Christoph Kuhlmann

A variety of combinatorially linkable units as disposition: from a giant icosahedral Keplerate to multi-functional metal-oxide based network structures

In polyoxometalate chemistry a large variety of compounds, clusters and solid-state structures can be formed by linking together metal–oxygen building blocks. Interestingly, reactions based on libraries of virtual building blocks can be planned under appropriate conditions, resulting for instance in the high-yield synthesis of inorganic superfullerenes and giant ring-shaped, electron-rich, mixed-valence polyoxomolybdates with nanosized cavities. The latter species can continue to grow and also can be covalently linked together to form chains as well as layered mesoporous compounds with properties relevant for materials science. The largest polyoxometalate cluster obtained on the basis of such a growth process consists of 248 Mo atoms. Remarkably, such giant ring species can also act as hosts for other clusters forming new types of supramolecular compounds.

MoV2O42+ Directs the Formation and Subsequent Linking of Potential Building Blocks under Different Boundary Conditions: A Related Set of Novel Cyclic Polyoxomolybdates

dThe synthesis and structural characterization of a novel series of deep-red mixed-valence (Mo-VI/Mo-V) compounds with nano-sized spherically shaped cluster anions containing 18, 40, or 54 Mo atoms, respectively, is reported: Na-10-[H4Mo18O56(CH3COO)(2)] x ca. 36 H2O x 3 CH3COOH (1), (NH4)(12)Na-12[Mo40O128] x ca. 70 H2O (2), (NH4)(12)Na-20[H-4-Mo54O168(CH3COO)(4)] x ca. 64 H2O (3), Na-32[H4Mo54O168(CH3COO)(4)] x ca. 128 H2O (4), and Na-32[H4Mo54O168(CH3COO)(4)] x ca. 98 H2O (S). Clusters 3, 4, and 5 differ in the packing of the rings in the lattice. The anions are easily formed by reduction of an acidified aqueous molybdate solution while the deliberately generated (MO2O42+)-O-V group - abundant in all clusters - has a directing influence on the formation of the preliminary building blocks. Furthermore, it is possible to control the ratio of the {Mo-2(V)} units to the Mo-VI centres by adjusting the specific concentration of the employed reducing agent.

On the option of generating novel type surfaces with multiphilic ligands within the cavity of a giant metal–oxide based wheel type cluster: chemical reactions with well-defined nanoobjects

The reaction of an aqueous solution of sodium molybdate with cysteine hydrochloride acting as educt and reducing agent at rather low pH values (≈1.5) results in the formation of Na3[Mo154O462H14(H2 O)48(HO2C–(NH3+)HC –CH2–S–S–CH2–CH(NH 3+)–COO−)11] ·x H2O 1 (x ≈250) containing nanosized ring-shaped clusters which capture the oxidation product of cysteine, i.e. the diprotonated cystine ligands (H2cystine+) at the inner wall of their cavities; interestingly, the multiphilic ligands containing different types of functional groups (two –NH3+, one –CO2−, one –CO2H and one –S–S–) attach to the inner wall of the cluster through one of the two carboxylate groups thereby demonstrating the possibility to generate novel type surfaces within the cavity of a nanostructured ring-shaped cluster.

A hydrogen-bonded cluster with ‘onion-type’ structure, encapsulated and induced by a spherical cluster shell: [(H2O)n⊂ MoVI72MoV60O372(HCO2)30(H2O)72]42–

By reacting an aqueous solution of ammonium heptamolybdate with formic acid in the presence of hydrazinium sulfate at pH ≈ 4.2 the compound (NH4)42[MoVI72MoV60-O372(HCO2)30(H2O)72]·xHCO2Na·yH2O 1 (x ≈ 30, y ≈ 250) with spherically shaped stable cluster anions is obtained; owing to the spherical shape of the cluster–shell template, the anion 1a (with the small ‘nondisturbing’ bidentate HCO2– ligand) exhibits a remarkable overall ‘onion-type’ structure, thereby revealing also a novel type of inclusion: a hydrogen-bonded cluster with ‘onion-type’ structure, which suggests interesting aspects for a new type of supramolecular chemistry.

‘Adding’ stable functional complementary, nucleophilic and electrophilic clusters: a synthetic route to [{(SiW11O39)Mo3S4(H2O)3(µ-OH)}2]10– and [{(P2W17O61)Mo3S4(H2O)3(µ-OH)}2]14– as examples

Stable functional complementary clusters, i.e. of the electrophilic and nucleophilic type, can be ‘added’ resulting in the planned formation of the related reaction products: the high-yield synthesis of the crystalline compounds [Me2NH2]10- [{(SiW11O39)Mo3S4(H2O)3(µ-OH)}2]·20H2O 1 and [Me2NH2]14[{(P2W17O61)Mo3S4(H2O)3(µ-OH)}2]·25H2O 2 containing the related {Mo3S4}4+ as well as {W11O39}8– and {W17O61}10– clusters as constituents, respectively, is a good example.

Bemerkenswerte Wirt-Gast-Beziehungen in Tetraphenylphosphoniumsalzen vontris-Trithiocarbonato-Komplexen des As(III), Bi(III) und Fe(III)

SummaryThe structure and packing of the lattice of the compounds (PPh4)3[As(CS3)3] (1), (PPh4)3[Bi(CS3)3] (2), and (PPh4)3[Fe(CS3)3]·H2O (3) is discussed in terms of hostguest chemistry in a “soft” matrix of large cations. The hitherto unknown Fe-complex was characterized by elemental analysis and single crystal structure analysis. Here CS32− acts as a classical bidentate ligand, whereas in the case of the arsenic and bismut complexes, the coordination of this ligand is essentially unidentate due to an interaction with the lone pair on the central atom. For the last two complexes, there seems to be an influence of the packing on the coordination geometry.