A Comparison of the H₂ Sorption Capacities of Isostructural Metal–Organic Frameworks With and Without Accessible Metal Sites: [{Zn₂(abtc)(dmf)₂}₃] and [{Cu₂(abtc)(dmf)₂}₃] versus [{Cu₂(abtc)}₃]

The isostructural metal–organic frameworks [{Zn2(abtc)(dmf)2}3] (1 a), [{Cu2(abtc)(dmf)2}3] (2 a), and [{Cu2(abtc)}3] (2 b; H4abtc=1,1′-azobenzene-3,3′,5,5′-tetracarboxylic acid) have high sorption capacities for H2, N2, CO2, and CH4. Solid 2 b, which has accessible metal sites (AMSs), has a higher H2 adsorption capacity than 1 a or 2 a (see picture; T=77 K), neither of which have AMSs, because of its lower molecular weight and greater isosteric heat of H2 adsorption.