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The Wheel-Shaped Cu20 Tungstophosphate [Cu20Cl(OH)24(H2O)12(P8W48O184)]25 Ion.

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Angewandte
Chemie
Polyoxometalates
The Wheel-Shaped Cu20 Tungstophosphate
[Cu20Cl(OH)24(H2O)12(P8W48O184)]25 Ion**
Sib Sankar Mal and Ulrich Kortz*
Polyoxometalates are a unique class of metal-oxide clusters.
This family of compounds was discovered by Berzelius many
years ago, but only recently the full potential of these species
has been realized.[1?2] The search for novel polyanion structures is predominantly driven by the manifold applications of
these compounds in areas as diverse as catalysis, bio- and
nanotechnology, medicine, and materials science.[3?9]
The structural beauty of polyoxometalates is an additional
feature that has contributed to this class attracting so much
attention. Especially the work of Mller et al. has resulted in
discrete molecular species with spectacular sizes and symmetries. For example, they reported gigantic mixed-valence
polyoxomolybdate rings and spheres containing up to
368 molybdenum atoms.[10] Pope et al. reported a polyoxotungstate
with
148 tungsten
atoms,
[As12Ce16(H2O)36W148O524]76 .[11]
Interestingly all of the above species were synthesized
without using any polyanion precursor. It must be realized
that formation of polyanions is a self-assembly process, which
depends more on the reaction conditions (e.g. pH value,
concentration and ratio of reagents, ionic strengths) than on
the type of polyanion precursors used.
We have been interested for some time in transitionmetal-substituted polyoxotungstates, especially with respect
to their magnetic and electrochemical properties.[12] There is
interest in the synthesis of molecular species with high spin
ground states. Lately Christou et al. reported the largest
molecular magnet known to date composed of 84 manganese
atoms.[13] Until then the so called ?Mn12 acetate? had probably
been the most attractive species in the area of single-molecule
magnets.[14] Also polyoxometalate chemistry plays a major
role in this field, as it allows for a bottom-up synthesis of
paramagnetic multimetal-oxo-hydroxo clusters which are
encapsulated and stabilized by diamagnetic polyanion fragments.[5?8, 15] The magnetic and EPR properties of such
discrete clusters can be analyzed in great detail, as usually
intermolecular interactions are negligibly small.[12] Nevertheless, it must be realized that routinely polyoxotungstates with
only three or four transition-metal ions have been synthesized, and only a handful of systems containing five or more
paramagnetic centers.[12a,b, 16]
In our search for highly lacunary polyanion ligands that
might be an appropriate template for significantly larger
paramagnetic clusters we have focused our attention on the
established crown heteropolyanion [H7P8W48O184]33 .[17] This
species is composed of four [H2P2W12048]12 fragments which
are linked by capping tungsten atoms resulting in a cyclic
arrangement. The stability of [H7P8W48O184]33 in aqueous
solution over an unusually large pH range (1?8) and its large
central cavity (diameter of around 10 ) are highly attractive
features. We can consider [H7P8W48O184]33 as a superlacunary
polyanion, but surprisingly this species has been largely
neglected as a precursor.[18] This situation is probably because
Tz and Contant concluded in 1985 that [H7P8W48O184]33
?does not give complexes with divalent or trivalent transitionmetal ions?.[17a] Nevertheless, we decided to investigate in
detail the reactivity of paramagnetic 3d metal ions with
[H7P8W48O184]33 in aqueous medium.
Interaction of CuCl2 with K28Li5[H7P8W48O184] in the ratio
24:1 in aqueous medium (pH 6) resulted in the large, wheelshaped anion [Cu20Cl(OH)24(H2O)12(P8W48O184)]25 (1; Figures 1?3. Polyanion 1 crystallized as a mixed potassium-
[*] S. S. Mal, Prof. U. Kortz
International University Bremen
School of Engineering and Science
P.O. Box 750 561, 28725 Bremen (Germany)
Fax: (+ 49) 421-200-3229
E-mail: u.kortz@iu-bremen.de
[**] U.K. thanks the International University Bremen and the DFG (grant
KO 2288/3-1) for research support. U.K. also highly appreciates that
Prof. J. Kopf at Hamburg University allowed him access to the
single-crystal X-ray diffractometer. Figure 1?Figure 5 were generated
by Diamond Version 3 (copyright Crystal Impact GbR).
Angew. Chem. Int. Ed. 2005, 44, 3777 ?3780
Figure 1. Ball-and stick-representation of [Cu20Cl(OH)24(H2O)12(P8W48O184)]25 (1). Black W, turquoise Cu, yellow P, violet Cl, red O.
DOI: 10.1002/anie.200500682
2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3777
Communications
Figure 4. Ball-and-stick representation of the asymmetric unit of 1,
thermal ellipsoids shown are set at 50 % probability.
Figure 2. Combined polyhedral/ball-and-stick representation of 1. The
WO6 octahedra are red and the PO4 tetrahedra are yellow. Otherwise,
the labeling scheme is the same as that in Figure 1.
Figure 5. Ball and stick representation of the copper-hydroxo cluster in
1 showing all structurally equivalent copper atoms with the same label.
Only the oxo-ligands bridging neighboring copper ions are shown.
Figure 3. Side view of 1 showing ball-and-stick (left) and combined
polyhedral/ball-and-stick (right) representations.
lithium salt in the tetragonal system (space group I4/m).[19] As
a result, the asymmetric unit of 1 includes only six tungsten
and three copper atoms (Figure 4).
The polyanion 1 is unprecedented in structure, size, and
composition. This molecule is the first transition-metalsubstituted derivative of [H7P8W48O184]33 and it incorporates
more paramagnetic 3d metal ions than any other polyoxotungstate to date.[12a,b, 16] The structure of the wheel-shaped
[H7P8W48O184]33 precursor is maintained in 1 and the cavity is
filled with a highly symmetrical copper-hydroxo cluster
(Figure 1, Figure 2, and Figure 5). This structure emphasizes
that the template effect plays an important role during
3778
2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
formation of 1. We have shown that the oxo-groups in the
cavity of the tungstophosphate precursor [H7P8W48O184]33 do
actually interact with transition-metal ions in aqueous
medium, but some heating is required (see Experimental
Section). Therefore, [H7P8W48O184]33 can indeed be considered as a superlacunary polyanion precursor and we expect
that other transition-metal ions besides copper(ii) can also be
incorporated.
The Cu20 cluster in 1 is composed of only three structurally
unique types of copper(ii) ions (eight Cu1, four Cu2, and eight
Cu3; see Figure 5). All 20 copper centers are bridged to
neighboring copper ions by m3-oxo ligands to give a highly
symmetrical, cage-like assembly. Based on bond valence sum
calculations all 24 bridging oxygen atoms are monoprotonated.[20] The center of the cavity (which has a diameter of
around 7 ) is occupied by a chloride ion (Figure 1 and
Figure 2). The coordination numbers and geometries of Cu1,
Cu2, and Cu3 are different from each other. Cu1 is
coordinated in a strongly distorted octahedral fashion and
exhibits Jahn?Teller distortion with axial elongation. The
equatorial plane is composed of Cu1 O3 A (1.922(14) ),
Cu1 O5A (1.926(15) ), Cu1 O2C3 (1.980(14) ), and
Cu1 O1Cu (1.986(14) ) bonds. The two axial bonds are
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Angew. Chem. Int. Ed. 2005, 44, 3777 ?3780
Angewandte
Chemie
Cu1 O1C3 (2.358(16) ) and a very long bond Cu1 O5W
(2.504(17) ) to a terminal water molecule.[20] This very long
bond Cu1 O5W is not shown in Figure 4 as the bond order is
almost negligibly small (around 0.1), nevertheless, this bond is
shown in Figures 1?3. The angle O1C3-Cu1-O5W is only 1458
which reflects steric hindrance of the water ligand. Cu2 has
square-pyramidal coordination geometry with two Cu2
O2C3 (1.922(14) ) and two Cu2 O1Cu (1.925(14) )
bonds in the equatorial plane and a long bond to a terminal
water ligand, Cu2 O1C2 (2.29(3) ).[20] Finally, Cu3 has a
square-planar coordination geometry which is composed of
Cu3 O1C3 (1.905(16) ), Cu3 O1Cu (1.933(14) ), Cu3
O1C3? (1.947(16) ), and Cu3 O2C3 (1.948(14) ) bonds.
The copper?copper distances in 1 are: Cu1贩稢u2 2.812(3) ,
Cu1贩稢u3 3.045(4) , and Cu1贩稢u3? 3.052(4) .
We also investigated the solution properties of 1 by
31
P NMR spectroscopy at room temperature in D2O
(400 MHz; JEOL ECX instrument). We observed a singlet
at d = 29.3 ppm indicating that all eight phosphorus atoms
in 1 are equivalent, which is in complete agreement with the
solid-state structure (Figure 1 and Figure 2). We have not yet
obtained a good 183W NMR spectrum for 1 (expected are
three signals of equal intensity), probably due to solubility
problems.
In summary, we have synthesized a large, wheel-shaped,
Cu20 containing polyanion by direct reaction of copper(ii) ions
with [H7P8W48O184]33 . The polyanion 1 contains more paramagnetic 3d transition-metal centers than any other polyoxotungstate reported to date. Furthermore, it is stable in
solution, as shown by 31P NMR spectroscopy. Contrary to
prior reports, we have shown that the wheel-shaped
[H7P8W48O184]33 1) actually does react with transition-metal
ions in aqueous medium using simple, one-pot procedures,
2) is to be considered as a superlacunary polyanion precursor,
3) acts as a template which allows the construction of large
transition-metal-oxo clusters, and 4) is probably also reactive
towards many other electrophiles (e.g. rare earths and
organotin species). We consider [H7P8W48O184]33 as a ligand
of choice in our search for paramagnetic polyanions with high
spin ground states. Currently we are investigating the
magnetic, EPR, and electrochemical properties of 1 and
these results will be reported elsewhere. We are also
interested to see of derivatives of 1 incorporating other
transition-metals besides copper(ii) and other guests besides
Cl can be isolated. In fact, we have already prepared a
cobalt(ii)-containing derivative with a structure different from
1. Furthermore, the cage-like structure of 1 allows studies in
host?guest chemistry, ion exchange, gas storage, catalysis and
medicine to be envisaged.
Experimental Section
Preparation K12Li131� H2O: A sample of CuCl2�H2O (0.10 g,
0.60 mmol) was dissolved in a 1m LiCH3COO buffer solution
(20 mL) at pH 6.0, then K28Li5[H7P8W48O184]� H2O (0.37 g
0.025 mmol) (synthesized according to ref [17b]) was added. This
solution was heated to 80 8C for 1 h and after cooling to room
temperature it was filtered. The filtrate was allowed to evaporate in
an open beaker at room temperature. After 1?2 days a blue
crystalline product started to appear. Evaporation was allowed to
Angew. Chem. Int. Ed. 2005, 44, 3777 ?3780
continue until the solution level had approached the solid product,
which was then collected by filtration and air-dried. Yield: 0.11 g
(30 %). IR: n? = 1137(sh), 1121(s), 1080(s), 1017(m), 979(sh), 951(sh),
932(s), 913(sh), 832(sh), 753(s), 681(s), 570(sh), 523(w), 470 cm 1(w).
Elemental analysis (%) calcd for K12Li131� H2O: K 3.2, Li 0.6, W
59.2, Cu 8.5, P 1.7; found: K 3.4, Li 0.8, W 58.8, Cu 8.6, P 1.6.
Elemental analysis was performed by Kanti Labs Ltd. in
Mississauga, Canada.
Received: February 23, 2005
Published online: May 11, 2005
.
Keywords: copper � polyoxometalates � supramolecular
chemistry � template synthesis � tungsten
[1] J. Berzelius, Poggendorffs Ann. Phys. 1826, 6, 369.
[2] a) J. F. Keggin, Nature 1933, 131, 908 ? 909; b) J. F. Keggin, Proc.
R. Soc. London Ser. A 1934, 144, 75 ? 77.
[3] M. T. Pope, Heteropoly and Isopoly Oxometalates, Springer,
Berlin, 1983.
[4] M. T. Pope, A. Mller, Angew. Chem. 1991, 103, 56 ? 70; Angew.
Chem. Int. Ed. Engl. 1991, 30, 34 ? 48.
[5] Polyoxometalates: from Platonic Solids to Anti Retroviral
Activity (Eds.: M. T. Pope, A. Mller), Kluwer, Dordrecht, 1994.
[6] Chem. Rev. 1998, 98, 1 ? 389 (Special Thematic Issue on
Polyoxometalates).
[7] Polyoxometalate Chemistry: From Topology via Self-Assembly
to Applications (Eds.: M. T. Pope, A. Mller), Kluwer, Dordrecht, 2001.
[8] Polyoxometalate Chemistry for Nano-Composite Design (Eds.:
T. Yamase, M. T. Pope), Kluwer, Dordrecht, 2002.
[9] C. L. Hill, C. M. Prosser-McCartha, Coord. Chem. Rev. 1995,
143, 407 ? 455.
[10] a) A. Mller, B. Botar, S. K. Das, H. Bgge, M. Schmidtmann, A.
Merca, Polyhedron 2004, 23, 2381 ? 2385; b) A. Mller, S. Q. N.
Shah, H. Bgge, M. Schmidtmann, Nature 1999, 397, 48 ? 50.
[11] K. Wassermann, M. H. Dickman, M. T. Pope, Angew. Chem.
1997, 109, 1513 ? 1516; Angew. Chem. Int. Ed. Engl. 1997, 36,
1445 ? 1448.
[12] Examples of recent work include: a) B. S. Bassil, S. Nellutla, U.
Kortz, A. C. Stowe, J. van Tol, N. S. Dalal, B. Keita, L. Nadjo,
Inorg. Chem. 2005, 44, 2659 ? 2665; b) L.-H. Bi, U. Kortz, S.
Nellutla, A. C. Stowe, N. S. Dalal, B. Keita, L. Nadjo, Inorg.
Chem. 2005, 44, 896 ? 903; c) A. C. Stowe, S. Nellutla, N. S. Dalal,
U. Kortz, Eur. J. Inorg. Chem. 2004, 3792 ? 3797; d) D. Jabbour,
B. Keita, I. M. Mbomekalle, L. Nadjo, U. Kortz, Eur. J. Inorg.
Chem. 2004, 2036 ? 2044; e) U. Kortz, S. Nellutla, A. C. Stowe,
N. S. Dalal, U. Rauwald, W. Danquah, D. Ravot, Inorg. Chem.
2004, 43, 2308 ? 2317; f) U. Kortz, S. Nellutla, A. C. Stowe, N. S.
Dalal, J. van Tol, B. S. Bassil, Inorg. Chem. 2004, 43, 144 ? 154.
[13] A. J. Tasiopoulos, A. Vinslava, W. Wernsdorfer, K. A. Abboud,
G. Christou, Angew. Chem. 2004, 116, 2169 ? 2173; Angew.
Chem. Int. Ed. 2004, 43, 2117 ? 2121.
[14] a) R. Sessoli, D. Gatteschi, A. Caneschi, M. A. Novak, Nature
1993, 365, 141 ? 143; b) T. Lis, Acta Crystallogr. Sect. B 1980, 36,
2042 ? 2046.
[15] J. M. Clemente-Juan, E. Coronado, Coord. Chem. Rev. 1999,
193?195, 361 ? 394.
[16] a) L.-H. Bi, U. Kortz, Inorg. Chem. 2004, 43, 7961 ? 7962;
b) T. M. Anderson, W. A. Neiwert, K. I. Hardcastle, C. L. Hill,
Inorg. Chem. 2004, 43, 7353 ? 7358; c) P. Mialane, A. Dolbecq, J.
Marrot, E. Rivire, F. Scheresse, Angew. Chem. 2003, 115,
3647 ? 3650; Angew. Chem. Int. Ed. 2003, 42, 3523 ? 3526; d) J. M.
Clemente-Juan, E. Coronado, J. R. Galn-Mascars, C. J.
Gmez-Garca, Inorg. Chem. 1999, 38, 55 ? 63; e) K. Wassermann, R. Palm, H.-J. Lunk, J. Fuchs, N. Steinfeldt, R. Stsser,
www.angewandte.org
2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3779
Communications
Inorg. Chem. 1995, 34, 5029 ? 5036; f) T. J. R. Weakley, J. Chem.
Soc. Chem. Commun. 1984, 1406 ? 1407.
[17] a) R. Contant, A. Tz, Inorg. Chem. 1985, 24, 4610 ? 4614; b) R.
Contant, Inorg. Synth. 1990, 27, 110.
[18] A cerium-containing derivative of [H7P8W48O184]33 with the
formula [(K)Ce6P8W56O208]21 was recently presented at a
conference. M. T. Pope, International Symposium on Nanostructures and Physicochemical Properties of Polyoxometalate
Superclusters and Related Colloid Particles, Shonan Village
Center, Kanagawa, Japan, 21.-25. November 2004.
[19] Crystal data for K12Li131� H2O: A blue block with dimensions
0.09 0.07 0.06 mm3 was mounted on a glass fiber for indexing
and intensity data collection at 153 K on a Bruker D8 SMART
APEX CCD single-crystal diffractometer using MoKa radiation
(l = 0.71073 ). Of the 9102 unique reflections (2qmax = 56.128),
5826 reflections (Rint = 0.083) were considered observed (I >
2s(I)). Direct methods were used to solve the structure and to
locate the tungsten and copper atoms (SHELXS-97). Then the
3780
2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
remaining atoms were found from successive difference maps
(SHELXL-97). The final cycle of refinement, including the
atomic coordinates, anisotropic thermal parameters (W, Cu, P, K
and Cl atoms), and isotropic thermal parameters (O atoms)
converged at R = 0.068 and Rw = 0.179 (I > 2s(I)). No lithium
ions could be located crystallographically. In the final difference
map the deepest hole was 3.054 e 3 and the highest peak
4.663 e 3. Routine Lorentz and polarization corrections were
applied and an absorption correction was performed using the
SADABS program (G. M. Sheldrick, Siemens Analytical X-ray
Instrument Division, Madison, WI, 1995). Further details on the
crystal structure investigations may be obtained from the
Fachinformationszentrum Karlsruhe, 76344 Eggenstein-Leopoldshafen, Germany (fax: (+ 49) 7247-808-666; e-mail: crysdata@fiz-karlsruhe.de), on quoting the depository number CSD415126.
[20] I. D. Brown, D. Altermatt, Acta Crystallogr. Sect. B 1985, 41,
244 ? 247.
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Angew. Chem. Int. Ed. 2005, 44, 3777 ?3780
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