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An Unusual Polyoxomolybdate Giant Wheels Linked to Chains.

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Angew. Chem. Int. Ed. Engl. 1997,36, No. 5
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Weinheim, 1997
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An Unusual Polyoxomolybdate:
Giant Wheels Linked to Chains**
Achim Miiller," Erich Krickemeyer, Hartmut Bogge,
Marc Schmidtmann, Frank Peters, Carsten Menke,
and Jochen Meyer
Dedicated to Professor Gotlfried Huttner
on the occasion of his 60th birthday
Complex systems in biology are built up in a stepwise manner
through a sequence of programmed chemical processes. The
chemist is in a position to connect elementary building blocks
and their derivatives in different ways, enabling him to synthesize a large variety of important and remarkable substances.
Of particular interest in this context are the simple anionic
species of the type EOr- (E = elements of the p and d block in
high oxidation states), which also play an important role beyond the domain of the chemist and his
example in the geosphere (silicates) and biosphere (diatoms).
We have employed the above-mentioned reaction types and previously succeeded in isolating compounds with discrete structures that themselves have a molecular size and mass of the
order of proteins.r31We have now succeeded in taking the next
step on a promising pathway: the linking of such giant particles.
The blue, mixed-valence (type I11 according to Robin and
was isolated by a stepwise
Day) diamagnetic compound lr6,''
reduction of a hydrochloric acid solution containing poly-
Figure 1. Polyhedral representation of a selected chain in 1 and ball-and-stick representation of the linking types (the linking centers are identical with the crystallographic inversion centers). Color coding of the polyhedra: Mo octahedra: blue;
pentagonal bipyramids in the centers of the {Mag} units: turquoise; {Mo,}'+
yellow; {Mo,}-type linking units: red.
groups linking the { M o ~ units:
molybdate ions in the presence of sodium ions. The preparation
yields well-formed, triclinic crystals of 1, as well as a fraction of
poorly crystalline material (for further discussion of this problem see ref. [3 b]). The compound was characterized by spectroscopic methods (Vis/NIR, IR, Raman, and ESR spectroscopy),
elemental analyses (also of single crystals), and manganometric
redox titration as well as by X-ray crystallography.r61(For details of error limits see below and ref. [7]).
The rather intricate single-crystal X-ray structure analysis[6]
revealed that the characteristic structural features of 1 are chains
of linked rings (Figure I), which resemble, apart from defects
in 1, the recently published compound 2 (Figure 2). Thus, the
+ 5 [Mo 1s4"O)
1 ~ ~ 4 * 0 ( ~ ~ ~ 2,ca.350
* ~ ~ ~ ~ ~ 2, 0 1
triclinic unit cell of 1 contains two crystallographically different
ring-shaped (MO,,,O,~,(OH),,(H,O),,)
building units, which
occupy two inversion centers. The structural similarities that
they possess are discussed as follows: Two neighboring rings are
formally linked (at (H,O) Mo=O positions of 2) by four Mo-OMo groups through a type of condensation process (cf. Figure 2). The similarity of the ring-shaped building units in 1 and
2 is particularly significant above all with respect to the presence
of 14 {Mo,} basic fragments in each case, which also appear in
numerous related giant cluster^.^^ 51 In addition, the OH
groups and the reduced Mo centers are at the same position in
Figure 2. Comparison of the rings in 1 (left) and 2 (right). Top: Complete rings;
bottom: View of only the upper half of each ring to clarify the positions of the
missing {Mo,} units in 1. These missing {Mo,} groups in 1 lie at the positions
indicated by arrows and correspond to the hatched yellow polyhedra in 2. The
relevant Mo positions in 1 that are involved in bridges possess a (H,O)Mo=O
function in 2. The hatched position in 1 is occupied up to about 50% with an (Mo2}
group (color coding as in Figure 1).
Prof. Dr. A. Muller. E. Krickemeyer, Dr. H. Bogge, M. Schmidtmann,
Dip1.-Chem. F. Peters, Dip1.-Chem. C. Menke, DipLChem. J. Meyer
Fdkultit fur Chemie der Universitit
Lehrstuhl fur Anorganische Chemie I
Postfach 100131, D-33501 Bielefeld (Germany)
Fax: Int. code +(S21) 106-6003
e-mail: amueller(a
We wish to thank Prof. Dr. G. M. Sheldrick (Universitat Gottingen, Germany)
for allowing us to use the unpublished program SHELXS-96.
0 VCH Veria~sgesellschafimbH, 0-69451
both compounds 1 and 2.[3a1
In 2 the (Mo,) units above and
below the equator of the ring are each connected through
seven (in total 14) {(H,O)O,MO-O-MOO,(H,O))~+ units
(-{MO,}~+), which are positioned at the upper and lower
edges of the central cavity resulting in an approximate D,, symm e t r ~ . [As
~ ' shown in the bottom of Figure 2 (marked by arrows), a total of five of these connecting units are missing at certain positions in 1. This correlates with the observation that the rings in 1 are somewhat compressed at these
0570-0833,'97!3605-0484 $ 15.00+ .2S/0
Angr". Chem. Inr. Ed. Engl. 1997, 36, N o . 5
positions and thereby possess an ellipsoidal appearance. Formally, the following structure or construction principle emerges
for the rings in 2 and 1, respectively: 14 {Mas} units are linked
through 14 {Mo,} and 14 - x {Mo,} groups ({Mo,,,}
({Mo,,~} in 1) = [I4 {Mo,} + I 4 {Mo,}] + I 4 {Mo2} (partially occupied in 1)). This corresponds to the formula
~ M o V ' ~ 0 ~ ( H 2 0 ~ ~ } 1 4 - ~ { M o ~ 0 ~ 6 ( 0 H ~ ~ ~ H 2 0 ~ 3 } ~ 4 (' = 5 k for
1). The {Moll units refer to the Mo centers that link the {Mo,}
fragments in the equatorial plane (see Figure 2 and ref. [3a]).
An essential difference between the preparation of 2 and 1, is
that elemental iron was used instead of NH,OH.HCI as the
reducing agent in 1. Since under the chosen reaction conditions
(low pH values), species exist with the above-mentioned {Mo,}
fragrnents.[j. which possess a pentagonal bipyramid of the
type Mo(NO)06 (or MOO,) in their center, the replacement of
+ 1 leads to a lower
{ONMoJ3+fragments of 2 by { O M O } ~in
negative charge on the intermediate products in solution (cf.
refs. [3 - 51). Current knowledge suggests that a lower charge
density not only facilitates a further condensation, but also leads
to a lower nucleophilicity and consequently to a lower occupation of the {Mo,} positions. This is evidently essential for the
formation of 1. Therefore, it is basically possible to control the
relevant connectivity (and consequently the cluster size) through
changes in pH value and reduction state (or charge density). An
increase in the H + ion concentration favors condensation,
whereas an increasing charge density has the opposite effect.
This assertion is valid for the relevant range of H i and MoV/
Mo"' concentrations. The final product at high H + concentration, when no reducing agent is present, is Mo03.2H,0, which
shows certain structural similarities to 1 and 2, that is, coordinated and noncoordinated H,O molecules.[g1In this context it is
interesting to note that a "molybdenum blue" solution contains
species that correspond to hydrated and protonated molecular
(polynuclear) molybdenum trioxide with the approximate composition (MoO,),(H,O),H, and in particular with basic ringshaped structures (see ref. [4]). The structural differences between the rings in 1 and 2 are so insignificant that they are only
marginally reflected in their IR (i.e. by a characteristic band at
about 750 cm- ') and Vis/NIR spectra. In the case of the IR
spectrum, this is a consequence of the weakly coupled vibrations
located mainly in units that are terminated by heavy Mo
These investigations substantiate our view expressed in the
introduction that one can anticipate further important results in
the area of polyanion and polycation chemistry with respect to
aspects of structural chemistry and materials research (cf. zeolite
research1Io1).Here, in 1, for example, chains exist that are built
up from electron storage units! This reaffirms that a type of
organization principle[' b1 is operating that is based on the high
formation tendency of {Mas} fragments and their ability to link
together in different w a y ~ . [ ~ * ~ ]
It is especially remarkable that oxide phases with the previously mentioned structural variety are found not only at the
molecular level but also in macroscopic forms. This is shown
quite impressively by the "artistic" structures that are formed
from ten thousand different types of diatoms which have eukaryontic cells. In the diatoms, the connection of XO, units
occurs under dissipative conditions, that means under entropy
export in an open system." 'I Now the central question arises,
whether it is possible, under dissipative conditions, to create
similar macroscopic metastable structures formed from other
EO, basic units (dissipative self-organization leading to a stationary nonequilibrium state[I3]). In any case, it can be presumed that with a knowledge of the intrinsic features of the
investigated reaction system, coupled with the relevant choice of
1n1.Ed En,?/. 1997, 36, No. 5
special reaction conditions, a huge variety of novel molecular
structures with high complexity and rnultif~nctionality['~~
be created, based on conservative processes in the area of polyoxoanion chemistry.
Experimental Section
1: A solution of Na,Mo04.2H,0 ( p a . ) (50 g, 206.7 mmol) in H,O (450 mL) in a
500 mL Erlenmeyer flask was adjusted with stirring to a pH value of about 0.8 with
3 2 % hydrochloric acid (p.a.). After addition of iron powder (500 mg, 9 mmol)
(Merck; 150 pm) the mixture was left to stand at 20°C (hydrogen evolution) in a
flask covered with a watch glass. After 24 h, a further 500 mg of iron powder was
added to the deep-blue reaction mixture which was allowed to stand without further
disturbance (to improve the formation of crystals). After 5 to 6 weeks of 1 was
separated with a glass frit under an argon atmosphere, and dried in an argon
atmosphere over calcium chloride. Yield: 10.5 g (27.4% based on Mo). Compound
1 also forms in a shorter time at a higher temperature but precipitates without a
significant crystalline fraction. Characterization of 1: IR (KBr disk, under argon.
some characteristic bands): ^v[cm-'] =1614 (m. 6(H,O)). ca. 995 (sh). 972 (m),
911 (w-m) (v(Mo=O)), ca. 810 (sh), 746 (s), 713 (m). 633 (s). 557 (s). Vis/NIR
(degassed H,O; adjusted to pH 1.5 with HCI, the structure of 1 in solution is
unknown, but the number of MoV centers is the same as in the solid 1, see [7]):
i.[nm] (eM[105L m o l - ' cm-'1) =745 (l.?, intervalence charge transfer (IVCT)),
1060 (1.4, IVCT) (hands in degassed methanol: 745 and 1045 nm); for additional
control solid-state VisINIR spectrum (KBr pellet in transmission): = 750 and
= 1080. The e value, which is dependent on the numbers of Mo" centers. can he
interpreted in solution upon chain cleavage.
Received: September 20. 1996 [Z9574IE]
German version: Angeu. Chem. 1997, 109, 500-502
Keywords: clusters * macrocycles
oxometalates supramolecular chemistry
[l] a) A. F. Wells, Structural Inorganic Chemistry, 5th ed.. Clarendon, Oxford,
1984; H. J. Rosler, Lehrbuch der Mineralogie, 3rd ed., Deutscher Verlag fur
Grundstoffindnstrie, Leipzig. 1984; M. T. Pope, A. Miiller. Angew. Chem.
1991, 103, 56; Angew. Chem. Int. Ed. Engl. 1991. 30, 34; A. Miiller, Nature
1991, 352, 115; From Platonic Solids to Anti-Retroviral Actnrty. (Eds.: M. T.
Pope. A. Miiller), Kluwer, Dordrecht, 1994; M. I. Khan. J. Znhieta. Prop.
Inorg. Chem. 1995,43, 1-149; A. Miiller, C. Beugholt. Naturr 1996,383,296;
h) A. Miiller. H. Renter, S. Dillinger, Anpew. Chem. 1995, /07, 2505; Angew.
Chem. Int. Ed. Engl. 1995, 34, 2328.
[2] J.-P. Jolivet. M. Henry, J. Livage, De lasolution u l'oxyde, InterEditionsl CNRS
Editions, Paris, 1994.
[3] a) A. Miiller, E. Krickemeyer, J. Meyer, H. Bogge, F. Peters, W Plass, E.
Diemann. S. Dillinger, F. Nonnenbruch, M. Randerath, C. Menke, Anpew.
Chem. 1995, 107, 2293; Angew. Chem. I n t . Ed. Engl. 1995, 34, 2122; b) A.
Miiller, E. Diemann. B. Hollmann, H. Ratajczak, Naturi~,i.rsenschaften1996,
83, 321.
[4] A. Miiller, J. Meyer, E. Krickemeyer, E. Diemann, Angeii. C'lirm. 1996, 108.
1296; Angew. Chem. Int. Ed. Engl. 1996, 35, 1206.
[5] A. Miiller, E. Krickemeyer, S. Dillinger, H. Bogge, W. Plass. A. Proust, L.
Dloczik. C. Menke, J. Meyer, R. Rohlfing, Z. Anorg. A l p . Chem. 1994, 620,
599; A. Miiller, W. Plass. E. Krickemeyer, S. Dillinger. H. Bogge, A. Armatage,
A. Proust, C. Beugholt, U . Bergmann, Angeu. Cliem. 1994, 106, 897; Angeu.
Chrm. Int. Ed. Engl. 1994, 33, 849; A. Miiller, W. Plass, E. Krickemeyer, S.
Dillinger, H. Bogge, A. Armatage, C. Beugholt, U. Bergmann, Monatsh.
Chem. 1994,125,525; A. Miiller, H. Bogge, E. Krickemeyer. S Dillinger. Bull.
Pol. Acad. Sci. (Chem.) 1994, 42, 291.
[6] 1: space group P f ; a = 2540.9(7), h = 3415.3(8), c = 4510.2(14)pm, x =
=100.59(2)', V = 38429118) x 10" pm3 ( p = 23.9
91.28(2), 0 = 92.14(2). -;
cm- I ) ; Z = 2; solution with direct methods, R = 0.124 for 39487 independent
reflections (F,>4u(FO));Siemens R3m/V diffractometer Mo,, radiation,
graphite monochromator. Because of the long time required for data collection, the deep blue crystals of 1 were mounted in oil when removed from the
mother liquor. and the measurement was conducted at - 70 C. The measurements of other individual crystals gave the same results. The data set was
measured to a 20 value of 39". The structure was solved by using the program
SHELXS-96, and refined with the program SHELXL-93. A comparison of
the structnres of 1 and 2 showed that at the corresponding positions where
electronically shielded reduced M o centers (which means MONOgroups) occur
in 2 [3,5], M = O groups with Mo"' centers are incorporated into 1 In addition,
the distribution of the other reduced M o centers as well as H,O and OH ligands
is practically identical in 1and 2. Furthermore, a symmetric O==Mo-0-Mo(H,O)-(H,O)Mo-0-Mo=O
disorder is found at the linking positions in the
rings in 1. Our interpretation of this disorder is chemically motivated, as the
observed distribution of the electron density could in principle be crystallo-
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graphically interpreted by the existence of HO-Mo-0-Mo-OH
units. Our
elucidation is supported by the fact that we could explain the previously mentioned disorder in related structures that show an analogous type of linking. In
addition, the comparable O=Mo-H,O-/H,O-Mo=O
disorder is found in
numerous other (also mononuclear) compounds. Furthermore, all molybdenum atoms with two (trans positioned) or three non-bridging oxygen ligands
(52 in total) possess a coordinated H,O ligand. The sodium atoms are disordered to the extent that it was not possible to determine all of their positions.
Therefore, several sodium analyses were carried out. The detection of a somewhat higher Na value than expected from the given formula for 1 correlated
with the discovery of chloride in the elemental analysis (about 0.4% CI corresponding to ahout 0.4% Na excess). The presence of ahout 1000 atoms in the
asymmetric unit of 1 could indicate that we are dealing here with one of the
most complicated inorganic structures. The figures were prepared with the
program DIAMOND ("Diamond, Informationssystem fur Kristallstrukturen" by Dr. K. Brandenburg, Universitat Bonn, Germany). Further details
of the crystal structure investigation may be obtained from the Fachinformationszentrum Karlsruhe, D-76344 Eggenstein-Leopoldshafen (Germany). on
quoting the depository number CSD-406337.
Due to the size of the system, the complexity of the structure, the quality of the
measurement and the crystals, and the disorder in the system, it is reasonable
to expect that the given formula has an error limit. The number of oxygen (409)
and molybdenum (144) atoms, have-in agreement with the disorder--error
limits of f5 and 2, respectively. The related value for the anion charge is
15 i3 (see also ref. 161). The results of the manganometric titration and the
extinction coefficient of the IVCT band at higher energy of the type
Mo" -* Mo'lshow in 1 as in 2 (without consideration of the electronically inert
MONO groups) that 33 i3 molybdenum centers are according to the present
study (formally) reduced. These are distributed as in 2 (cf. ref. [3]), and thus
only the {Mo,} and {Mo8}groups are involved in the related electron delocalization IS]. The number of delocalized electrons (in the 4d pseudo band) is
33 k 3 . also practically in agreement with the given charge of the anion of 2, at
the lower limit of error (20- [3a], which corresponds to the more realistic
The mixed-valence compound 1 features a small phase range with respect to the
stoichiometry, a phenomenon which is certainly more common in metal
chalcogenide solid-state structures than is frequently assumed (". .progress is
still blocked by a slavish devotion to the cult of the molecule and a naive faith
in the general applicability of Dalton's laws ofchemical combination.": N. N.
Greenwood, Ionic Crjstals, Lattice Defects, and Nonstoichiometry, Butterworths, London, 1968, p. 5). This type of compound, however, is found especiallv freauentlv in mixed-valence transition metal chalcoeenides. which. mecisely because of this feature, also exhibit important physical features like
superconductivity (Mi-xed Valencj Systems Applications in Chemistry, Physics
and Biology, (Ed.: K . Prdssides), Kluwer, Dordrecht, 1991). Interestingly, the
anion of 1 shows the composition of the hydrogen-molybdenum bronzes
H,MoO, (see A. F. Wells. ref. [la], pp. 617-618) that demonstrate conductor
as well as storage properties of electrons and protons (for general aspects see
also Low-Dimensional Electronic Properties of Molybdenum Bronzes and Oxides, (Ed.: C. Schlenker), Kluwer, Dordrecht, 1989).
[9] See for example: Holleman- Wiberg: Lehrbuch der Anorganischen Chemie,
101 st ed.. de Gruyter, Berlin, 1995, pp. 1462-1463.
[lo] P. Ball, Designing the Molecular World. Princeton University Press, Princeton.
1994, pp. 66-73; Y. Izumi, K. Urabe, M. Onaka, Zeolite, Clay, andHeteropoly
Acid in Organic Reactions, VCH, Weinheim, 1992.
[ l l ] S . Mann, G. A. Ozin, Nature 1996, 382, 313.
[12] See also Biomimetic Materials Chemistry, (Ed.: S . Mann), VCH. New York,
1131 G. Nicolis, 1. Prigogine, Exploring Complexity, Freeman, New York, 1989.
[14] Compound 2 shows interesting catalytic behavior as in its presence. novel
carbon cages are formed (Sir H. Kroto, private communication).
Unprecedented Layered Structure of a Fulleride:
Synthesis, Structure, and Magnetic Properties
of a Potassium-Containing Salt
with a CzG Counterion**
Thomas F. Fader,* Annette Spiekermann,
Michael E. Spahr, and Reinhard Nesper
Dedicated to Professor Hans Georg von Schnering
on the occasion of his 66th birthday
Since the discovery of superconductivity[" and ferromagnetism['] in alkali metal (A) fullerides of the type A,C,, ,I3' 41
there has been considerable interest in the magnetic and structural properties of compounds containing C& anions ( n = 16). Although many intercalation compounds have been synthesized, they are frequently polycrystalline powders with anions in
a statistical orientational disorder.[3. - 7 1
Knowledge of the molecular structure of C,, anions and their
mutual interaction is especially important for understanding the
physical properties of these intercalation compounds.[*,91 Symmetry-lowering vibrations and intermolecular interactions of
the fulleride molecules have been discussed within the framework of an electron-phonon mechanism of superconductivity.['0-'21 The threefold degeneracy of the LUMO in MO models of C,, allows degenerate ground states for the anions['41
leading to lower symmetries for these molecules.['51 Although
C;, and Ci; display the expected paramagnetic properties,['
'7 , "1
the nature of the ground state in C& is contr~versial.[~~
We recently reported the high-yield syntheses and structures
of [K([2.2.2]crypt)]salts["] of the paramagnetic trianions of the
heavier carbon homologues E;- (E = Ge, Sn, Pb).r201An attempt to synthesize and crystallize the trianion of C,, resulted
in the isolation of [K([2.2.2]crypt)],C6, (1) as transparent, red,
rhombic crystals [Eq. (a)]. To our knowledge, only one other
crystal structure determination of a compound with ordered
dianions, (PPN)lC&, has been reported.['*] However, the
fullerene molecules in this compound are completly separated
by the cations. Here we report the structure and the magnetic
properties of a novel alkali metal fulleride salt containing alternating layers of ordered C;; anions and [K([2.2.2]crypt)]+
The results of a single crystal structure determination of 1 at
room temperature were consistent with the space group C ~ / C . [ ~ ' ]
However, only one [K([2.2.2]crypt)]moiety could be localized in
the asymmetric unit of the unit cell. An investigation of the
crystals at lower temperatures showed an increase in intensity
for many weak reflections. Using the data collected at 113 K, we
were able to identify fragments of a fullerene molecule in the
difference Fourier map in addition to the [K([2.2.2]crypt)] unit.
Further refinement with a localized model for C,, was possible
in the acentric space group Cc. Two [K([2.2.2]crypt)] units were
observed for each C,, molecule (Figure la). The coordination
0 VCH Verlagsgesellschaft mbH, 0-69451
Weinheim, 1997
Dr. T. F. Fassler, A. Spiekermann, M. E. Spahr, Prof. R. Nesper
Laboratorium fur Anorganische Chemie
der Eidgenossischen Technischen Hochschule
Universitatstrasse 6. CH-8092 Zurich (Switzerland)
Fax: Int. code +(1)632-1149
This work was supported by the ETH Zurich. We are grateful to H.-J. Muhr.
Dr. M. Worle, and Prof. L. Venanzi for valuable discussions.
R 15.00+ .25,'0
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chains, giants, polyoxomolybdate, wheel, unusual, linked
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