Self-assemblies through coordination complexes

An interesting dimension of metal-coordinated self-assembly that is often ignored, or at least not exploited to its fullest extent, occurs when the resulting coordination complex is a charged species and, as such, in need of a counterion. This counterion itself presents yet another subtle instance of ionic self-assembly, which often is overshadowed by its partner, the coordination complex. The second multi-functional side-chain supramolecular polymer system is based on this simple but important concept [14, 106-111]. In 2003, Ikkala and coworkers reported a study in which they exploited (1) a side-chain functionalized polymer, poly(vinyl-pyridine), (2) metal-coordination self-assembly via a tridentate Zn2+ complex and (3) ionic self-assembly through functionalized counterions, i.e. dodecylbenzene-sulfonate ions, to form multiple self-assembled complexes which adopted a cylindrical morphology (Fig. 7.23) [112]. 

The self-assembly behaviour and complexing properties of several strapped porphyrin-incorporated melamine-cyanuric or melamine-barbiturate-based rosette supramolecules in chloroform-d has produced some intriguing structures. The almost perfect H-bonding complementarity of the constituent units, amphfied by their multiphcity, results in particularly stable structures whose integrity is maintained in solution [42]. Strapped porphyrin cyanuric acid 40a and its Zn (II) complex 40b were designed to combine with melamine derivatives 41 to afford stable porphyrin rosettes 42. The new porphyrin rosettes 42 could efficiently complex tripyridyl derivative 43 through intermolecular, cooperative coordination between Zn (II) and pyridine to form the stable rosette 44. 

The structural chemistry of some metal dithiocarbamates, i.e. systematics, coordination modes, crystal packing, and supramolecular self-assembly patterns of nickel, zinc, cadmium, mercury,363 organotin,364 and tellurium,365 366 complexes has been thoroughly analyzed and discussed in detail. Supramolecular self-assembly frequently occurs in non-transition heavier soft metal dithiocarbamates. Thus, lead(II),367 bismuth(III)368 zinc,369 cadmium,370 and (organo)mercury371 dithiocarbamates are associated through M- S secondary bonds, to form either dimeric supermolecules or chain-like supramolecular arrays. The arsenic(III)372 and antimony(III)373 dithiocarbamates are... 

The protonat monomeric Pd" complex [Pd(HL )Cl]Cl (99), formed in a manner similar to that of 96, on treatment with NaOH and NaQ04 formed the self-assembled deprotonated cyclic tetramer [ Pd(L ) 4](Q04)4 (100) (97AGE1860). Thus, the metal ion also determines the nuclearity of the oligomeric species through its coordinative requirements. 

Many of the complexes prepared through subcomponent self-assembly underwent clean substitution chemistry, which may operate both at covalent and coordinative levels. As discussed below, driving forces for such substitutions included the relief of steric encumbrance, the substitution of an electron-poor subcomponent for an electron-rich one, the use of pK i differentials, and the chelate effect. 

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