A magnesium borohydride framework with small pores and a partially negatively charged inner surface enables dense hydrogen storage. Using neutron powder diffraction, volumetric gas adsorption, inelastic neutron scattering, and first-principles calculations, researchers investigated the framework's ability to adsorb hydrogen and nitrogen. Hydrogen and nitrogen occupy distinct adsorption sites, with hydrogen having a much higher limiting capacity (2.33 H₂ per Mg(BH₄)₂) compared to nitrogen (0.66 N₂ per Mg(BH₄)₂). Hydrogen is packed densely, achieving a density twice that of liquid hydrogen (144 g H₂ per litre of pore volume). A penta-dihydrogen cluster was identified, where hydrogen molecules have different orientations and interactions with the framework. This study shows that dense hydrogen can be stabilized in small-pore materials at ambient pressures. The framework's unique structure allows for high volumetric and gravimetric hydrogen storage, with hydrogen density reaching 8.0 mass fraction (wt%) at saturation. The framework also supports two distinct hydrogen adsorption sites, D11 and D22, with D11 hosting fully rotated hydrogen molecules and D22 hosting molecules with directional interactions. The framework's ability to store hydrogen at high densities is attributed to short contact distances between hydrogen atoms and the framework, as well as the formation of penta-dihydrogen clusters. The study highlights the potential of this framework for high-density hydrogen storage and future applications in superconductivity and stability.A magnesium borohydride framework with small pores and a partially negatively charged inner surface enables dense hydrogen storage. Using neutron powder diffraction, volumetric gas adsorption, inelastic neutron scattering, and first-principles calculations, researchers investigated the framework's ability to adsorb hydrogen and nitrogen. Hydrogen and nitrogen occupy distinct adsorption sites, with hydrogen having a much higher limiting capacity (2.33 H₂ per Mg(BH₄)₂) compared to nitrogen (0.66 N₂ per Mg(BH₄)₂). Hydrogen is packed densely, achieving a density twice that of liquid hydrogen (144 g H₂ per litre of pore volume). A penta-dihydrogen cluster was identified, where hydrogen molecules have different orientations and interactions with the framework. This study shows that dense hydrogen can be stabilized in small-pore materials at ambient pressures. The framework's unique structure allows for high volumetric and gravimetric hydrogen storage, with hydrogen density reaching 8.0 mass fraction (wt%) at saturation. The framework also supports two distinct hydrogen adsorption sites, D11 and D22, with D11 hosting fully rotated hydrogen molecules and D22 hosting molecules with directional interactions. The framework's ability to store hydrogen at high densities is attributed to short contact distances between hydrogen atoms and the framework, as well as the formation of penta-dihydrogen clusters. The study highlights the potential of this framework for high-density hydrogen storage and future applications in superconductivity and stability.