Supramolecular cation, formation

Having introduced the major principles of complexation, association, and organization, it is important to review the physicochemical forces that lead to supramolecular ensemble formation. As mentioned above, supramolecular interactions are by definition noncovalent. In the order of the polarity of the partners involved, they comprise ionic or electrostatic interactions,17 18 ion-dipole interactions,19 dipole-dipole interactions, (ionic) hydrogen bonding, cation-tt and anion-tt interactions,... 

Cr CN)s] 6(CI04)3 showing the intermolecular interactions between six dinuclear Cu —Cr units (a), which lead to the formation of a cyclic dodecanuclear supramolecular complex (b), which is cocrystallized with a heptanuclear supramolecular cation that consists of a central hexacyanochromate fragment surrounded by six weakly interacting Cu(II) units (c). 

Polyoxometalates also play an important role in the selection of a metal ion for its complete encapsulation in the cavity of a crown ether to form an unusual supramolecular cation structure. For example, the crown ethers (macrocyclic polyethers), generally, do not readily form complexes with first-row transition metals in their low oxidation states because such metal ions provide only soft coordination (acceptor) sites and crown ethers have hard donor atoms. Naturally, only a few first-row transition metal rown ether complexes had been structurally characterized in which a direct bond formation between a transition metal and the crown ether oxygen atoms became possible rare examples of this kind are offered by the smaller ring crown ethers (e.g., 15-crown-5 and... 

As in the case of the gold-silver analogous systems, perhaps the most productive method for preparing extended systems through metallophilic interactions is the acid-base process, in which basic gold(I) precursors react with metallic Lewis acids forming supramolecular networks via acid-base stacking. The cation-anion interactions assist the formation of extended chains. 

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