Erich Krickemeyer

Organizational Forms of Matter: An Inorganic Super Fullerene and Keplerate Based on Molybdenum Oxide

Plato and Kepler would have been pleased. Despite the large number of atoms present the cluster anion 1 resembles an icosahedral-type structure. This represents definitively an unprecedented event in chemistry! The structure is made up of 12 {Mo11 } fragments such that the fivefold symmetry axes are retained in the resulting spherical object. As an inscribed icosahedron can be recognized in the spherical shell of 1 (see picture), similarities with Keplers famous shell model of the cosmos can be seen.

“Molecular Symmetry Breakers” Generating Metal‐Oxide‐Based Nanoobject Fragments as Synthons for Complex Structures: [{Mo128Eu4O388H10(H2O)81}2]20−, a Giant‐Cluster Dimer

The synthesis and manipulation of a huge variety of nanoscaled species of similar chemical nature under one-pot reaction conditions requires access to a potential TMdynamic library∫ of appropriate building blocks.[1a] For instance, by exploiting a detailed knowledge of polyoxometalate chemistry, a variety of discrete clusters (see ref. [1b ± g]) and related extended structures[2] can be formed by the linking of welldefined metal ± oxygen building blocks. These types of compounds have been shown to exhibit unusual topological as well as electronic properties and, furthermore, are interesting for materials science.[3±5] A couple of years ago, we reported wheel-shaped mixed-valence molybdenum clusters of the type {Mo154}, {Mo176}, 6, 7] and {Mo248}; of these, the first two parent species–exhibiting nanometer-sized cavities and therefore presenting fascinating perspectives for a new type of host ± guest chemistry–can now be obtained in high yields in facile syntheses.[8] Herein, we describe for the first time a dimer of two giant clusters, that is, of structurally well-defined covalently linked nanoobjects with a rather high degree of complexity. The dimer contains two elliptical molybdenum oxide based units, linked together by two Eu-O-Mo bonds, each unit incorporates 128 MoVI/V and 4 EuIII centers and includes large fragments of the above-mentioned parent clusters. The interpretation would be that these dimers are formed by EuIII centers acting as symmetry breakers which prevent the corresponding highly symmetrical parent-ring closure.[1b, 6] Of general importance is that in systems showing growth, potential (abundant) agents, such as EuIII centers, can act as TMsymmetry breakers∫ which results in the generation of structural complexity. In any case, it is important to realize that large nanoobject fragments can, in principle, be used as synthons. The ability to connect or assemble clusters in a predefined manner may allow the design of nanoscopic devices using the TMbottom up∫ method (that is, generating large objects from small units). While the TMclassical∫ reduction of an acidified aqueous molybdate solution leads to the blue, wheel-shaped tetraand hexadecameric parent-cluster anions mentioned above,[6] the generation of smaller species requires the presence of electrophiles, such as PrIII ions which increase the curvature by replacing the larger electrophilic {Mo2} -type building units (see below). In the presence of smaller EuIII ions, even ring closure to the parent clusters does not take place, which allows the isolation of compound 1 containing a novel cluster collective. Compound 1 was characterized by single-crystal X-ray structure analysis[9] (including bond valence sum (BVS) calculation to aid in the determination of the (formal) number of MoV centers and protonation sites),[10] elemental analyses ((K), Eu, Mo; see details in ref. [12]), thermogravimetric analysis, redox titration (to aid in the determination of the (formal) number of MoV centers), IR, and EXAFS spectroscopy (Eu-LIII edge,[11] with the option to distinguish in principle between the different Eu centers in the lattice and cluster sites) as well as magnetic susceptibility measurements with a SQUID magnetometer.

Materielle Organisationsformen: ein anorganisches Superfulleren und Keplerat auf Molybdänsauerstoffbasis

Da hatten wohl auch Platon und Kepler ihre Freude gehabt! Trotz der grosen Zahl an Atomen weist das Cluster-Anion 1 eine ikosaedrische Struktur auf – sicherlich ein Novum in der Geschichte der Chemie! Es setzt sich derart aus 12 {Mo11}-Fragmenten zusammen, das im resultierenden kugelformigen Gebilde die funfzahligen Drehachsen erhalten bleiben. Da man in 1 ein in eine Kugel einbeschriebenes Ikosaeder erkennen kann, ahnelt dieses Anion strukturell dem beruhmten Keplerschen Schalenmodell des Kosmos (siehe Bild).

Open and shut for guests in molybdenum-oxide-based giant spheres, baskets, and rings containing the pentagon as a common structural element

A novel exchange between ligands and/or guest molecules can be accomplished in giant molecular spheres (an example is shown in the picture) which are in equilibrium with the corresponding giant baskets in solution.

Darstellung und Röntgenstrukturanalyse von 26 Thiomolybdato- bzw. Thiowolframato-und eines Selenowolframato-Komplexes

SummaryThe preparation and characterization by X-ray structure analysis of the following chalcogenometalato complexes are reported: 1: [(Ph3P)2N]2(NEt4)[Fe(WS4)2]·2MeCN; 2: [(Ph3P)2N]2(NEt4)[Cu(WS4)2]·2MeCN; 3: [(Ph3P)2N]2(NEt4)[Ag(MoS4)2]·MeCN; 4: [(Ph3P)2N]2(NEt4)[Ag(WS4)2]·MeCN; 5: (PPh4)2[Hg(WS4)2]; 6: (PPh4)2[Au2(WOS3)2]; 7: (PPh4)4[Pb2(MoS4)4]; 8: (PPh4)4[Pb2(WS4)4]; 9: (NEt4)2[Fe(WS4)2(H2O)2]; 10: [Fe(DMSO)6][Cl2Fe(MoS4)]; 11: [Fe(DMSO)6][Cl2Fe(MoOS3)]; 12: (PPh4)(NMe3CH2Ph)[Cl2Fe(WS4)]; 13: [Fe(DMF)6][Cl2Fe(WS4)]; 14: (PPh4)2[Cl2Fe(WS4)]; 15: (PPh4)2[Cl2Fe(WS4)]·2 CH2Cl2; 16: (PPh4)2[NCCu(MoS4)]; 17: (PPh4)2[NCAg(MoS4)]; 18: (PPh4)2[NCAg(WS4)]; 19: (PPh4)2[Cu3Cl3(MoOS3)]; 20: (PPh4)2[Cu3Br3(MoS4)]·MeCN; 21: (PPh3)3Cu2(MoOS3)·0.8 CH2Cl2; 22: (PPh3)3Cu2(WOS3)·0.8 CH2Cl2; 23: {Cu3MoS3Br}(PPh3)3O·0.5Me2CO; 24: (PPh3)3Ag2(WSe4)·0.8 CH2Cl2; 25: [(Ph3P)2N]2(NEt4)2[Fe2S2(WS4)2]·3MeCN; 26: (PPh4)2[MoO(MoS4)2]; 27: (PPh4)2[Br2Fe(WOS4)]·DMF.

A New Type of Supramolecular Compound: Molybdenum-Oxide-Based Composites Consisting of Magnetic Nanocapsules with Encapsulated Keggin-Ion Electron Reservoirs Cross-Linked to a Two-Dimensional Network

Nanosized metal-oxide-based composites-novel supramolecular entities-have been assembled and even cross-linked under one-pot conditions. The supramolecular entity (see picture) consists of a paramagnetic icosahedral capsule of the type {Mo VI 72 Fe III 30 } as a host which encloses a potential electron-reservoir noncovalently bonded guest, the reduced Keggin cluster [H 2 PMo 12 O 40 ] 3- .

Exchange Interactions and Zero-Field Splittings in C3-Symmetric MnIII6FeIII: Using Molecular Recognition for the Construction of a Series of High Spin Complexes Based on the Triplesalen Ligand

The reaction of the tris(tetradentate) triplesalen ligand H6talen(t-Bu2), which provides three salen-like coordination environments bridged in a meta-phenylene arrangement by a phloroglucinol backbone, with Mn(II) salts under aerobic conditions affords, in situ, the trinuclear Mn(III) triplesalen complexes [(talen(t-Bu2)){Mn(III)(solv)n}3]3+. These can be used as molecular building blocks in the reaction with [Fe(CN)6]3- as a hexaconnector to form the heptanuclear complex [{(talen(t-Bu2)){Mn(III)(solv)n}3}2{Fe(III)(CN)6}]3+ ([Mn(III)6Fe(III)]3+). The regular ligand folding observed in the trinuclear triplesalen complexes preorganizes the three metal ions for the reaction of three facially coordinated nitrogen atoms of a hexacyanometallate and provides a driving force for the formation of the heptanuclear complexes [M(t)6M(c)]n+ (M(t), terminal metal ion of the triplesalen building block; M(c), central metal ion of the hexacyanometallate) by molecular recognition, as has already been demonstrated for the single-molecule magnet [Mn(III)6Cr(III)]3+. [{(talen(t-Bu2))(Mn(III)(MeOH))3}2{Fe(III)(CN)6}][Fe(III)(CN)6] (1) was characterized by single-crystal X-ray diffraction, FTIR, ESI- and MALDI-TOF-MS, Mössbauer spectroscopy, and magnetic measurements. The molecular structure of [Mn(III)6Fe(III)]3+ is overall identical to that of [Mn(III)6Cr(III)]3+ but exhibits a different ligand folding of the Mn(III) salen subunits with a helical distortion. The Mössbauer spectra demonstrate a stronger distortion from octahedral symmetry for the central [Fe(CN)6]3- in comparison to the ionic [Fe(CN)6]3-. At low temperatures in zero magnetic fields, the Mössbauer spectra show magnetic splittings indicative of slow relaxation of the magnetization on the Mössbauer time scale. Variable-temperature-variable-field and mu(eff) versus T magnetic data have been analyzed in detail by full-matrix diagonalization of the appropriate spin-Hamiltonian, consisting of isotropic exchange, zero-field splitting, and Zeeman interaction taking into account the relative orientation of the D tensors. Satisfactory reproduction of the experimental data has been obtained for parameters sets J(Mn-Mn) = -(0.85 +/- 0.15) cm(-1), J(Fe-Mn) = +(0.70 +/- 0.30) cm(-1), and D(Mn) = -(3.0 +/- 0.7) cm(-1). Comparing these values to those of [Mn(III)6Cr(III)]3+ provides insight into why [Mn(III)6Fe(III)]3+ is not a single-molecule magnet.

Linking Icosahedral, Strong Molecular Magnets {Mo} to Layers—A Solid‐State Reaction at Room Temperature

The by no means trivial, solid-state reaction for the condensation of {(Mo)Mo 5 } 12 Fe 30 giant spheres commences through the water ligands and leads to oxo (or hydroxo) bridging. As the discrete icosahedral units approach each other, their oxygen atom bridges ultimately form covalent bonds (Fe-Fe 3.79 A , see picture) to result in a symmetric layered structure.

Giant Ring-Shaped Building Blocks Linked to Form a Layered Cluster Network with Nanosized Channels: [Mo124VIMo28VO429(μ3-O)28H14(H2O)66.5]16−

A novel type of electron-rich (basic!) nanosized channels can be built up by linking giant ring-shaped building blocks, which occur in the layered compound of composition [Mo124VIMo28VO429(μ3-O)28H14(H2O)66.5]16− (see figure). The corresponding sodium salt is obtained by reduction of an acidified aqueous molybdate solution under special reaction conditions.

Unusual Stepwise Assembly and Molecular Growth: [H14Mo37O112]14− and [H3Mo57V6(NO)6O189(H2O)12(MoO)6]21−

The understanding of the formation of complex molecular systems from simple building blocks by conservative self-assembly processes is still a challenge. We report the synthesis and structural characterization of the large reduced polyoxometallate compounds (NH4)(14)[H14Mo37O112]. 35 H2O (1), (NH4)(21)[H3Mo57V6(NO)(6)O-183(H2O)(18)]. 55H(2)O (2) (by an improved synthesis) and Na-3(NH4)(18)[H3Mo63V6(NO)(6)O-195(H2O)(12)]. 41H(2)O (3). The cluster systems are formed by a stepwise growth process. This implies the appearance, during the cluster formation, of ephemeral polyoxometallate intermediates (some of which we were able to isolate). The negative charge and therefore the nucleophilicity of the intermediate cluster fragments increase when they are reduced, resulting in further attraction of electrophiles and thus in growth of molecular systems. IN the case of the cluster anion of 3 we observed, correspondingly, the loss of an [MoO](4+) oxometallate fragment by air oxidation; this implies that aits uptake and release are controlled by th degree of reduction of the cluster. correspondingly, intermediates between the anions of 2 and 3 of the {Mo57+xV6} type could be isolated. The unusual anion of 1 is formed by symmetry breaking processed.