The spatial dependence of intervalence charge transfer in an electroactive metal–organic framework

Abstract

Metal–Organic frameworks (MOFs) provide an ideal platform to examine intervalence charge transfer (IVCT) in 3-dimensional coordination space. In the family of TTF-containing MOFs based on the parent system [Cd(bpdc)₂(Py₂TTF)₂] (1), where H₂bpdc = 4,4′-biphenyldicarboxylic acid and Py₂TTF = (E)-4,4′-di(pyridin-4-yl)-2,2′-bi(1,3-dithiolylidene), substitution of the dicarboxylic acid coligand provides systematic variations in the cofacial arrangement of the IVCT-active mixed-valence TTF-ligand pairs. The resulting effects on the IVCT and radical behaviour of these frameworks was then quantified, revealing that the electronic coupling parameter, H_ab, and radical characteristics were dependent on both the cofacial distance and horizontal offset between the cofacial ligands. Elucidating these structure–function relationships provides a basis for fine-tuning MOFs towards the development of conductive porous materials for subsequent use in energy technologies such as batteries and electrocatalysts.