Porous purple glass – a cobalt imidazolate glass with accessible porosity from a meltable cobalt imidazolate framework

Abstract

We report the first microporous cobalt imidazolate glass obtained from a meltable cobalt-based zeolitic imidazolate framework, ZIF-62(Co). Crystalline ZIF-62(Co) is constructed from Co²⁺ cations and two different imidazolate-type linkers, namely conventional imidazolate and benzimidazolate. The microporous framework melts at ∼430 °C and converts into a glass upon cooling to room temperature. X-Ray total scattering and Raman spectroscopy reveal that the local structure of the glass and the crystalline parent material are very similar. Magnetic measurements and X-ray diffraction uncover that ZIF-62(Co) partially decomposes upon melting and glass formation resulting in the reduction of ∼3% of the Co²⁺ ions to metallic cobalt. Most importantly, the ZIF glass retains almost 50% of the porosity of crystalline ZIF-62(Co). Our results pave the way for the realisation of metal–organic framework glasses containing open shell metal ions, as well as the application of these porous glasses in gas separation, energy storage and catalysis.