Supramolecular intercluster compounds

Supramolecular chemistry aims to organize molecular building blocks by means of non- covalent interactions into complex arrangements. Efforts to synthesize suitable building blocks, to develop methods for their assembly and understand the underlying fundamental principles are currently driven over all length scales – ranging from molecules to nano-, meso- and macroscopic compounds. In particular nanoscopic self- assembly is envisioned to be the alternative to lithographic techniques for future electronic or optic devices. However, realization of such assemblies with “perfect” translational order is experimentally difficult due the intrinsic polydispersity of nanoparticles. Regarding structural and physical characterization as well as the generation of more complex assemblies, uniform, well defined nanoparticles would of course be desirable.
Our approach to overcoming the limitations of polydisperse building-blocks is to use different, well-defined, inorganic clusters of diameters being 1 nm or larger as the building-blocks for nanoscopic assemblies. By establishing methods for their crystallization we are able to study such assemblies with atomic precision, giving insight into intermolecular forces and the principles of nanoscopic assembly. The structures of such compounds are determined by the interplay of several, strong and week intermolecular interactions, e.g. ionic, dipolar, van-der-Waals, π-π interaction or hydrogen bonding. We found that especially the very week, short-range interactions are structure-directing, and thus these compounds can be referred to as supramolecular intercluster compounds (SICCs).

Examples of SICCs build from cationic gold cluster and anionic polyoxometalates.

Meanwhile, the field of intercluster compounds involves four classes

• gold phosphine clusters with polyoxometalates^[1-2]
• gold phosphine clusters with fullerides^[3]
• silver alkynyl clusters with polyoxometalates^[5-6]
• silver bipyridine clusters with polyoxometalates^[7]

Recent results:

Intercluster sandwich compound^[6]

Combination of polymeric silver compounds and the Keggin anion α-(nBu4N)5[HCoW12O40] results in formation of the first sandwich intercluster compound. The macromolecule consists of a large silver cluster, sandwiched by two Keggin anions with ligand-free interfaces between the polyanion and the silver cage.

Chain-like intercluster compounds

Combining polymeric silver alkynyl compounds with the Wells-Dawson anion α-K6[P2W18O62] has yielded chain-like intercluster compounds. The intercluster chains consist of nanometer-sized silver clusters and polyoxometalates in an alternating, linear sequence. The silver clusters are built in situ and have a previously unknown structure. The building blocks are again connected via direct bonds.

• [1] M. Schulz-Dobrick, M. Jansen: Structure-Directing Effects in the Supramolecular Intercluster Compound [Au₉(PPh₃)₈]₂[V₁₀O₂₈H₃]₂: Long-Range versus Short-Range Bonding Interactions
  Inorg. Chem. 46 (2007) 4380-4382.
• [2] M. Schulz-Dobrick, M. Jansen: Characterization of Gold Clusters by Crystallization with Polyoxometalates: the Intercluster Compounds [Au₉(dpph)₄][Mo₈O₂₆], [Au₉(dpph)₄][PW₁₂O₄₀] and [Au₁₁(PPh₃)₈Cl₂]₂[W₆O₁₉]
  Z. Anorg. Allg. Chem. 633 (2007) 2326-2331.
• [3] M. Schulz-Dobrick, M. Jansen: Intercluster Compounds Consisting of Gold Clusters and Fullerides: [Au₇(PPh₃)₇]C₆₀•THF and [Au₈(PPh₃)₈](C₆₀)₂
  Angew. Chem. Int. Ed. 47 (2008) 2256 –2259
  Angew. Chem. 120 (2008) 2288–2291.
• [4] M. Schulz-Dobrick, M. Jansen: Intermolecular forces in intercluster compounds consisting of gold clusters and fullerides and in a series of model compounds C₆₀•2(PR₃)AuCl
  Cryst. Eng. Comm. 10 (2008) 661–664.
• [5] F. Gruber, M. Schulz-Dobrick, M. Jansen: Structure-Directing Forces in Intercluster Compounds of Cationic [Ag₁₄(C≡CtBu)₁₂Cl]⁺ Building Blocks and Polyoxometalates: Long-Range versus Short-Range Bonding Interactions
  Chem. Eur. J. 16 (2010) 1464 – 1469.
• [6] F. Gruber, M. Jansen: {[Ag₄₂(CO₃)(C≡CtBu)₂₇(CH₃CN)₂][CoW₁₂O₄₀]₂}[BF₄]: An Intercluster Sandwich Compound
  Angew. Chem. Int. Ed. 49 (2010) 4924 –4926
  Angew. Chem. 122 (2010) 5044 –5046.
• [7] F. Gruber, M. Jansen: Packing requirements and short-range interactions as structure-directing forces in the intercluster compounds based on silver clusters
  Inorg. Chim. Acta (2010), doi:10.1016/j.ica.2010.06.037
• [8] F. Gruber, M. Jansen: Salt­like Structures of Oligomeric Gold Complexes and Polyoxometalates
  Z. Anorg. Allg. Chem. (2010), doi:10.1002/zaac.201000237

For more information please contact Hanne Nuss.

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