]. Translationally identical
coordinates of basal atoms are listed in Table 5, and
selected interatomic distances are in Table 6.
α
polyhedral layers are separated by interlayers of cesium
cations, the latter lying in between (Mn, Zr)O6 octaheꢀ
dra in icosahedral voids formed by six MoO4 tetraheꢀ
dra, the upper and lower layers adjacent to Cs each
delegating three tetrahedra. These tetrahedra share
In the Cs MnZr(MoO ) structure, position 2(
with symmetry 3m is occupied by molybdenum atoms,
which have a tetrahedral oxygen coordination with
Mo–O distances of 1.709–1.770 Å. (Zr,Mn) atoms
d
)
2
4 4
+
reside in position 1(a) with symmetry 3 m, and each have edges with CsO12 icosahedra, which are in turn linked
an octahedral environment with equivalent M–O bond via sextets of shared equatorial O(1)–O(1) edges into
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 5 2010

778
TSYRENOVA et al.
(а)
b
a
(
b)
b
а
MoO4
Fig. 4. Crystal structure of Cs МnZr(MoO4)4: (a) projection of a layer built of MoO4 tetrahedra and (Mn,Zr)O octahedra on
2
6
plane (001), where circles indicate cesium atoms; and (b) a continuous layer of CsO12 icosahedra projected on plane (001).
a continuous hexagonal honeycomb layer (Fig. 4b).
Sandwiched” of these layers fully accommodate
MoO4 tetrahedra, and (Mn, Zr)O6 octahedra appear
4. M. Chakir, A. El Jazouli, and D. de Waal, J. Solid State
Chem. 179, 1883 (2006).
5. M. Barré, M. P. CrosnierꢀLopez, F. Le Berre, et al.,
“
J. Solid State Chem. 180, 1011 (2007).
hollows between such icosahedral layers.
6
. V. M. Zhukovskii, Doctoral Dissertation in Chemistry
Sverdlovsk, 1973).
7. ICDD PDFꢀ2 Data Base, Card nos. 00ꢀ024ꢀ0276, 00ꢀ
38ꢀ1466, 01ꢀ072ꢀ0289, 01ꢀ073ꢀ1331, 00ꢀ035ꢀ0765,
1ꢀ072ꢀ2153.
. A. M. Zakharov, Binary and Ternary Phase Diagrams
Metallurgiya, Moscow, 1978) [in Russian].
(
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