High-Enthalpy Hydrogen Adsorption in Cation-Exchanged Variants of the Microporous Metal−Organic Framework Mn3[(Mn4Cl)3(BTT)8(CH3OH)10]2

Exchange of the guest Mn2+ ions in Mn3[(Mn4Cl)3(BTT)8(CH3OH)10]2 (1-Mn2+; BTT=1,3,5-benzenetristetrazolate) with selected cations results in the formation of isostructural framework compounds 1-M (M=Li+, Cu+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+). Similar to the parent compound, the new microporous materials are stable to desolvation and exhibit a high H2 storage capacity, ranging from 2.00 to 2.29 wt % at 77 K and 900 torr. Measurements of the isosteric heat of adsorption at zero coverage reveal a difference of 2 kJ/mol between the weakest and strongest H2-binding materials, which is attributed to variations in the strength of interaction between H2 molecules and unsaturated metal centers within each framework. The Co2+-exchanged compound, 1-Co2+, exhibits an initial enthalpy of adsorption of 10.5 kJ/mol, the highest yet observed for a microporous metal-organic framework.