A Mn(II)-based homometallic porous metal organic framework, Mn-5(btac)(4)(mu(3)-OH)(2)(EtOH)(2)center dot DMF center dot 3EtOH center dot 3H(2)O (I, btac = benzotriazole-5-carboxylate), has been solvothermally synthesized and structurally characterized by elemental analysis, thermogravimetric analysis, and X-ray crystallographic study. I 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 H-2 adsorption measurement at 77 K reveals that activated I can absorb 0.99 wt % H-2 at 0.5 atm and reaches a maximum of 1.03 wt % at 5.5 atm. The steep H-2 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 I 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 sorption implies that the exposed Mn(II) coordination sites in the activated I play an important role to improve its adsorption capacities.