Recent studies have focused on metal-organic frameworks (MOFs) with high hydrogen uptake1 in order to reach the 2010 DOE targets for on-board vehicular hydrogen storage.2 Strategies such as using pore sizes comparable to hydrogen molecules3 and introducing coordinatively unsaturated metal centers (UMCs)3b,c,4 have been explored. Recently, we have reported a biomimetic approach to UMCs utilizing entatic metal centers (EMCs).5 We have also demonstrated in both PCN-63c (porous coordination net-works) and PCN-95 that interpenetration is an important factor contributing to their respective hydrogen uptake. However, inter-penetration (or framework catenation) as an independent criterion has never been resolved from other factors. Normally in a given metal-ligand combination, either an interpenetrated network or a non-interpenetrated network is favored, not both. Conceptually, an interpenetrated MOF and its non-interpenetrated counterpart
Ma et al. (2007) studied this question.