Self-assembled Transition Metal Coordination Frameworks of ...

Chapter I _ g
plays a pivotal role in the formation of metallosupramolecular squares in high yields
by avoiding other macrocyclic or polymeric by-products [13].
Taking together all the information available on metal-directed self-assembly,
it can be concluded that the formation of metallosupramolecular squares is a more
complex process than simple chemical equations of their preparation disclose [13].
For a typical self-assembly process, open polymeric intermediates have to be
considered which can be transformed to a specific macrocyclic product only under the
conditions of reversibility. The possible equilibria in such a self-assembly process are
schematically presented [13] in Fig. 1.1. As can be seen, the coordinative interactions
between metals and ligands lead initially to the formation of openchain oligomers (n =
1, 2, 3,. . .00), which may be transformed to the corresponding cyclic products through
a macrocyclization process. In this context, the generation of a specific macrocycle
depends on its thermodynamic advantage compared to other cyclic species. In order to
achieve this desired situation, the building blocks must be designed properly.
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Fig. l.l. Possible equilibria between linear and cyclic oligomeric species in the selfassembly
process (metal comers shown as circles, ditopic ligands shown as
connecting the corners).
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