cis- and trans-9,10-di(1H-imidazol-1-yl)-anthracene based coordination polymers of ZnII and CdII: synthesis, crystal structures and luminescence properties

Abstract

New functional coordination polymers based on the semi-flexible 9,10-di(1H-imidazol-1-yl)-anthracene ligand (L) with Zn^II and Cd^II, namely {[Zn(μ₂-L)₂](ClO₄)₂·m(MeOH)·n(DCM)}_n (1), {[Zn(μ₂-L)₂](BF₄)₂·m(MeOH)·n(DCM)}_n (2), {[Zn(μ₂-L)₂(p-Tos)₂]·m(DCM)·n(MeOH)}_n (3), {[Cd(μ₂-L)₂(p-Tos)₂]·m(DCM)}_n (4) {[Cd(μ₂-L)₂(p-Tos)₂]·m(MeOH)·n(Dioxane)}_n (5) and {[Zn(μ₂-L)₂(CF₃CO₂)₂]·2(Dioxane)}_n (6), were obtained. Dissolving L in polar solvent mixtures MeOH–DCM (4 : 1) or MeOH–dioxane (1 : 1) with Zn^II and Cd^II salts resulted in the formation of complexes 1, 2, and 5 adopting a cis-conformation of the imidazole groups with respect to anthracene. In less polar mixtures of solvents such as MeOH–DCM (1 : 4) trans-L is observed, leading to the coordination polymers 3–4 with Zn^II and Cd^II. In an intermediate solvent mixture such as MeOH–dioxane (1 : 4), the cis- and trans-conformation coexist as exemplified in complex 6 with Zn^II. In the solid state, complexes 1–5 assemble as supramolecular 2-D coordination polymers with a (4,4) topology, while 6 forms a tridimensional porous network with a cds topology. All compounds reveal strong blue emission in the solid state at room temperature.