The overlooked ZIF: reviving [Cu(imidazolato)2] from 1960s literature.

Metal-organic frameworks (MOFs), and in particular zeolitic imidazolate frameworks (ZIFs), are amongst the most well studied materials in modern chemistry. MOFs emerged as an explicit subfield of chemistry in the late 1980s and 1990s. However, much foundational work was accomplished in earlier decades. Here, we detail the structural and gas-adsorption characterization of [Cu(im)2] (im = imidazolate), a ZIF that was widely reported in the early 1960s. This compound exists as several polymorphs. We re-prepared the historic blue polymorph [Cu(im)2]-B, which has a sodalite topology, confirmed its identity by single-crystal X-ray diffraction, and measured its gas-adsorption isotherms. We conclude that the true origin of ZIFs lies with a copper(II) framework discovered more than 60 years ago that has been overlooked by recent literature.