Hydrothermal syntheses, crystal structures and properties of novel quinone biradical and mixed-valence copper coordination polymer with semiquinone radical ligand generated in situ

Abstract

A novel quinone biradical (1) was hydrothermally synthesized through ZnCl₂ mediated decarboxylation and carbon–carbon coupling reactions using the 2-(imidazo[1,2-a]pyridin-2-yl)-2-oxoacetic acid radical. Interestingly, when CuCl₂ was used instead of ZnCl₂, a new mixed-valence copper coordination polymer (2) with semiquinone radical anion ligand was obtained. The possible formation mechanism of these two compounds is proposed. The EPR and magnetic susceptibility data suggest that 1 is a biradical. The EPR and XPS results support that 2 is a mixed-valence copper coordination polymer. The quinone biradical 1 forms a one-dimensional (1D) columnar stacking chain. The coordination polymer 2 consists of a two-dimensional (2D) layered framework constructed by 1D corrugated double-stranded stair-like inorganic [CuCl]_n chains and bridged semiquinone radical anion ligands. 1 and 2 exhibit antiferromagnetic coupling interactions and different luminescent colors.