Syntheses, structures, and properties of Ag4(Mo2O5)(SeO4)2(SeO3) and Ag2(MoO3)3SeO3

Article abstract of DOI:10.1016/j.jssc.2007.02.020

Ag₄(Mo₂O₅)(SeO₄)₂(SeO₃) has been synthesized by reacting AgNO₃, MoO₃, and selenic acid under mild hydrothermal conditions. The structure of this compound consists of cis-MoO₂²⁺ molybdenyl units that are bridged to neighboring molybdenyl moieties by selenate anions and by a bridging oxo anion. These dimeric units are joined by selenite anions to yield zigzag one-dimensional chains that extended down the c-axis. Individual chains are polar with the C₂ distortion of the Mo(VI) octahedra aligning on one side of each chain. However, the overall structure is centrosymmetric because neighboring chains have opposite alignment of the C₂ distortion. Upon heating Ag₄(Mo₂O₅)(SeO₄)₂(SeO₃) looses SeO₂ in two distinct steps to yield Ag₂MoO₄. Crystallographic data: (193 K; MoKα, λ=0.71073 A): orthorhombic, space group Pbcm, a=5.6557(3), b=15.8904(7), c=15.7938(7) A, V=1419.41(12), Z=4, R(F)=2.72% for 121 parameters with 1829 reflections with I>2σ(I). Ag₂(MoO₃)₃SeO₃ was synthesized by reacting AgNO₃ with MoO₃, SeO₂, and HF under hydrothermal conditions. The structure of Ag₂(MoO₃)₃SeO₃ consists of three crystallographically unique Mo(VI) centers that are in 2+2+2 coordination environments with two long, two intermediate, and two short bonds. These MoO₆ units are connected to form a molybdenyl ribbon that extends along the c-axis. These ribbons are further connected together through tridentate selenite anions to form two-dimensional layers in the [bc] plane. Crystallographic data: (193 K; MoKα, λ=0.71073 A): monoclinic, space group P2₁/n, a=7.7034(5), b=11.1485(8), c=12.7500(9) A, β=105.018(1) V=1002.7(2), Z=4, R(F)=3.45% for 164 parameters with 2454 reflections with I>2σ(I). Ag₂(MoO₃)₃SeO₃ decomposes to Ag₂Mo₃O₁₀ on heating above 550 °C.

Full text of DOI:10.1016/j.jssc.2007.02.020

ARTICLE IN PRESS
Journal of Solid State Chemistry 180 (2007) 1601–1607
www.elsevier.com/locate/jssc
Syntheses, structures, and properties of Ag4(Mo2O5)(SeO4)2(SeO3)
and Ag2(MoO3)3SeO3
Ã
Jie Ling, Thomas E. Albrecht-Schmitt
Department of Chemistry and Biochemistry, 179 Chemistry Building, Auburn University, Auburn, AL 36849, USA
Received 30 January 2007; received in revised form 21 February 2007; accepted 23 February 2007
Available online 7 March 2007
Abstract
Ag4(Mo2O5)(SeO4)2(SeO3) has been synthesized by reacting AgNO3, MoO3, and selenic acid under mild hydrothermal conditions. The
structure of this compound consists of cis-MoO22+ molybdenyl units that are bridged to neighboring molybdenyl moieties by selenate
anions and by a bridging oxo anion. These dimeric units are joined by selenite anions to yield zigzag one-dimensional chains that
extended down the c-axis. Individual chains are polar with the C2 distortion of the Mo(VI) octahedra aligning on one side of each chain.
However, the overall structure is centrosymmetric because neighboring chains have opposite alignment of the C2 distortion. Upon
heating Ag4(Mo2O5)(SeO4)2(SeO3) looses SeO2 in two distinct steps to yield Ag2MoO4. Crystallographic data: (193 K; MoKa,
˚
˚
l ¼ 0.71073 A): orthorhombic, space group Pbcm, a ¼ 5.6557(3), b ¼ 15.8904(7), c ¼ 15.7938(7) A, V ¼ 1419.41(12), Z ¼ 4,
R(F) ¼ 2.72% for 121 parameters with 1829 reflections with I42s(I). Ag2(MoO3)3SeO3 was synthesized by reacting AgNO3 with
MoO3, SeO2, and HF under hydrothermal conditions. The structure of Ag2(MoO3)3SeO3 consists of three crystallographically unique
Mo(VI) centers that are in 2+2+2 coordination environments with two long, two intermediate, and two short bonds. These MoO6 units
are connected to form a molybdenyl ribbon that extends along the c-axis. These ribbons are further connected together through
˚
tridentate selenite anions to form two-dimensional layers in the [bc] plane. Crystallographic data: (193 K; MoKa, l ¼ 0.71073 A):
˚
monoclinic, space group P21/n, a ¼ 7.7034(5), b ¼ 11.1485(8), c ¼ 12.7500(9) A, b ¼ 105.018(1) V ¼ 1002.7(2), Z ¼ 4, R(F) ¼ 3.45% for
164 parameters with 2454 reflections with I42s(I). Ag2(MoO3)3SeO3 decomposes to Ag2Mo3O10 on heating above 550 1C.
r 2007 Elsevier Inc. All rights reserved.
Keywords: Transition metal selenate selenite; Transition metal selenite; Thermal behavior; Hydrothermal synthesis
1. Introduction
Au2(SeO3)2(SeO4) [10], and three early actinide-contain-
ing solids, Th(SeO3)(SeO4) [11], [C5H14N][UO2(SeO4)
(SeO2OH)] [12], and [C5H14N]4[(UO2)3(SeO4)4(HSeO3)
(H2O)](H2SeO3)(HSeO4) [13].
Mixed-valent selenate selenite compounds that contain
Se(VI) in form of SeO42ꢀ and Se(IV) in SeO23ꢀ represent a
growing family of transition metal and f-block oxoanion
solids that display new structural motifs and important
optical properties. This family includes a single mineral,
schmiederit, Pb2Cu2(OH)4(SeO3)(SeO4) [1], five lantha-
nide compounds, Er2(SeO3)2(SeO4) ꢁ 2H2O [2], La(HSeO3)
(SeO4) ꢁ 2H2O [3], Nd2(SeO4)(SeO3)2(H2O)2 [4], Pr4(SeO3)2
(SeO4)F6 [5], NaSm(SeO3)(SeO4) [5], the hydrated double
salt, Na2SeO4 ꢁ H2SeO3 ꢁ H2O [6], the five transition metal
compounds Li2Cu3(SeO3)2(SeO4)2 [7], Hg3(SeO3)2(SeO4)
[8], Fe(HSeO3)(SeO4) ꢁ H2O [9], RbFe(SeO3)(SeO4) [9], and
One of the reasons for investigating this group of
compounds is to investigate the effect that the lone-pair
of electrons on the selenite anions has on the local and
extended structures. In this regard there are several known
effects. First, small channels and cavities often form to
house the lone-pair of electrons as occurs in b-AgNpO2
(SeO3) [14]. Second, lone-pair alignment selenite can take
place to yield polar structures (e.g. in Au2(SeO3)2(SeO4)
[10] and A2(MoO3)3SeO3 (A ¼ Rb, Cs, Tl, NH4) [15].
When the latter effect occurs the materials are capable of
displaying a wide variety of important properties including
nonlinear optical behavior, as well as pyro-, piezo-, and
ferroelectricity [16,17]. In this report we disclose the
Ã
Corresponding author. Fax: +1 334 844 6959.
E-mail address: albreth@auburn.edu (T.E. Albrecht-Schmitt).
0022-4596/$ - see front matter r 2007 Elsevier Inc. All rights reserved.
doi:10.1016/j.jssc.2007.02.020

ARTICLE IN PRESS
J. Ling, T.E. Albrecht-Schmitt / Journal of Solid State Chemistry 180 (2007) 1601–1607
1602
synthesis, structure, vibrational spectroscopy, and thermal
behavior of the new Mo(VI) selenate selenite, Ag4(Mo2
O5)(SeO4)2(SeO3). This compound contains polar chains,
however, the overall structure is centrosymmetric. In
addition, we also provide information on a new member
of the A2(MoO3)3SeO3 (A ¼ Rb, Cs, Tl, NH4) family [15],
Ag2(MoO3)3SeO3, whose structure differs significantly
from previous members.
for the crystal and each exposure covered a range of 0.31 in
o. A total of 1800 frames were collected with an exposure
time per frame of 20 s for Ag4(Mo2O5)(SeO4)2(SeO3) and
10 s for Ag2(MoO3)3SeO3.
Determination of integrated intensities and global cell
refinement were performed with the Bruker SAINT (v 6.02)
software package using a narrow-frame integration algo-
rithm. A semi-empirical absorption correction was applied
using SADABS [18]. The program suite SHELXTL (v 5.1)
was used for space group determination (XPREP), direct
methods structure solution (XS), and least-squares refine-
ment (XL) [19]. The final refinements included anisotropic
displacement parameters for all atoms and a secondary
extinction parameter. Some crystallographic details are
listed in Table 1, and the final positional parameters can be
found in Tables 2 and 3. Further details of the crystal
structure investigations may be obtained from the Fachin-
formationzentrum Karlsruhe, D-76344 Eggenstein-Leo-
poldshafen, Germany (Fax: (+49)7247-808-666; Email:
crysdata@fiz-karlsruhe.de) on quoting the depository
numbers CSD 417618 and 417617 for Ag4(Mo2O5)
(SeO4)2(SeO3) and Ag2(MoO3)3SeO3, respectively.
2. Experimental
AgNO3 (99.9%, Alfa-Aesar), MoO3 (99.95%, Alfa-
Aesar), H2SeO4 (40%, Alfa-Aesar), SeO2 (99.4%, Alfa-
Aesar) and HF (48%, Alfa-Aesar) were used as received
without further purification. Distilled and Millipore filtered
water with resistance of 18.2 MO cm was used in all
reactions. SEM/EDX analyses were performed using a
JEOL JSM-7000F. Silver, molybdenum, and selenium
standards were used to calibrate the results.
Ag4(Mo2O5)(SeO4)2(SeO3) was synthesized by loading
AgNO3 (185.4 mg, 1.091 mmol), MoO3 (235.6 mg,
1.637 mmol), H2SeO4 (1.00 mL, 3.89 mmol), and 0.5 mL
water in a 23-mL PTFE-lined autoclave. The autoclave was
sealed and heated at 200 1C in a box furnace. After 3 days,
the furnace was cooled to room temperature at a rate of
9 1C/h. The reaction product contained a single phase of
pale yellow crystals immersed in a colorless mother liquor.
The product was washed with water and methanol
and allowed to dry. Yield: 271 mg (88.8% based on Ag).
EDX analysis provided Ag:Mo:Se ratio of 4:2:3
(44%:23%:33%).
Ag2(MoO3)3SeO3 was synthesized by loading AgNO3
(192.5 mg, 1.133 mmol), MoO3 (244.6 mg, 1.699 mmol),
SeO2 (62.9 mg, 0.567 mmol), HF (0.1 mL, 2.76 mmol), and
0.5 mL water in a 23-mL PTFE-lined autoclave. The
autoclave was sealed and heated at 180 1C in a box
furnace. After 4 days, the furnace was cooled to room
temperature at a rate of 9 1C/h. The product was washed
with water and methanol. Orange crystals and an
unidentified yellow powder were left to dry in the air.
Yield: 272 mg (62.1% based on Ag). EDX analysis of the
orange crystals provided a Ag:Mo:Se ratio of 2:3:1
(34%:50%:16%).
2.1.1. Vibrational spectroscopy
The IR spectra of Ag4(Mo2O5)(SeO4)2(SeO3) and
Ag2(MoO3)3SeO3 were taken from samples in KBr pellets
with using a Shimadzu IR Prestige-21 in the wave number
range of 4000–400 cmꢀ1. Raman spectroscopy experiments
were performed at room temperature using backscattering
geometry with 514.5 nm (2.41 eV) line of an argon-ion laser
and an ISA U-1000 scanning double monochromator to
disperse the Stokes Raman scattering spectra.
Table 1
Crystallographic data for Ag4(Mo2O5)(SeO4)2(SeO3) and Ag2(MoO3)3
SeO3
Formula
Ag4(Mo2O5)(SeO4)2(SeO3)
Ag2(MoO3)3SeO3
Formula mass
Color and habit
Crystal system
Space group
1116.24
Yellow, block
Orthorhombic
Pbcm (No. 57)
5.6557(3)
15.8904(7)
15.7938(7)
90
774.52
Orange, block
Monoclinic
P21/n (No.14)
7.3034(5)
11.1485(8)
12.7500(9)
90
˚
a (A)
˚
b (A)
˚
c (A)
2.1. Crystallographic studies
a (deg)
b (deg)
g (deg)
90
90
105.018(1)
90
Single crystals of Ag4(Mo2O5)(SeO4)2(SeO3) and Ag2
(MoO3)3SeO3 with dimensions of 0.106 mm ꢂ 0.072 mm ꢂ
0.035 mm and 0.102 mm ꢂ 0.052 mm ꢂ 0.028 mm, respec-
tively, were selected and mounted on two quartz fibers
with epoxy and aligned on a Bruker SMART APEX CCD
X-ray diffractometer with a digital camera. Intensity
measurements were performed using graphite monochro-
mated Mo Ka radiation from a sealed tube with a
monocapillary collimator. The intensities and positions of
reflections of a sphere were collected by a combination of 3
sets of exposure frames. Each set had a different f angle
3
˚
V (A )
Z
1419.4(1)
4
193
1002.7(2)
4
193
T (K)
˚
l (A)
0.71073
56.62
5.223
0.71073
56.58
5.131
Maximum 2y (1)
rcalcd (g cm–3
)
m (Mo Ka) (cm–1
)
149.05
0.0272
0.0661
111.78
0.0345
0.0833
R(F) for F2o42s(F2o)a
Rw(F2o)b
P
P
aRðFÞ ¼ jjFoj ꢀ jFcjj= jFoj.
P
P
b
2
1=2
RwðF2oÞ ¼ ½ ½wðFo2 ꢀ F2c Þ = wFo4ꢃꢃ
.

ARTICLE IN PRESS
J. Ling, T.E. Albrecht-Schmitt / Journal of Solid State Chemistry 180 (2007) 1601–1607
1603
Table 2
Atomic coordinates and equivalent isotopic displacement parameters for
Ag4(Mo2O5)(SeO4)2(SeO3)
3. Results and discussion
3.1. Synthesis of Ag4(Mo2O5)(SeO4)2(SeO3)
2 a
˚
Ueq (A )
Atom(site)
x
y
z
There are a number of methods that have been applied
to the synthesis of mixed-valent selenate selenite com-
pounds. Under hydrothermal conditions, SeO24ꢀ can be
reduced to SeO23ꢀ as occurs in the preparation of
Au2(SeO3)2(SeO4) [10]. In the synthesis of Nd2(SeO4)
(SeO3)2(H2O)2, a portion of the SeO24ꢀ was reduced to
SeO23ꢀ with 1,10-phenanthroline [4]. Na2SeO4 ꢁ H2SeO3 ꢁ H2O
was prepared by slow evaporation of an aqueous solution
containing Na2SeO4 and H2SeO3 at room temperature [6].
Mixed-valent Se(IV)/Se(VI) compounds can also be obtained
by oxidizing SeO2 with HNO3, e.g. in the preparation of
Er2(SeO3)2(SeO4) ꢁ 2H2O [2].
1
4
1
4
Ag(1)
Ag(2)
0.17767(10)
0.69721(10)
0.34503(4)
0.50077(3)
0.01739(13)
0.01628(13)
Ag(3)
Mo(1)
Se(1)
0.17562(7)
0.64349(7)
0.24643(12)
0.50367(2)
0.67226(3)
0.63408(4)
0.42003(3)
0.41167(2)
1
4
0.01659(11)
0.00993(11)
0.01036(14)
Se(2)
O(1)
O(2)
0.67276(8)
0.4373(6)
0.0814(10)
0.35891(3)
0.6037(2)
0.5493(3)
0.39988(3)
0.3320(2)
1
4
0.01122(12)
0.0154(7)
0.0240(12)
O(3)
O(4)
O(5)
O(6)
O(7)
O(8)
O(9)
0.3496(6)
0.6559(6)
0.9259(7)
0.4597(7)
0.1765(7)
0.7973(6)
0.6977(8)
0.7579(2)
0.3745(2)
0.3933(2)
0.4102(2)
0.2146(2)
0.5849(2)
0.3787(2)
0.5031(2)
0.3647(2)
0.3515(2)
0.1627(2)
0.4450(2)
0.0166(7)
0.0160(7)
0.0207(8)
0.0201(8)
0.0189(8)
0.0168(7)
0.0132(9)
In this work, Ag4(Mo2O5)(SeO4)2(SeO3) was prepared as
a pure phase by reacting AgNO3, MoO3, and H2SeO4
under mild hydrothermal conditions. Here some of the
SeO24ꢀ was reduced to SeO23ꢀ as occurs in the preparation
of Th(SeO3)(SeO4) [11]. There are two options for
explaining the reduction of selenate to selenite. The first
of these is that the relatively strong oxidizing power of
selenate (E1 ¼ 1.151 V) might be sufficient under these
conditions to oxidize water. Second, the selenate might
thermally decompose to yield selenite. The moderate
heating conditions used here allow for the isolation
of partially reduced compounds. The synthesis of Ag4
(Mo2O5)(SeO4)2(SeO3) is quite reproducible, and occurs in
high yield suggesting that an impurity is not responsible for
the reduction of the selenate anion.
Orange crystals of Ag2(MoO3)3SeO3 were synthesized
hydrothermally by reacting AgNO3, MoO3, SeO2, and HF.
Although fluoride is not incorporated in the com-
pound, HF apparently plays an important role in the
synthesis because attempts to prepare Ag2(MoO3)3SeO3
in the absence of HF were unsuccessful. The substitu-
tion of nitric acid for hydrofluoric acid was not
successful. Fluoride is probably serving as a mineralizing
agent.
3
4
1
2
Table 3
Atomic coordinates and equivalent isotopic displacement parameters for
Ag2(MoO3)3SeO3
2 a
˚
Ueq (A )
Atom(site)
x
y
z
Mo(1)
Mo(2)
Mo(3)
Ag(1)
Ag(2)
Se(1)
O(1)
ꢀ0.41376(5)
ꢀ0.44934(5)
0.15004(6)
0.13073(6)
ꢀ0.14522(6)
ꢀ0.15215(6)
0.2569(5)
0.40227(3)
0.80118(3)
0.81194(3)
0.94463(3)
0.93163(2)
0.05667(3)
0.69478(3)
0.8413(3)
0.0545(3)
0.8039(3)
0.9479(3)
0.9649(3)
0.8162(3)
0.0948(3)
0.8805(3)
0.9663(3)
0.9448(3)
0.1603(3)
0.1905(3)
0.00636(12)
0.00635(12)
0.00637(12)
0.01347(12)
0.01355(12)
0.00888(13)
0.0149(8)
0.0143(8)
0.0113(7)
0.0092(7)
0.0087(7)
0.0125(7)
0.0120(7)
0.0160(8)
0.0092(7)
0.0149(8)
0.0156(8)
0.0102(7)
0.07632(3)
0.08270(3)
0.41724(3)
0.24812(3)
0.19103(4)
0.0813(3)
0.0749(3)
0.0967(3)
ꢀ0.0811(3)
0.2486(2)
0.4132(3)
0.4144(3)
0.4167(3)
0.5828(3)
0.2368(3)
0.2440(3)
0.2661(3)
O(2)
O(3)
0.3410(5)
ꢀ0.1195(5)
0.0588(5)
0.0857(5)
O(4)
O(5)
O(6)
O(7)
ꢀ0.0541(5)
0.3099(5)
0.3220(5)
O(8)
O(9)
0.0986(5)
O(10)
O(11)
O(12)
ꢀ0.3352(5)
ꢀ0.2494(5)
0.1204(5)
3.2. Crystal structure of Ag4(Mo2O5)(SeO4)2(SeO3)
2.1.2. Thermal analysis
The structure of the title compound contains one
crystallographically unique Mo(VI) center in classical
2+2+2 coordination environments with two long, two
intermediate, and two short bonds. The bond distances
Mo(1) are 1.694(4), 1.721(4), 1.889(4), 2.032(4), 2.210(4),
For the investigation of the thermal behavior, 25 mg of
the title compounds were placed in two platinum pans that
were heated (5 1C/min) up to 725 1C under a nitrogen flow
using a TGA Instruments Model Q50 V5.3 Build 171. The
residue compositions were checked by power X-ray
diffraction.
2+
˚
and 2.288(4) A. The two shortest bonds define MoO2
molybdenyl units where the oxo atoms are terminal. The
Mo centers are shifted along a C2-axis of each octahedron
˚
by 0.356(1) A from the center of the six oxygen atoms. The
MoO6 units share a single corner to create dimers. The
bridging Mo(1)–O(9) bond has a bond distance of
2.1.3. Powder X-ray diffraction
Powder X-ray diffraction patterns were collected with a
Rigaku Miniflex powder X-ray diffractometer using Cu Ka
˚
˚
(l ¼ 1.54056 A) radiation. The collected patterns were
1.889(1) A, and a Mo(1)–O(9)–Mo(1) angle of 161.3(3)1
that are typical when compared with previously reported
crystallographic data of Mo2O11 units [21–23]. Within each
compared with that calculated from single crystal data
using ATOMS [20].

ARTICLE IN PRESS
J. Ling, T.E. Albrecht-Schmitt / Journal of Solid State Chemistry 180 (2007) 1601–1607
1604
dimer two selenate anions bridge the Mo(VI) centers. The
dimers are in turn linked into zigzag one-dimensional
chains by selenite anions, as is shown in Fig. 1. The chains
extend down the c-axis. Individual chains are polar with
the C2 distortion of the Mo(VI) octahedra aligning on one
side of each chain. However, the overall structure is
centrosymmetric because neighboring chains have opposite
alignment of the C2 distortion, as is depicted in Fig. 2. The
bridging selenite anions contain a stereochemically active
lone-pair of electrons that oppositely align in the b
direction, resulting in a cancellation of polarity produced
by this group. There are no long contacts between the Se
atom in the selenite anion and neighboring oxygen atoms
within the structure. Selected bond distances and bond
angles are given in Table 4. The calculated bond-valence
sum (BVS) of Mo(1) is 5.994 [24,25].
Table 4
˚
Selected bond distances (A) and angles (deg) for Ag4(Mo2O5)(SeO4)2
(SeO3)
˚
Bond distances (A)
Mo(1)–O(1)
Mo(1)–O(3)
Mo(1)–O(4)
Mo(1)–O(7)
Mo(1)–O(8)
Mo(1)–O(9)
2.032(4)
2.210(4)
2.288(4)
1.694(4)
1.721(4)
1.889(1)
Se(1)–O(1) x 2
Se(1)–O(2)
Se(2)–O(3)
Se(2)–O(4)
Se(2)–O(5)
Se(2)–O(6)
1.754(3)
1.638(5)
1.645(4)
1.651(4)
1.630(4)
1.643(4)
Angles (deg)
O(1)–Mo(1)–O(3)
O(1)–Mo(1)–O(4)
O(1)–Mo(1)–O(7)
O(1)–Mo(1)–O(8)
O(1)–Mo(1)–O(9)
O(3)–Mo(1)–O(4)
O(3)–Mo(1)–O(7)
O(3)–Mo(1)–O(8)
O(3)–Mo(1)–O(9)
O(4)–Mo(1)–O(7)
O(4)–Mo(1)–O(8)
O(4)–Mo(1)–O(9)
O(7)–Mo(1)–O(8)
75.7(1)
76.4(1)
97.4(2)
92.7(2)
154.3(2)
77.4(1)
92.6(2)
161.6(2)
83.9(1)
169.2(2)
86.1(2)
84.2(1)
154.3(2)
O(7)–Mo(1)–O(9)
O(8)–Mo(1)–O(9)
Mo(1)–O(9)–Mo(1)
98.9(2)
102.7(2)
161.3(3)
O(1)–Se(1)–O(1)
O(1)–Se(1)–O(2)
O(1)–Se(1)–O(2)
O(3)–Se(2)–O(4)
O(3)–Se(2)–O(5)
O(3)–Se(2)–O(6)
O(4)–Se(2)–O(5)
O(4)–Se(2)–O(6)
O(5)–Se(2)–O(6)
95.2(2)
97.2(2)
97.2(2)
Se(1) is coordinated by three oxygen atoms in a trigonal
pyramidal geometry with Se(1)–O bond distances of
110.0(2)
109.0(2)
109.5(2)
109.7(2)
110.0(2)
108.6(2)
˚
1.638(5) A (terminal) and 1.754(3) A (bridging). Se(2) is
˚
present in a tetrahedral environment, and has Se(2)–O bonds
˚
averaging 1.642(4) A. The calculated bond valence sums of
Se(1) and Se(2) are 3.932 and 5.897, respectively [24,25].
There are three crystallographically unique Ag+ centers
in the structure of Ag4(Mo2O5)(SeO4)2(SeO3). Ag(1) resides
in a trigonal prismatic environment with Ag–O bond
˚
distances ranging from 2.429(4) to 2.490(4) A. Ag(2) and
Ag(3) are five- and six-coordinate, respectively, and both
have highly irregular geometries. Ag(2) has Ag–O bond
˚
distances in the range of 2.306(6)–2.553(4) A, while those of
˚
Ag(3) range from 2.415(4) to 2.579(4) A. The calculated
bond valence sums of Ag(1), Ag(2), and Ag(3) are 1.001,
0.798, and 0.929, respectively [24,25].
Fig. 1. A view of the one-dimensional [(Mo2O5)(SeO4)2(SeO3)]4ꢀ chains
that extend down the c-axis in the structure of Ag4(Mo2O5)(SeO4)2(SeO3).
3.2.1. Crystal structure of Ag2(MoO3)3SeO3
Although Ag2(MoO3)3SeO3 has a similar formula with
A2(MoO3)3SeO3 (A ¼ Rb, Cs, Tl, NH4), it crystallizes in
the monoclinic space group P21/n instead of the hexagonal
space group P63 [15]. The A2(MoO3)3SeO3 (A ¼ Rb, Cs,
Tl, NH4) family of compounds consists of two-dimensional
anionic slabs related to WO3 that are capped on one side by
selenite. The structure of Ag2(MoO3)3SeO3 consists of
three crystallographically unique Mo(VI) centers that are
also in classical 2+2+2 coordination environments with
two long, two intermediate, and two short bonds. In each
MoO6 unit, three oxygen atoms are shared with four
neighboring [MoO6] units through edge- and corner-
sharing, and with one oxygen atom from the selenite
anion. The remaining two oxygen atoms are terminal with
O–Mo–O angles of 101.2(2)1, 102.4(2)1, and 102.5(2)1 for
Mo(1), Mo(2), and Mo(3), respectively. These MoO6 units
are connected to form a molybdenyl ribbon that extends
along the c-axis as is shown in Fig. 3. Selected bond
distances and bond angles are given in Table 5. The BVS
Fig. 2. A depiction of individual polar [(Mo2O5)(SeO4)2(SeO3)]4ꢀ chains
with the C2 distortion of the Mo(VI) octahedra aligning on one side of
each chain in Ag4(Mo2O5)(SeO4)2(SeO3).

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1605
values of Mo(1), Mo(2), and Mo(3) are 5.99, 6.05, and
5.98, respectively [24,25]. These ribbons are further
connected together through tridentate selenite anions to
form a two-dimensional layer in [bc] plane, and stacks
along a-axis as is shown in Fig. 4. The bridging tridentate
selenite anions have Se–O bond distances of 1.703(3),
˚
1.711(3), and 1.716(4) A, with a BVS value of 3.94 for the
selenium atom [24,25]. Unlike the A2(MoO3)3SeO3
(A ¼ Rb, Cs, Tl, NH4) family of compounds, which have
the lone-pair of electrons on the Se atoms located on one
side of the molybdenum oxide sheets as indicated by the
polar space group, as is shown in Fig. 3, the selenite groups
in Ag2(MoO3)3SeO3 have opposing orientations in each
layer.
There are two crystallographically unique Ag+ centers in
the structure of Ag2(MoO3)3SeO3. Ag(1) has Ag–O bond
˚
distances in the range of 2.400(3)–2.592(3) A, while those of
˚
Ag(2) range from 2.272(4) to 2.481(3) A. Ag(1)O6 units
Fig. 3. A view of the two-dimensional [(MoO3)3SeO3]2ꢀ layer in
Ag2(MoO3)3SeO3 that extends in the [bc] plane.
edge-share with adjacent Ag(2)O6 polyhedra. The calcu-
lated bond valence sums of Ag(1) and Ag(2) are 0.944 and
1.176, respectively [24,25].
Table 5
Selected bond distances (A) and angles (deg) for Ag2(MoO3)3SeO3
3.2.2. Vibrational spectroscopy
˚
The vibrational spectrum of Ag4(Mo2O5)(SeO4)2(SeO3)
is complex and consist of three primary regions. The
highest wavenumber region with three bands observed at
991, 954, and 945 cmꢀ1 in IR spectrum and one band at
960 cmꢀ1 in Raman spectrum is attributable to vibrational
modes from the MoO22+ units [26]. The second zone has IR
bands at 884, 868, 846, 836, and 825 cmꢀ1 that can be
assigned to stretches of the Se–O bond in the SeO24ꢀ anions
[27]. Finally, two bands in the IR are found at 781 and
726 cmꢀ1 that are attributed to the stretches of Se–O bonds
in SeO23ꢀ anions [28]. The Raman spectrum of Ag4
(Mo2O5)(SeO4)2(SeO3) shows two bands at 815 and
907 cmꢀ1 that are due to stretching modes of the SeO23ꢀ
and SeO24ꢀ, respectively. The IR and Raman spectra of
Ag4(Mo2O5)(SeO4)2(SeO3) are shown in Fig. 5.
˚
Bond distances (A)
Mo(1)–O(1)
Mo(1)–O(2)
Mo(1)–O(3)
Mo(1)–O(4)
Mo(1)–O(40)
Mo(1)–O(5)
Mo(2)–O(5)
Mo(2)–O(6)
Mo(2)–O(7)
Mo(2)–O(8)
Mo(2)–O(9)
1.697(4)
1.704(3)
2.300(3)
1.948(3)
2.300(4)
1.942(1)
1.974(3)
1.721(4)
2.152(3)
1.687(4)
1.926(3)
Mo(2)–O(90)
Mo(3)–O(40)
Mo(3)–O(5)
Mo(3)–O(90)
Mo(3)–O(10)
Mo(3)–O(11)
Mo(3)–O(12)
2.373(4)
1.972(3)
2.288(4)
1.951(3)
1.717(4)
1.687(4)
2.236(3)
Se(1)–O(3)
Se(1)–O(7)
Se(1)–O(12)
1.711(3)
1.703(3)
1.716(4)
Angles (deg)
O(1)–Mo(1)–O(2)
O(1)–Mo(1)–O(3)
O(1)–Mo(1)–O(4)
O(1)–Mo(1)–O(40)
O(1)–Mo(1)–O(5)
O(2)–Mo(1)–O(3)
O(2)–Mo(1)–O(4)
O(2)–Mo(1)–O(40)
O(2)–Mo(1)–O(5)
O(3)–Mo(1)–O(4)
O(3)–Mo(1)–O(40)
O(3)–Mo(1)–O(5)
O(4)–Mo(1)–O(40)
O(40)–Mo(1)–O(5)
O(5)–Mo(2)–O(6)
O(5)–Mo(2)–O(7)
O(5)–Mo(2)–O(8)
O(5)–Mo(2)–O(9)
O(5)–Mo(2)–O(90)
O(6)–Mo(2)–O(7)
O(6)–Mo(2)–O(8)
O(6)–Mo(2)–O(9)
O(6)–Mo(2)–O(90)
O(7)–Mo(2)–O(8)
101.2(2)
82.4(2)
103.7(2)
166.5(2)
106.8(2)
176.3(2)
98.4(2)
92.2(2)
96.6(2)
81.5(1)
84.2(1)
176.3(2)
72.4(1)
73.0(1)
91.2(2)
82.6(1)
106.3(2)
145.7(2)
72.6(1)
166.5(2)
102.4(2)
96.1(2)
87.7(2)
90.9(2)
O(7)–Mo(2)–O(9)
O(7)–Mo(2)–O(90)
O(8)–Mo(2)–O(9)
O(8)–Mo(2)–O(90)
O(9)–Mo(2)–O(90)
O(40)–Mo(3)–O(5)
O(40)–Mo(3)–O(90)
O(40)–Mo(3)–O(10)
O(40)–Mo(3)–O(11)
O(40)–Mo(3)–O(12)
O(5)–Mo(3)–O(90)
O(5)–Mo(3)–O(10)
O(5)–Mo(3)–O(11)
O(5)–Mo(3)–O(12)
O(90)–Mo(3)–O(10)
O(90)–Mo(3)–O(11)
O(90)–Mo(3)–O(12)
O(10)–Mo(3)–O(11)
O(10)–Mo(3)–O(12)
O(11)–Mo(3)–O(12)
82.7(1)
79.0(1)
104.7(2)
169.9(2)
74.3(1)
72.7(1)
107.0(2)
95.8(2)
102.1(2)
83.5(1)
75.0(1)
96.9(2)
160.4(2)
77.4(1)
94.7(2)
106.0(2)
83.0(1)
102.5(2)
174.1(2)
83.3(2)
In the IR spectrum of Ag2(MoO3)3SeO3 there are bands
at 974, 957, 950, 932, and 911 cmꢀ1 that are associated with
O(3)–Se(1)–O(7)
O(3)–Se(1)–O(12)
O(7)–Se(1)–O(12)
98.4(2)
97.3(2)
101.5(2)
Fig. 4. An illustration of the stacking of the [(MoO3)3SeO3]2ꢀ layers in
Ag2(MoO3)3SeO3.

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J. Ling, T.E. Albrecht-Schmitt / Journal of Solid State Chemistry 180 (2007) 1601–1607
1606
20000
15000
10000
5000
60
IR (upper)
IR (upper)
Raman (below)
20
10
0
Raman (below)
6000
40
20
4000
0
2000
-20
400
600
800
1000
1200
400
600
800
1000
1200
Wavenumber (cm-1)
Wavenumber (cm-1)
Fig. 5. IR and Raman spectra of Ag4(Mo2O5)(SeO4)2(SeO3).
Fig. 6. IR and Raman spectra of Ag2(MoO3)3SeO3.
stretches of the molybdenyl units. Five bands at 798, 769,
748, 692, 677, and 599 cmꢀ1 are assigned as characteristic
vibrational modes for SeO23ꢀ anions. The Raman spectrum
of Ag2(MoO3)3SeO3 shows two sharp bands at 865 and
820 cmꢀ1 and one broad band at 664 cmꢀ1 that are due to
vibrational modes of the SeO23ꢀ anions. One weak band at
899 cmꢀ1 and one sharp band at 942 cmꢀ1 are assigned to
the stretching modes of the MoO22+ units. The IR and
Raman spectra of Ag2(MoO3)3SeO3 are shown in Fig. 6.
0.20
0.15
0.10
0.05
0.00
-0.05
110
100
90
80
70
3.2.3. Thermal analysis
The thermal behavior of selenates and selenites is of
interest because there are multiple mechanisms of decom-
position including loss of oxygen by selenate and decom-
position of the selenate and selenite anions to yield
SeO2 [28,29]. The thermal decomposition of Ag4(Mo2O5)
(SeO4)2(SeO3) follows a two-step mechanism shown in
Fig. 7. The TGA curve shows the compound is thermally
stable up to 375 1C (Fig. 5). The first step of weight loss is
in the temperature range of 376–406 1C, and may
correspond to the release of SeO2 from a SeO23ꢀ anion.
The observed weight loss of 9.95% is in good agreement
with the calculated value (9.94%). The second weight loss
occurs from 469 to 510 1C can be attributed to the loss of
two SeO2 units and one O2 molecule released from two
SeO24ꢀ anions. The second experimental weight loss of
22.2% is also consistent with the calculated value (22.7%).
The powder X-ray diffraction data of the final residue
corresponds with pure Ag2MoO4 [30]. Therefore, the two-
step decomposition mechanism can potentially be de-
scribed by the following equations:
60
0
100 200 300 400 500 600 700 800
Temperature (°C)
Fig. 7. A TGA thermogram for Ag4(Mo2O5)(SeO4)2(SeO3).
550 1C. The final residue is identified as pure Ag2Mo3O10 by
powder X-ray diffraction [31]. The observed weight loss of
14.1% is close to the theoretical value of 14.3% calculated
for the elimination of one SeO2 from Ag2(MoO3)3SeO3.
4. Conclusions
In this report we have provided the details on the
syntheses, structures, vibrational spectroscopy, and ther-
mal behavior of Ag4(Mo2O5)(SeO4)2(SeO3) and Ag2
(MoO3)3SeO3. Despite the fact that both of these
compounds possess oxoanions with a stereochemically
active lone-pair of electrons, both compounds crystallize in
centrosymmetric space groups. However, both compounds
are low-dimensional, a feature that might be attributable to
the presence of the selenite anions. Both compounds
thermally decompose at elevated temperatures through
the loss of SeO2.
Ag4ðMo2O5ÞðSeO4Þ2ðSeO3Þ ! Ag4ðMoO3Þ2ðSeO4Þ2 þ SeO2
(1)
Ag4ðMoO3Þ2ðSeO4Þ2 ! 2 Ag2MoO4 þ 2SeO2 þ O2
(2)
Acknowledgments
Similar to the thermal behavior of A2(MoO3)3SeO3
(A ¼ Rb, Cs, Tl) [15], the TGA data for Ag2(MoO3)3SeO3
shows a one-step weight loss over a broad range from 350 to
This work was supported by the Chemical Sciences,
Geosciences and Biosciences Division, Office of Basic

ARTICLE IN PRESS
J. Ling, T.E. Albrecht-Schmitt / Journal of Solid State Chemistry 180 (2007) 1601–1607
1607
Energy Sciences, Office of Science, Heavy Elements
Program, US Department of Energy under Grant DE-
FG02-01ER15187.
[15] W.T.A. Harrison, L.L. Dussack, A.J. Jacobson, Inorg. Chem. 33
(1994) 6043;
L.L. Dussack, W.T.A. Harrison, A.J. Jacobson, Mater. Res. Bull. 31
(1996) 249.
[16] P.S. Halasyamani, K.R. Poeppelmeier, Chem. Mater. 10 (1998) 2753.
[17] K.M. Ok, E.O. Chi, P.S. Halasyamani, Chem. Soc. Rev. 35 (2006)
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