Cubes on a string: a series of linear coordination polymers with cubane-like nodes and dicarboxylate linkers

Abstract

A series of semicrystalline and amorphous one-dimensional (1D) polymeric chains consisting of cubane-like Co^II₄L₄ units (L = S-1,2-bis(benzimidazol-2-yl)ethanol) and dicarboxylates were synthesized and characterized by single crystal diffraction and X-ray total scattering. The polycationic chains are composed of [Co₄L₄(dicarboxylate)]²⁺ monomeric units, while one molecular dicarboxylate counterion is balancing the charge of each monomer. The linear compound series has five members, and the crystal structures were solved for [Co₄L₄(tph)](tph) and [Co₄L₄(ndc)](ndc), where tph = terephthalate and ndc = 2,6-naphthalenedicarboxylate. Partly crystalline compounds were produced by slow assembly at elevated temperature (over days), while the amorphous compounds were formed by fast precipitation (within minutes). Pair distribution function (PDF) analysis based on X-ray total scattering data reveals the presence of the cubane-like entity in both the amorphous and semicrystalline samples. While the powders are non-porous, precipitation is a fast and versatile method to produce compounds with cubane-like centres with moderate surface areas of 17–49 m² g⁻¹ allowing for surface chemical reactions. The powders have a high concentration of Lewis base sites as verified by their selective adsorption of CO₂ over N₂. The use of an amorphous cubane-like polymer for the electrocatalytic oxygen evolution reaction was demonstrated.