Incorporation of low-valent metal ions in metal-organic frameworks and coordination polymers

Despite the prevalence of low-valent metal complexes and their critical role in processes such as catalysis, luminescence, etc., the use of low-valent metals as structural components of metal-organic frameworks (MOFs) is surprisingly rare. Typical MOFs rely on the interaction of hard, Lewis basic multitopic ligands (such as carboxylates) with hard Lewis acidic high-valent metal ions for framework construction. By contrast, low-valent metal-organic frameworks (LVMOFs) are constructed from soft Lewis basic ligands with metals in their (0) or (+1) oxidation states. The relatively rare instances of LVMOFs have been investigated for a variety of applications, particularly as heterogeneous catalysts for small molecule transformations. Beyond LVMOFs, strategies such as postsynthetic modification (PSM) have also been used to incorporate low-valent metals into canonical MOFs. In this review, the development of LVMOFs and related materials, namely low-valent, one-dimensional coordination polymers (CPs) are presented. In addition, MOFs with low-valent metals incorporated via PSM are also discussed. • An overview of reported low-valent MOFs (LVMOFs) and related materials is presented. • A survey of metals and ligands used for constructing LVMOFs is described. • Low-valent CPs and MOFs with low-valent metals appended through PSM are also discussed.