NOVELTY - A metal complex comprises dicarboxylic acid compounds (a) and (b) (I), metal ion chosen from ion of metals belonging to group-2 and groups-7-12 of periodic table, and organic ligand capable of bidentate coordination to the metal. The molar ratio of dicarboxylic acid compound (a) and dicarboxylic acid compound (b) is 20:80-99:1.    USE - Metal complex is used for adsorbent, occlusion material, and separation material for separating carbon dioxide, hydrogen, carbon monoxide, oxygen, nitrogen, 1-4C hydrocarbon, noble gas, hydrogen sulfide, ammonia, sulfur oxide, nitrogen oxide, siloxane, water vapor, organic vapor, methane, carbon dioxide and hydrogen, carbon dioxide and nitrogen, carbon dioxide, ethylene and carbon dioxide, methane and ethane, and ethane, ethylene and propane, propylene and ethylene, acetylene, nitrogen and methane, or air and methane (all claimed).    ADVANTAGE - The metal complex has excellent gas adsorption performance, gas storage performance and gas separating performance.    DETAILED DESCRIPTION - A metal complex comprises dicarboxylic acid compounds (a) and (b) of formula (I), metal ion chosen from ion of metals belonging to group-2 and groups-7-12 of periodic table, and organic ligand capable of bidentate coordination to the metal. The molar ratio of dicarboxylic acid compound (a) and dicarboxylic acid compound (b) is 20:80-99:1.    X=H or alkyl group, alkoxy, formyl, acyloxy, alkoxycarbonyl, nitro, amino, monoalkyl-amino, dialkylamino, acylamino or halo (all optionally substituted);    X of dicarboxylic acid compound (a)=electron-donating group;    X of dicarboxylic acid compound (b)=electron-attractive group;and    R1-R3=H, halo or alkyl (optionally substituted).    INDEPENDENT CLAIMS are included for the following:    (1) adsorbent;    (2) occlusion material;    (3) gas storage apparatus, which consists of pressure-resistant container provided with entrance and exit of gas, and gas-occlusion space inside the pressure-resistant container, and occlusion material;    (4) gas motor vehicle, which is provided with internal combustion engine;    (5) separation material;    (6) separation method, which involves contacting metal complex and mixed gas in pressure of 0.01-10 MPa using separation material; and    (7) manufacture of metal complex, which involves reacting organic ligand with metal salt in presence of solvent.