Emmanuel Cadot

Molecular weights of cyclic and hollow clusters measured by DOSY NMR spectroscopy.

The Stokes-Einstein expression of the diffusion coefficient as a function of the hydrodynamic radius of the diffusing object does not explicitly carry the mass dependency of the object. It is possible to correlate the translational self-diffusion coefficients D with the molecular weight M for an ensemble of cyclic or hollow clusters ranging from about 200 to 30,000 g x mol(-1). From this correlation, the mass of a cluster can be deduced from its diffusion coefficient. Consistency of diffusion as a power law of mass and Stokes-Einstein formulation is completely fulfilled with the selected compounds of this contribution.

[Mo12S12O12(OH)12(H2O)6]: A Cyclic Molecular Cluster Based on the [Mo2S2O2]2+ Building Block

The pH-dependent self-condensation of the [Mo2 S2 O2 ]2+ complex fragment gives the wheellike Mo12 cluster depicted on the right (ball-and-stick model; large balls: S, medium balls: O, small balls: Mo). Applying this synthetic strategy to other starting materials could provide access to other polyoxothiometalates with well-defined cavities.

Cubic Box versus Spheroidal Capsule Built from Defect and Intact Pentagonal Units

The high-nuclearity polyoxothiomolybdate [H(8)Mo(84)S(48)O(188)(H(2)O)(12)(CH(3)COO)(24)](32-) has been prepared and characterized by single-crystal X-ray crystallography and (1)H NMR, IR, Raman, and UV-vis spectroscopy. The solid-state structure reveals an unprecedented and intriguing arrangement consisting of a nanoscaled anionic cube. The surprisingly open structure of this {Mo(84)}-type cubic box features a large inner void that is accessible via its six open square faces with diameters of ca. 9 Å. Importantly, this molecular system appears to be highly functionalizable because of the presence of 24 exposed exchangeable acetate ligands.

Softening of Pore and Interior Properties of a Metal‐Oxide‐Based Capsule: Substituting 60 Oxide by 60 Sulfide Ligands

The discovery of fullerenes has induced considerable interest in spherical molecular clusters, see for example Refs. [2–5]. Among fullerene-like molecules, spherical watersoluble metal-oxide-based nanocapsules of the type {(M)M5}12(linker)30 (M = Mo or W), belonging to the family of Keplerates, 6] show quite attractive features in the context of nanoand materials science, especially in confined scenarios. Correspondingly, they have been the focus of reviews 11] and highlights, including some in recent textbooks. The nanocapsules contain 12 metal-oxide-based pentagonal units linked by either mononuclear (e.g. Fe, Cr or VO) or dinuclear ({Mo2O4} ) spacers and 20 pores/ channels. 11] In case of the Mo132-type cluster, the interiors of the capsules can be fine-tuned by changing the internal ligands coordinated to the {Mo2O4} linkers. Most importantly, the above-mentioned Keplerates can interact specifically with their environment. Especially the crown ethertype {Mo9O9} pores can react through hydrogen bonding with organic cations (like the guanidinium, amidinium, or protonated urea type), as well as with hydrated metal ions, whereby all act as plugs leading to the closing of the capsules. The 20 smaller {M3M’3O6} pores of the negatively charged M72M’30-type Keplerates (M = Mo , W; M’= V, Fe) have a high affinity for K and NH4 + ions similar to 18crown-6 receptors; this corresponds to sphere surface supramolecular chemistry. The present type of Keplerates also has the potential for being used as nanoreactors. Replacement of the bridging oxo ligands of the abovementioned {Mo2O4} linkers by softer sulfido ligands provides a new option to change the properties/reactivities of Mo132and W72Mo60-type capsules. This change of linkers has now been achieved: We report here the synthesis, crystal structure, and spectroscopic characterization of W72Mo60-type capsules with {Mo2O2(m-S)2(L)} linkers (L = CH3COO ). The important result is that the pore sizes and reactivities/flexibilities as well as the interior capsule properties—also in context of an increase in the internal shell polarizability—are changed by substituting 60 oxide atoms of the known Keplerate containing {Mo2O4} linkers by 60 sulfide atoms; this has, for example, consequences for ligand and cation uptake/release processes as well of course as for the structure of encapsulated species. The synthesis process follows that of previously reported mixed metal Keplerates where the basic {(M)M5}-type units (M = Mo, W) form in solution according to the principles of “Constitutional Dynamic Chemistry” of Lehn while finally 12 of the units get appropriately linked when cations, like {Mo2O4(aq)} , VO(aq), or Fe(aq) [15b] are added to a dynamic library of molybdates and tungstates. In the present case, an aqueous solution of the new dinuclear linker {Mo2O2(m-S)2(aq)} —prepared by hydrolysis of the oxo/thio compound usually used as a source of {Mo2O2(m-S)2} —allowed to obtain the watersoluble Keplerate-type compound 1 (which allows future reactivity studies in solution) as starting material for the less soluble compound 2*** which was isolated by “recrystallization” of the nonrecrystallized 1 in the presence of cobalt (II) ions to get suitable crystals (for details see the Experimental Section). Whereas compound 1 could be only partially characterized because of the poor crystal quality (for the “approximate” formula see Experimental Section), this was not the case for compound 2 which is the focus of our present work. Compound 2, which crystallizes in the space group Immm, was fully characterized by elemental analysis, [*] C. Sch ffer, Dr. A. M. Todea, Dr. H. Bçgge, Prof. Dr. A. M ller Fakult t f r Chemie, Universit t Bielefeld Postfach 100131, 33501 Bielefeld (Germany) E-mail: a.mueller@uni-bielefeld.de Homepage: http://www.uni-bielefeld.de/chemie/ac1/

Cyclic molecular materials based on [M2O2S2]2+ cores (M = Mo or W).

The purpose of this article is to illustrate how conventional precursors can serve, when used with a drop of imagination, to the synthesis of sophisticated inorganic rings and wheels. The self-condensation of the [M2O2S2]2+ fragments under acido-basic process produces, in the presence or absence of guest species, linear enchainment restricted to discrete cyclic entities. This approach was revealed to be a highly fruitful strategy for developing an extended family of compounds, differing in their nuclearity, size and shape, and the nature of the encapsulated guest molecule. Indeed, the resulting cycles delimit a cationic open cavity, which can be filled by neutral polar molecules such as aquo ligands or anionic molecules such as phosphates, polycarboxylates and even metalates. The flexibility of the rings is at the origin of interesting host-guest properties: the deformation (symmetry) and the adaptation (nuclearity) of the inorganic cycle are directly related to the size and the coordination requirements of the encapsulated substrate. The versatility of the metal coordination, octahedral or square pyramidal, confers dynamic properties to the ring. In the solid state, molecular rings assemble in striking 3-D networks based on direct cation-anion connections. Alkali cations are arranged in pillars or layers for anchoring the anionic rings.

Cyclic Ti9 Keggin Trimers with Tetrahedral (PO4) or Octahedral (TiO6) Capping Groups

We have synthesized the cyclic Ti 9 Keggin trimers [(alpha-Ti 3PW 9O 38) 3(PO 4)] (18-) ( 1) and [(alpha-Ti 3SiW 9O 37OH) 3(TiO 3(OH 2) 3)] (17-) ( 2), which are both composed of three (Ti 3XW 9O 37) units (X = P or Si) linked via three Ti-O-Ti bridges and a capping group, which is either tetrahedral PO 4 ( 1) or octahedral TiO 6 ( 2). Polyanions 1 and 2 were fully characterized in the solid state (IR, X-ray diffraction, thermogravimetric and elemental analyses) and in solution ( (31)P or (183)W NMR).

Self-Condensation of [MoV2O2S2]2+ with Phosphate or Arsenate Ions by Acid–Base Processes in Aqueous Solution: Syntheses, Crystal Structures, and Reactivity of [(HXO4)4Mo6S6O6(OH)3]5−, X=P, As

A promising route to new functionalized compounds could be provided by two new heteropolyoxothio anions resulting from self−condensation of the [Mo2S2O2]2+ building unit with arsenate or phosphate ions. There is 31P NMR evidence (illustrated) that the three peripheral PO4 or AsO4 groups in the products are labile.

Evidence of ionic liquid crystal properties for a DODA+ salt of the keplerate [Mo132O372(CH3COO)30(H2O)72]42−

Thermal studies of a DODA+ salt of the nanoscopic hollow sphere [Mo132O372(H2O)72(CH3CO2)30]42− revealed ionic liquid crystalline properties, which were evidenced by Polarised Optical Microscopy, DSC and SA-XRD.

Synthesis, X-ray and Neutron Diffraction Characterization, and Ionic Conduction Properties of a New Oxothiomolybdate Li3[Mo8S8O8(OH)8{HWO5(H2O)}]⋅18 H2O

The new oxothiomolybdate anion [Mo 8 S 8 O 8 (OH) 8 {HWO 5 (H 2 O)}] 3 - (denoted HMo 8 W 3 - ) has been synthesized in aqueous solution by an acido-basic condensation reaction. Four {Mo v 2 S 2 O 2 } building blocks are connected through hydroxo bridges around a central {W v 1 O 6 } octahedron. X-ray and neutron diffraction studies have been performed on single crystals of the lithium salt Li 3 [Mo 8 S 8 O 8 (OH) 8 (HWO 5 - (H 2 O)}] 18H 2 O, (Li 3 HMo 8 W . 18H 2 O) grown from HMo 8 W 3 - in an aqueous solution of LiCl (1 m ). The neutron diffraction experiment enabled us to locate both the protons and the lithium ions. In the structure of Li 3 HMo 8 W. 18H 2 O, ring-shaped anions interleaved by a cluster of disordered hydrogen-bonded water molecules stack on top of each other along lithium pillars. The lithium columns are formed by alternating edge-sharing octahedra and tetrahedra, with one lithium site in four being totally vacant. Ionic conductivity measurements on pressed pellets have shown that Li 3 HMo 8 W . 18H 2 O is a good ionic conductor at room temperature (a= 10 - 5 Scm - 1 ), but the ionic conductivity on single crystals is smaller by two orders of magnitude and is isotropic; this suggests the main path of conduction involves surface protons rather than lithium ions of the bulk.

One-step synthesis and stabilization of gold nanoparticles in water with the simple oxothiometalate Na2[Mo3(μ3-S)(μ-S)3(Hnta)3]

Na2[Mo3(μ3-S)(μ-S)3(Hnta)3] serves both as a reducing and a capping agent in the synthesis of Au nanoparticles in water at room temperature in a “fully green chemistry-type process”, thus avoiding the usual two-step preparation of thiolate-monolayer-coated gold nanoparticles. The nanoparticles were characterized by TEM, DLS, UV-vis spectroscopy, XPS and XRD analyses and cyclic voltammetry.