NOVELTY - A metal complex comprises a polyhydric carboxylic acid compound, metal ion(s) chosen from metal ion of 2-13 group, an organic ligand which can be coordinated at multiple positions with respect to the metal ion, and a monodentate organic ligand which can be coordinated to the metal ion.    USE - Metal complex is used for adsorbents and occlusion materials (used in gas-storage apparatus e.g. fuel tank of gas motor vehicles) used for adsorbing/occluding carbon dioxide, hydrogen, carbon monoxide, oxygen, nitrogen, 1-4C hydrocarbon, noble gas, hydrogen sulfide, ammonia, sulfur oxide, nitrogen oxide, siloxane, or organic vapors, and for separation materials used for separating methane and carbon dioxide, hydrogen and carbon dioxide, nitrogen and carbon dioxide, ethylene and carbon dioxide, methane and ethane, ethane and ethylene, propane and propene, or air and methane (all claimed).    ADVANTAGE - The metal complex has excellent water resistance, adsorption, and occlusion and separation capability with respect to gas, is capable of being stably present and retaining a high adsorption ability under high temperature/humidity conditions.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) gas-storage apparatus (1) provided with a gas occlusion space (3) in the inward side of an airtight pressure-resistant container (2) equipped with an inlet entrance and exit of gas. An occlusion material (4) comprising the metal complex is provided in the gas occlusion space;    (2) gas motor vehicle provided with an internal combustion engine which generates a driving force with fuel gas supplied from the gas-storage apparatus;    (3) separation of mixed gas, which involves contacting the mixed with the metal complex at 0.01-10 MPa; and    (4) manufacture of metal complex, which involves reacting polyhydric carboxylic acid compound, metal ion(s), organic ligand, and monodentate organic ligand in a solvent.    DESCRIPTION OF DRAWING(S) - The drawing shows a conceptual view of the gas motor vehicle provided with the gas-storage apparatus.    Gas-storage apparatus (1)    Pressure-resistant container (2)    Gas occlusion space (3)    Occlusion material (4)