We report a self-recognition phenomenon based on an assembly process in a homogeneous dilute aqueous solution of two nano-scaled, spherical polyprotic metal oxide-based macroions (neutral species in crystals), also called Keplerates of the type [(linker)₃₀(pentagon)₁₂]≡[{M(H₂O)}₃₀{(Mo)Mo₅}₁₂] where M is Fe(III) or Cr(III). Upon deprotonation of the neutral species, the resulting macroions assemble into hollow "blackberry"-type structures through very slow homogeneous dimer-oligomerization processes. Although the geometrical surface structures of the two macroions are practically identical, mixtures of these form homogeneous superstructures, rather than mixed species. The phase separation is based on the difference in macroionic charge densities present during the slow homogeneous dimer or oligomer formation. The surface water ligands' residence times of Cr(III) and Fe(III) differ markedly and lead to very different interfacial water mobilities between the Keplerates.

The 16-Fe(III)-containing 48-tungsto-8-phosphate [P(8)W(48)O(184)Fe(16)(OH)(28)(H(2)O)(4)](20-) (1) has been synthesised and characterised by IR and ESR spectroscopy, TGA, elemental analyses, electrochemistry and susceptibility measurements. Single-crystal X-ray analyses were carried out on Li(4)K(16)[P(8)W(48)O(184)Fe(16)(OH)(28)(H(2)O)(4)]66 H(2)O2 KCl (LiK-1, orthorhombic space group Pnnm, a=36.3777(9) A, b=13.9708(3) A, c=26.9140(7) A, and Z=2) and on the corresponding mixed sodium-potassium salt Na(9)K(11)[P(8)W(48)O(184)Fe(16)(OH)(28)(H(2)O)(4)].100 H(2)O (NaK-1, monoclinic space group C2/c, a=46.552(4) A, b=20.8239(18) A, c=27.826(2) A, beta=97.141(2) degrees and Z=4). Polyanion 1 contains--in the form of a cyclic arrangement--the unprecedented {Fe(16)(OH)(28)(H(2)O)(4)}(20+) nanocluster, with 16 edge- and corner-sharing FeO(6) octahedra, grafted on the inner surface of the crown-shaped [H(7)P(8)W(48)O(184)](33-) (P(8)W(48)) precursor. The synthesis of 1 was accomplished by reaction of different iron species containing Fe(II) (in presence of O(2)) or Fe(III) ions with the P(8)W(48) anion in aqueous, acidic medium (pH approximately 4), which can be regarded as an assembly process under confined geometries. One fascinating aspect is the possibility to model the uptake and release of iron in ferritin. The electrochemical study of 1, which is stable from pH 1 through 7, offers an interesting example of a highly iron-rich cluster. The reduction wave associated with the Fe(III) centres could not be split in distinct steps independent of the potential scan rate from 2 to 1000 mV s(-1); this is in full agreement with the structure showing that all 16 iron centres are equivalent. Polyanion 1 proved to be efficient for the electrocatalytic reduction of NO(x), including nitrate. Magnetic and variable frequency EPR measurements on 1 suggest that the Fe(III) ions are strongly antiferromagnetically coupled and that the ground state is tentatively spin S=2.

Dedicated to Professor Francis SØcheresse on the occasion of his 60th birthdayPolygons can be placed on spherical surfaces such that periodical structures of a cyclic nature result, while these can be considered as discrete models for two-dimensional (extended) structures. If we wish to construct a chemical structure on a spherical capsule surface in the same way, we have to remember that 1) pentagons are the basic units for sphere constructions, as is well known, for example, from virus structures, 2) they exist, for example, in the form of { ( [5b]). However, until now it was not possible to synthesize a spherical capsule surface directly by the addition of linkers to the pentagonal units that are available in a dynamic library. [1][2][3][4][5] It is significant that in the Keplerates the linkers describe generic Archimedean solids: in the case of dinuclear linkers M 2 a distorted truncated icosahedron, {M 2 } 30 , and in the case of mononuclear linkers the unique icosidodecahedron (Figure 1) [6] {M 30 }, which has-geometrically speaking-linked M 3 triangles. Surprisingly the related consequences for chemistry have not been discussed until now. In the {M 30 } situation, there is a network of corner-shared triangles on the sphere surface, this can result unique magnetic properties as in the case of the "classical" Keplerate {(Mo VI )Mo . [7, 8] This is the first laboratory example of a "zero-dimensional" system that at low temperatures embodies characteristics of geometrical frustration/magnetic ordering [8b] which otherwise have only been observed in selected one-, two-, and three-dimensional lattice spin systems.[9] Herein we report on the spherical cluster 1 a where the twelve {(Mo VI )Mo VI 5 } type units fix 30 d 1 V IV linkers/centers with spin S = 1/2 in the form of an icosidodecahedron, and thus 1) demonstrating for the first time that the spherical capsule/Keplerate can be directly constructed from the mononuclear linkers and the appropriate molybdate library, [5c] 2) providing the chance to obtain new information regarding the unique molecular magnetism of the {M 30 } type network of linkers/triangles, and 3) clarifying the quantum effects of the spin S = 1/2 vanadyl linkers especially in connection with the two-dimensional S = 1/2 KagomØ lattice which contains linked triangles and exhibits unique magnetic properties.[9a]After adding vanadyl sulfate to an acidified molybdate solution, in the presence of K + ions, compound 1 precipitates after some time in high yield. (A simpler expression for the

Dedicated to Professor Peter Day on the occasion of his 70th birthdayIn the field of polyoxometalate chemistry, porous spherical molybdenum oxide-based clusters of the type {(Mo VI )Mo VI 5 } 12 (linker) 30 , [1] called Keplerates, [2a,b] are notable not only from an aesthetic point of view [2c] but also because they show properties of interest for different areas of science. Some of these clusters can act as artificial cells exhibiting gated pores while interacting specifically with their environments; others are of interest for several aspects of materials science. [3][4][5] In detail, of interest are a) solution properties in connection with a new type of assembly process leading to vesicles, including magnetic ones, [6a,b] b) the option to employ the characteristic interactions with amphiphiles for the generation of monolayers and Langmuir-Blodgett films [6c] as well as highly ordered honeycomb nanostructures at airwater interfaces, [6d] c) the integration into sol-gel-derived silica to obtain unprecedented hybrids, [6e] and d) the discovery of novel magnetic properties, [6f]

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