Mn(II)-Based Porous Metal–Organic Framework Showing Metamagnetic Properties and High Hydrogen Adsorption at Low Pressure

A Mn(II)-based homometallic porous metal–organic framework, Mn5(btac)4(μ3-OH)2(EtOH)2·DMF·3EtOH·3H2O (1, btac = benzotriazole-5-carboxylate), has been solvothermally synthesized and structurally characterized by elemental analysis, thermogravimetric analysis, and X-ray crystallographic study. 1 is a 3D neutral framework featuring 1D porous channels constructed by {Mn–OH–Mn}n chains and btac linkers. Magnetic studies show that 1 is a 3D metamagnet containing 1D {Mn–OH–Mn}n ferrimagnetic chains. High-pressure H2 adsorption measurement at 77 K reveals that activated 1 can absorb 0.99 wt % H2 at 0.5 atm and reaches a maximum of 1.03 wt % at 5.5 atm. The steep H2 absorption at lower pressure (98.2% of the storage capacity at 0.5 atm) is higher than the corresponding values of some MOFs (MIL-100 (16.1%), MOF-177 (57.1%), and MOF-5 (22.2%)). Furthermore, activated 1 can adsorb CO2 at room temperature and 275 K. The adsorption enthalpy is 22.0 kJ mol–1, which reveals the high binding ability for CO2. Detailed gas...