high density of open Ni II sites is critical for enhancing the weighted average of adsorption enthalpies in Ni2(m-dobdc) (despite a reported isosteric enthalpy of adsorption that is slightly lower than optimal: -12.3 kJ/mol), while also contributing a higher volumetric usable capacity than is observed in the MFU-4l frameworks presented here. For improving the total usable H2 storage capacity, a higher density of the adsorption sites with a binding enthalpy in the optimal range of -15 to -25 kJ/mol is clearly a requirement.