Discrete and polymeric supramolecular complexes assembled from Cu2+ and isomeric xylylenebis(pyridyltriazoles)

Abstract

The coordination chemistry of Cu²⁺ with three isomeric xylylene-bridged bis-chelating pyridyltriazole ligands (o-xpt, m-xpt, and p-xpt) is systematically explored. These ligands were chosen for their ability to form trans-planar chelating coordination modes, in contrast to the commonly studied 2,2′-bipyridine analogs. The o-xpt and m-xpt ligands consistently form box-like binuclear complexes of the type [Cu₂(xpt)₂]⁴⁺, with square-pyramidal coordination geometries around the metal centers. For o-xpt, the Cu⋯Cu distance is approximately 4.1 Å, with intramolecular contacts of 3.4–3.8 Å between pyridyltriazole moieties that indicate π–π interactions. The m-xpt ligand forms more flexible [Cu₂(m-xpt)₂]⁴⁺ complexes with Cu⋯Cu distances ranging from 6.8 to 8.8 Å. In contrast, the p-xpt ligand produces a variety of structures, including 1-D coordination polymers, a triple-stranded helicate, or a polymeric network of macrocyclic dimers linked by additional p-xpt ligands, depending on the experimental conditions. Notably, 1,4-diazabicyclo[2.2.2]octane (dabco) functions as a templating agent to direct the assembly of a discrete binuclear complex, [Cu₂(p-xpt)₂(μ-dabco)]⁴⁺; [Cu₂(p-xpt)₂]⁴⁺ species could not be obtained in the absence of the template. Single-crystal X-ray analyses of representative complexes from all three ligand isomers reveal the structural diversity and influence of ligand topology on coordination geometries and supramolecular assemblies.