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

Abstract

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].