Anion-directed assembly of helical copper(ii) complexes based on a bispyridylpyrrole ligand: synthesis, structural and magnetic properties

Abstract

Helical copper(II) complexes based on a bispyridylpyrrole ligand, namely the helical polymer {[Cu₂(PDP_H)₂(N₃)₂]}_n (1) (where HPDP_H = 2,5-bis(2′-pyridyl)pyrrolide) containing a one-dimensional double-helical chain, a discrete double-helical complex [Cu₂(PDP_H)₂(NO₃)₂] (2) and triple-helical complex [Cu₂(PDP_H)₃](OTf) (3·OTf) (where OTf⁻ = triflato) were synthesized by displacement of Cl⁻ in [Cu(PDP_H)Cl] by the anion N₃⁻, NO₃⁻ and OTf⁻, respectively. The structures of these complexes directly correlate with the coordination abilities of the ligands. The N₃⁻ anion is found to favor the formation of polymeric helical structures. The helical chain in 1 is built-up by [Cu₂(PDP_H)₂] units linked by double μ_1,3-azido bridges. In 2, the anion NO₃⁻ acting as a monodentate oxygen ligand binds to each copper center, resulting in the formation of the double helical structure, while the non-coordinating OTf⁻ ligand leaves space for three PDP_H⁻ ligands, leading to the formation of the triple-helical dicopper complex 3·OTf. Magnetic susceptibility data of 1, measured from 1.8 to 300 K, show alternating ferro- and antiferromagnetic interactions through the bridging PDP_H⁻ and μ_1,3-azido pathway, respectively.