Oligomers and Polymers based on Metal Ion-Pyridine Ligation

Oligomers and Polymers based on Metal Ion-Pyridine Ligation 

The first examples of porphyrin coordination polymers that have been characterized according to our definition in Sect. 3.1 were reported in 1991 by Fleischer and Shachter [72]. Upon metalation of 5-pyridyl-10,15,20-triphenyl-porphyrin with a Zn ion, a self-complementary building block was obtained which readily assembles to polymer 19 as confirmed by concentration dependent UV/vis spectroscopy and NMR studies. The structure of the polymer 19 in the solid state was established by X-ray analysis. Recent reinvestigations of this system suggest that in solution tetrameric squares prevail, and polymer formation may take place at higher concentration ( 1 M) as predicted by computer simulation [12]. 

A structurally related system was reported by Burrell et al. with the difference that the pyridine ligand is attached to one of the pyrrole rings and bridged by an ethene group which offers ds/irons isomers [73]. While the ds isomer forms a defined dimer, the irons isomer self-assembles to a coordination polymer. Both structures were confirmed by single crystal X-ray analysis. UV irradiation (400 nm) of the coordination polymer in the irons 

Two more examples of coordination polymers have recently been introduced by this group applying Co + and Ga metal ions in a porphyrin framework analogous to the dimer 11. hi both examples the porphyrin units are strongly aggregated which makes these systems potentially interesting for electronic and optoelectronic applications [ 13,76]. 

Twyman and King [77] constructed a (AA - BB) -type coordination polymer from a rigid bis(zinc porphyrin) imit 22 and a flexible ditopic pyridine 

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