Hydrogen Storage and Selective, Reversible O2 Adsorption in a Metal–Organic Framework with Open Chromium(II) Sites

A chromium(II)-based metal-organic framework Cr-3[(Cr4Cl)(3)(BTT)(8)](2) (Cr-BTT; BTT3 = 1,3,5-benzenetristetrazolate), featuring coordinatively unsaturated, redox-active Cr2+ cation sites, was synthesized and investigated for potential applications in H-2 storage and O-2 production. Low-pressure H-2 adsorption and neutron powder diffraction experiments reveal moderately strong Cr-H-2 interactions, in line with results from previously reported M-BTT frameworks. Notably, gas adsorption measurements also reveal excellent (2)/N-2 selectivity with substantial O-2 reversibility at room temperature, based on selective electron transfer to form Cr-III superoxide moieties. Infrared spectroscopy and powder neutron diffraction experiments were used to confirm this mechanism of selective O-2 binding.