Assembling and dissembling zinc-containing coordination polymers of 4′-phenyl-4,2′:6′,4″-terpyridine

The ligand 4′-phenyl-4,2′:6′,4″-terpyridine (3) reacts with Zn(OAc)2·2H2O to yield the one-dimensional coordination polymer [Zn2(3)(OAc)4]n or [Zn(3)(OAc)2]n depending upon the reaction conditions. Both compounds have been structurally characterized. The former contains {Zn2(µ-OAc)4} units, pairs of which are connected by a bridging ligand 3, while the latter contains tetrahedral zinc(II) centres, each bonded to two terminal [OAc]− ligands and two ligands 3. Both [Zn2(3)(OAc)4]n and [Zn(3)(OAc)2]n exhibit emissive behaviour in the solid state, the emissions being significantly enhanced with respect to non-coordinated ligand 3. Protonation of the coordination polymers produces a red shift in the emission maximum. However, treatment of [Zn2(3)(OAc)4]n with MeI or EtI quenches the emission. This is a consequence of the coordination polymer being dismantled, Zn-N bonds are cleaved and the complexes [Me2(3)][ZnI4] and [Et2(3)][ZnI4] are formed. The direct reaction of 3 with an excess of MeI produces [Me2(3)]I2 with N-methylation occurring at the two outer pyridine rings as observed in [Me2(3)][ZnI4].