Cluster-arene interactions

Hg3 can be synthesized in GaCl3-benzene solution either by a symproportionation of Hg2 " and mercury metal or by direct oxidation of mercury metal by GaCL. The latter route has interesting implications, since mercury metal is only very sparingly soluble in neat, molten GaCb. It therefore seems plausible that interactions with benzene stabilizes Hgj in such solutions and therefore renders mercury metal more susceptible to oxidation. Cluster-arene interactions are discussed in more detail in Sec. 1.29.4.6. 

Electrostatic interactions play a dominant role in weak molecular clusters between components, like arenes, exhibiting quadrupole momenta q. The global minimum of the benzene dimer corresponds to structure with monomers located in perpendicular planes (T-shape structure). " This structure is favored by attractive... 

Hie coordination chemistry of quinoline (Q) does not differ significantly from that of Py except for the interactions with metal clusters. In this case, the presence of the carbocyclic ring allows a larger variety of bonding modes, summarized in Fig. 6.5. As for Py, the most common coordination mode of Q in mononuclear complexes is the t (N) [45, 47-51], and it is often in equilibrium with the T -arene form. 

Braga and Grepioni have undertaken a series of analyses of the crystal structures of metal carbonyl clusters, 7t-arene complexes, mixed carbonyl n-arene complexes and some substituted derivatives [170]. Their analyses are based on examination of the packing details and motifs in the crystal structures, recognition of specific interactions, calculation of the packing potential energy for the crystal and consideration of contributions to the lattice volume. Their objective, to investigate the interplay between molecular structure and crystal structure, is very similar to the perspective in this article. 

They include, for example, arenes and cyclopentadienyl ligands and, especially in binuclear or cluster complexes, methylene (//-CH2) and methylidcne (/ij-CH) groups. Figure 5.5 depicts the p-CR2- OC and p CH- -OC bonding interactions in methylene and methylidene metal clusters. 

In contrast to these promising results with resorcin[4]arene-based clusters, glucosyl-functionalised calix[6]arene 11 and calix[8]arene 12 (Fig. 22.3) are unable to condense DNA, despite being able to interact with phosphate anions [25]. AFM studies of their interaction with plasmid DNA gave evidence of binding and the formation of aggregates but not of the formation of the compact particles required for transfection. 

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