Sixty years ago, cupric acetate was proposed as one of the first homogeneous, heterolytic hydrogen activation catalysts. Later on, it was demonstrated that dihydrogen complexation is unequivocally the first step preceding H-H bond cleavage. In this study, using a home-made, high-pressure adsorption setup working at different temperatures, we examined the carbon-nanoconfined counterparts of the former in order to elucidate the nature of H-2-metal complex interaction inside the nanosized space provided by the porous support. In this regard, we found that by lowering temperature from 100 degrees C to room temperature, a marked alteration would take place in the nature of interaction. By doing so, we moved from what appeared to be (H-2)CuH2, a dihydride-dihydrogen complex, to a Kubas compound releasing H-2 in a fully reversible manner. The nanoconfined metal complex discussed here may serve either as a prototypical, room-temperature hydrogen storage medium with optimum heat of interaction, or as a solid-phase hydrogen activation catalyst operating under mild conditions. (C) 2016 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.