Rational synthesis and X-ray structure of[MnII
4 (H2O)2(AsVW9O34)2]10� from [AsIII4 W40O140]28�, MnO4
� andMn2�
Cristina Rosu a,*, Debbie C. Crans b,*, Timothy J.R. Weakley c
a Department of Inorganic Chemistry, Babes-Bolyai University, Cluj-Napoca, Romaniab Department of Chemistry, Colorado State University, Fort Collins, CO 80523-1872, USA
c Department of Chemistry, University of Oregon, Eugene, OR 97403, USA
Received 15 October 2001; accepted 25 January 2002
Abstract
The rational synthesis of an arsenic(V) oxopolymetalate cluster from an arsenic(III) oxopolymetalate cluster has been
accomplished by a redox reaction. The sandwich Mn-complex of AsVW9O349�(Na9K[MnII
4 (H2O)2(AsVW9O34)2] �/35H2O (1) was
prepared from a tetrameric complex [As4W40O140]28� containing AsIIIW9O339� units using both MnVII and MnII salts as reagents.
Structures of 1 and Na27K[As4W40O140] �/56H2O (2), are reported. # 2002 Elsevier Science Ltd. All rights reserved.
Keywords: Heteropolyoxometalate; Arsenic; Tungstate; Lacunary; Synthesis; Redox chemistry
1. Introduction
The synthesis of large and giant oxomolybdates and
oxotungstates requires access to good starting materials
and synthetic routes.[1,2] Specifically, a large heteroox-
otungstate of composition AsIII12 CeIII
16 (H2O)36W148-
O524]76� has been reported [2] and can be described as
originating from building blocks of lacunary anions
such as AsIIIW9O339� [2�/9]. Building blocks such as
AsVW9O349� [10�/12] has been used when forming
oxometalates containing As in oxidation state V. In
this paper we show that AsIII�/AsV oxometalates can be
linked through redox chemistry and synthetic strategy.
The first precursor, AsW9O339� was initially prepared
by Tourne et al. from As2O3, Na2WO4 and HCl [6]. At
this time dimeric [3,4,10], trimeric [5,6] and tetrameric
structures [2,7�/9] have all been reported. Tetrameric
structures, containing four units of AsW9O339�, are
linked through WO22� groups and are also bonded to
Na [2], Co [8], or Mn [9]. The sandwich anions consist of
two AsIIIW9O339� units linked by three metal atoms and
have been reported with Cu, Mn, Co, and V [3,4]. The
AsV sandwich compounds are linked by four metal ions,
and those containing Zn, Co, Cu and Mn have been
structurally characterized [10�/12].This paper describes the synthesis and structure of the
mixed sodium-potassium salts of the Mn-sandwich
AsVW9O349�complex (Na9K[MnII
4 (H2O)2(AsVW9O34)2] �/35H2O) and the tetrameric condensation product of
AsIIIW9O339� (Fig. 1, Na27K[As4W40O140] �/56H2O)).
This work supplements structural findings [7,12] that
were published while this work was in progress. More
importantly, the synthetic approaches to these materials
were previously limited by the starting materials het-
eroatom oxidation state. The concept of using a redox
agent as part of the synthetic strategy is illustrated and
thus allows application of a greater number of pre-
cursors for oxometalate synthesis. In this work we show
by employing redox chemistry in the synthetic strategy,
that an oxotungstate in the AsIII class of compounds can
be converted to an oxometalate in the AsV class of
compounds.
* Corresponding author. Tel.: �/1-970-491-7635; fax: �/1-970-491-
1801.
E-mail addresses: [email protected] (C. Rosu),
[email protected] (D.C. Crans).
Polyhedron 21 (2002) 959�/962
www.elsevier.com/locate/poly
0277-5387/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S 0 2 7 7 - 5 3 8 7 ( 0 2 ) 0 0 9 1 5 - 4
2. Experimental
2.1. Reagents, solvents and procedures
The reagents were obtained from Merck and used
without further purification. Elemental analyses were
carried out by the microanalysis laboratories of ‘Babes-Bolyai’ University, Cluj-Napoca, Romania. Tungsten,
manganese, sodium, potassium and arsenic were deter-
minated by ICP. Water was determined by thermogravi-
metric analyses (TGA). Thermogravimetric studies (20�/
300 8C) were carried out with a MOM-OD 102 Paulik
Erday thermoanalyser, at a heating rate of 10 8C min�1
and 250 mg sample.
2.2. Preparation of Na27K[AsIII4 W40O140] �/56H2O
The synthesis described in the literature was modified
slightly [7]. An aqueous solution of Na2WO4 �/2H2O (33
g, 100 mmol) in 100 ml water was adjusted to pH 4.5
with glacial acetic acid and maintained at this pH for 5
min. The solution was heated to the boiling point andAs2O3 (0.99 g, 5 mmol) in 11 M HNO3 (1.3 ml) was
added slowly under vigorous stirring. For stabilization
and crystallization of the compound 0.211 g (2.68 mmol)
KCl was added. The resultant clear, pale-yellow solution
was heated under reflux for 1 h. In the event insoluble
impurities formed, these were removed by filtration
while the solution was hot. After 4�/5 days of slow
evaporation at ambient temperature prismatic colorlesscrystals were formed. The yield was 24.6 g (2.13 mmol,
85%). Recrystallization from hot water generated more
uniform crystals. IR(cm�1): 1640(m), 950(sh), 862(w),
750(sh), 690(m), 580(m), 510(w). 183W NMR (D2O�/
H2O; Na2WO4 (0 ppm) �/100, �/110, �/119, �/138,
�/191 and �/200 ppm. Elemental Analyses (%): Found:
W, 63.53; As, 2.31; Na, 5.35; K, 0.35; H2O, 8.75. Calc.:W, 63.60; As, 2.59; Na, 5.37; K, 0.34; H2O, 8.72%.
2.3. Preparation of Na9K[MnII4 (H2O)2(AsVW9O34)2] �/
35H2O
Na7KAs4W40O140 �/56H2O (2.89 g, 0.251 mmol) was
dissolved in 25 ml of water. Solutions of 0.143 g (0.633
mmol) of KMnO4 in 5 ml of water and 0.431 g (1.76
mmol) of Mn(OAc)2 �/4H2O in 5 ml of water were addeddrop-wise in an alternating fashion. The reaction
mixture was then stirred for 30 min at 70 8C. Insoluble
impurities were filtered off while the solution was hot,
and the solution was left at ambient temperature.
Yellow�/orange crystalline plates of Na9K[MnII4 (H2O)2-
(AsVW9O34)2] �/35H2O were obtained after 10 days. The
yield was 2.1 g (0.37 mmol, 74%). IR(cm�1): 1642(m),
945(sh), 904(m), 858(w), 748(sh), 575(m), 510(w). Ele-mental Analyses(%): Found: W, 58.30; As, 2.55; Mn,
3.88; Na, 3.70; K, 0.65; H2O, 11.75. Calc.: W, 58.27; As,
2.64; Mn, 3.87; Na, 3.64, K, 0.68; H2O, 11.72%.
2.4. Crystal structure analyses
Data were collected by use of a Nonius CAD4 serial
diffractometer. Table 1 contains a summary of crystaldata and the final residuals for each compound. A more
extensive table including particulars of data collection
and structure refinement is provided in the supplemen-
tary material. The orientation parameters and cell
dimensions were obtained from the diffractometer
setting angles for 25 centered reflections. Data were
corrected for absorption on the basis of azimuthal (c )
scans. A SIR-92 E-map [13] showed all non-oxygenatoms of each polyoxoanion and many oxygen and
sodium atoms. The TEXSAN program suite [14] was used
in all calculations. Hydrogen atoms were not located or
included in the refined model.
2.4.1. Na27K[AsIII4 W40O140] �/56H2O
A crystal of dimensions 0.11�/0.14�/0.25 mm was
mounted on a fiber and protected with a coating ofepoxy. The 4/m Laue symmetry, lack of systematic
absences other than those due to the I-centering, and
acentric distribution of intensities indicated the space-
group I/4: An atom clearly present at the 4 site at the
center of the tetramer was identified as K on the basis of
distances from O atoms, though its rather high refined
thermal parameter may imply that the site is also partly
occupied by a water molecule. Four of the sevenindependent Na atoms appeared to require fractional
occupancy factors [Na(4�/7), identified from bond
lengths to oxygen]; altogether 22 Na were located per
Fig. 1. The structure of the anion in Na27K[As4W40O140] �/56H2O.
C. Rosu et al. / Polyhedron 21 (2002) 959�/962960
tetramer, it is likely that others are present but
disordered. The As and W atoms and Na(1,2,3) were
refined anisotropically. Anisotropic refinement of anion
oxygen atoms led to many non-positive-definite ellip-
soids, and the results given here are for isotropically-refined oxygens and illustrated in Fig. 1.
2.4.2. Na9K[MnII4 (H2O)2(AsVW9O34)2] �/35H2O
A yellow plate of dimensions 0.07�/0.22�/0.41 mm
was secured by a trace of glue in a capillary containing
mother-liquor. The triclinic symmetry together with the
centric distribution of intensities indicated the space-
group P/1: A total of five independent Na atoms were
located, but one required a site occupancy factor of 0.5
for a satisfactory refinement. Five of the 20 independent
water oxygens also appeared to be on half-occupiedsites. The K atom whose presence was implied by the
elemental analysis could not be located, and may be
disordered over the sites of non-ligand water molecules.
All atoms except oxygen atoms of water molecules were
refined anisotropically.
3. Results and discussion
3.1. Synthesis of AsIII�/oxotungstate tetramer
The synthetic strategy for formation of the tetrameric
condensation product illustrated in 1 was modifiedslightly from that reported by Leyrie and Herve [9].
The precursor sodium arsenite was replaced by As2O3,
which was dissolved in 11 M HNO3. Also the HCl was
replaced by glacial acetic acid and HNO3. This proce-
dure was found to generate X-ray quality crystals
directly from the reaction solution, although recrystalli-
zation from water resulted in a preparation with uni-
form crystal size.
40Na2WO4�2As2O3�52HOAc�KCl
0 Na27K[As4W40O140]�NaCl�52NaOAc
�26H2O (1)
3.2. Synthesis of AsV�/oxotungstate sandwich compound
Attempts to modify the AsIII in the tetrameric
condensation product to form the AsV series compoundswere explored using an oxidation reagent that is mild
but yet sufficient to accomplish the oxidation. MnO4� is
commonly used to oxidize AsIII to AsV and was tried
initially, but proved to be an unsuitable reagent.
Furthermore, when treating solutions of tetramer with
MnO4�, no change in color could be observed over
several days. In the synthesis of complex oxometalates
in molybdenum chemistry it is common to use reagentswhich involved two different oxidation states of the
metal ion in order to achieve the desired redox potential
in the reaction solutions. This approach was adapted in
this system. Thus, the addition of both MnO4� and
Mn(OAc)2 did prove to be successful and the resulting
reaction is shown in Eq. (2). The colorless solution turns
violet upon addition of MnO4� which followed by
addition of Mn(OAc)2 changes the violet solutionbrown; the color continues to change for 5 h after
which time the solution is deep orange. Although some
flexibility exists with regard to the exact ratio of
components, best yields were obtained when 1 equiv.
of tetramer was treated with a threefold excess of
MnO4� and a sevenfold excess of Mn2� salt. When
Mn(OAc)2 was added to solutions of tetramer the color
changed to yellow indicating a replacement of cations,however, only very small light yellow crystals were
obtained. We conclude, that both redox states of the
reagent were necessary to achieve the conversion of the
Table 1
Crystallographic data for compounds Na27K[As4W40O140] �/56H2O and
Na9K[MnII4 (H2O)2(AsVW9O34)2] �/35H2O
Composition Na27K[As4W40O140] �/56H2O
Formula weight 11562.3
Space-group I/4/
a , b (A) 19.491(2)
c (A) 25.783(3)
V (A3) 9795(2)
Z 2
Dcalc (g cm�3) 3.920
T (8C) 23
l (A) 0.71073
m (cm�1) 242
Relative transmission coefficient 0.571�/1.000 (c )
Observed reflections 3831 [I ]/s (I )]
Total independent reflections 4687
R (F ), wR (F ) (observed) 0.050, 0.052
R (F 2), wR (F 2) (total) 0.091, 0.108
Composition Na9K[Mn4As2W18O70H4] �/35H2O
Formula weight 5679.4
Space-group P/1/
a (A) 11.6368(12)
b (A) 14.2113(16)
c (A) 17.6343(20)
a (A) 98.876(9)
b (8) 105.682(9)
g (8) 113.290(9)
V (A3) 2463.9(7)
Z 1
Dcalc 3.824
T (8C) 22
l 0.71073
m (cm�1) 223.0
Relative transmission coefficient 0.322�/1.000 (c )
Observed reflections 5812 [I ]/s (I )]
Total independent reflections 7160
R (F ), wR (F ) (observed) 0.038, 0.042
R (F 2), wR (F 2) (total) 0.059, 0.081
R (F )�/SjjFoj�/jFcjj/SjFoj, wR (F 2)�/[Sw (jFoj2�/jFcj2)2/Sw jFoj4]1/2.
C. Rosu et al. / Polyhedron 21 (2002) 959�/962 961
AsIII oxometalate to the AsV oxometalate. In addition to
providing an example of linking these two classes of
compounds, this method significantly improves the yield
of the synthesis of this type of material [7].
2Na27K[As4W40O140]�4KMnO4�14Mn(OAc)2
�12H2O
0 4Na9K[Mn4(H2O)2(AsW9O34)2]�8WO3�2MnO2
�2KOAc�18NaOAc�8HOAc (2)
3.3. Structure of Na27K[AsIII4 W40O140] �/56H2O
The tetrameric anion [As4W40O140]28� consists of
four a-B-AsIIIW9O33 units sharing octahedron corners
with four linking WO6 groups [W(10)]. It generallyresembles the anion in Na28[(a-B-AsO3W9O30)4(WO2)4] �/2NaCl �/55H2O that was reported while this work was in
progress [7]. The structure differs from that of the anion
in (NH4)28Co2As4W40O140 �/20�/22H2O [8] in the follow-
ing details. The point symmetry of the anion is exactly,
rather than approximately 4: The site designated [8] S1
at the center of the tetramer is occupied by K� instead
of by NH4�, bonded to the two cis O atoms of each
bridging WO6 group that are not involved in W�/O�/W
linkages. The four S2 sites [8] are all occupied by Na�
cations [Na(1)] instead of by two Co2� and two NH4�.
The four oxygens of the anion bonded to Na(1) define
an approximate square which is planar to within one
standard deviation (0.03 A), and Na(1) lies 0.63(1) A
from the plane on the side away from the As atom with
a possible weak bond [2.82(2) A] to a water oxygen atom[O(43)] in an apical position. The As� � �Na(1) distance
[3.26(1) A] is to be contrasted with the short (2.65 A)
As� � �Co distance [8] in the other anion, where the Co is
effectively six-coordinate. The differences from the
anion in Na28[(a-B-AsO3W9O30)4(WO2)4] �/2NaCl �/55H2O include the potassium, rather than sodium,
central cation and the higher (/4) crystallographic point
symmetry.
3.4. Structure of Na9K[MnII4 (H2O)2(AsVW9O34)2] �/
35H2O
The product of reaction (2) is [MnII4 (H2O)2-
(AsVW9O34)2]10�. The assumed degree of hydration of
the salt is based on the X-ray analysis. The anion lies on
a crystallographic center of symmetry, with approximatepoint symmetry 2/m (C2h ) and contains a planar set of
four Mn2� ions separating two a-B-AsW9O349� groups.
Two Mn atoms each carry one water ligand. The anion
is isostructural with the [CoII4 (H2O)2(PVW9O34)2]10�
[15], [MnII4 (H2O)2(PVW9O34)2]10� [15], and [CoII
4 (H2O)2-
(AsVW9O34)2]10� anions [10,11], with similar corre-
sponding dimensions. The all-potassium salt
K10[MnII4 (H2O)2(AsVW9O34)2] �/18H2O, was reported
while this work was in progress [12].
4. Supplemental material
Supplementary data are available from Fachinforma-
tionszentium Karlsruhe (FIZ) for Na27K[AsIII4 W40O140] �/
56H2O the number is 412184 and for Na9K[MnII4 -
(H2O)2(AsVW9O34)2] �/35H2O the number is 412183.
Acknowledgements
C.R. and D.C.C. thank the Humboldt Foundationfor a Fellowship and Research Award, respectively.
D.C.C. also thanks The Institute of General Medicine of
the National Institutes of Health for funding. We thank
Dr. Tiberiu Frentiu for the microanalyses at the
Analytical Laboratory of the Department of Chemistry
of ‘Babes-Bolyai’ University, Cluj-Napoca, Romania.
We also thank Dr. Christopher D. Rithner and Dr.
Jason Smee for recording the 183W NMR spectra for us.
References
[1] A. Muller, F. Peters, M.T. Pope, D. Gatteschi, Chem. Rev. 98
(1998) 239.
[2] K. Wasserman, M.H. Dickman, M.T. Pope, Angew. Chem., Int.
Ed. Engl. 36 (1997) 1445.
[3] F. Robert, M. Leyrie, G. Herve, Acta Crystallogr., Sect. B 38
(1982) 358.
[4] P. Mialane, J. Marrot, E. Riviere, J. Nebout, G. Herve, Inorg.
Chem. 40 (2001) 44.
[5] K.-C. Kim, M.T. Pope, J. Chem. Soc., Dalton Trans. (2001) 986.
[6] C. Tourne, A. Revel, G. Tourne, M. Vendrell, CR Acad. Sci.
Paris Ser. C 277 (1973) 643.
[7] K. Wasserman, M.T. Pope, Inorg. Chem. 40 (2001) 2763.
[8] F. Robert, M. Leyrie, G. Herve, A. Teze, Y. Jeannin, Inorg.
Chem. 19 (1980) 1746.
[9] M. Leyrie, G. Herve, Nouveau J. Chem. 2 (1978) 233.
[10] T.J.R. Weakley, Acta Crystallogr., Sect. C, (1997), 53,
IUC9700025.
[11] H.T. Evans Jr., C. Tourne, G. Tourne, T.J.R. Weakley, J. Chem.
Soc., Dalton Trans. (1986) 2699.
[12] L.-H. Bi, R.-D. Huang, J. Peng, E.-B. Wang, Y.-H. Wang, C.-W.
Hu, J. Chem. Soc., Dalton Trans. (2001) 121.
[13] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, M.C.
Burla, G. Polidori, N. Camalli, J. Appl. Crystallogr. 27 (1994)
435.
[14] Molecular Structures Corporation, 3200A Research Forest Drive,
The Woodlands, TX 77381, USA. TEXSAN Software for Single-
Crystal Structure Analysis, version 1.7, 1997.
[15] C.J. Gomez-Garcıa, E. Coronado, P. Gomez-Romero, N. Casan-
Pastor, Inorg. Chem. 32 (1993) 3378.
C. Rosu et al. / Polyhedron 21 (2002) 959�/962962
Top Related