Structure and Synthesizability of Iron-Sulfur Metal-Organic Frameworks

Sulfur-based metal-organic frameworks (MOFs) and coordination polymers (CPs) are an emerging class of hybrid materials that have received growing attention due to their potential magnetic, conductive, and catalytic properties with applications in electrocatalysis and energy storage. In this work, we report a high-throughput virtual screening protocol to predict the synthesizability of candidate metal-sulfur MOFs/CPs by computing the thermodynamically stable structures resulting from a particular combination of metal cluster, linker, cation, and synthetic conditions. Free energies are computed using all-atom classical mechanical thermodynamic integration. Low-free energy structures are refined using ab initio density functional theory, and pair distribution functions and powder X-ray diffraction patterns calculated to complement and guide experimental structure determination. We validate the computational approach by retrospective predictions of the stable structure produced by experimental syntheses, and a subsequent screen predicts Fe4S4-BDT--TPP as a new thermodynamically stable 1D CP comprising a redox-active Fe4S4 cluster, 1,4-benzenedithiolate (BDT) linker, and tetraphenylphosphonium (TPP) countercation. This material is experimentally synthesized and the 1D chain structure of the crystal confirmed using microcrystal electron diffraction. The computational screening pipeline is generically transferable to neutral and ionic MOFs/CPs comprising arbitrary metal clusters, linkers, cations, and synthetic conditions, and we make it freely available as an open source tool to guide and accelerate the discovery and engineering of novel porous materials.