Unveiling Novel Polymorphs of Zirconium-Based Metal–Organic Frameworks from De Novo Syntheses and Phase Transformations

Polymorphism grants metal–organic frameworks (MOFs) a high degree of structural diversity for various applications. Here, we describe the discovery of three new phases of zirconium-muconate MOFs, denoted as NU-412 (bct), NU-413 (bcu), and NU-414 (reo). NU-412 was first synthesized using formic acid as both modulator and coligand de novo and was crystallographically characterized. The formate coligand in NU-412 could be selectively removed to yield NU-413 with a higher degree of coordinative unsaturation at the Zr6 node and maintained the channel geometry of the structure. Inspired by the intermediate NU-414 product observed during the growth of NU-412, we investigated the possibility of phase transformations as an approach to yield NU-412 and demonstrated success in accessing novel polymorphs from existing phases.