NOVELTY - A metal complex consists of a metal ion chosen from group II and group(s) VII-XII and/or dicarboxylate ion (I), and an organic ligand, in which bidendate coordination is possible. The organic ligand containing two heteroatoms, has a point group of D(infinity)h, and length of 7-16 Angstrom in major axis direction.    USE - Metal complex is used for adsorbent, occlusion material and separation material for adsorbing, occluding and separating, respectively, carbon dioxide, hydrogen, carbon monoxide, oxygen, nitrogen, 1-4C hydrocarbon, noble gas, hydrogen sulfide, ammonia, sulfur oxide, nitrogen oxide, siloxane or organic vapor. Occlusion material is used in gas storage apparatus for gas motor vehicle (all claimed).    ADVANTAGE - The metal complex has excellent gas-adsorption performance, gas-occlusion capacity and gas-separation performance.    DETAILED DESCRIPTION - A metal complex consists of a metal ion chosen from group II and group(s) VII-XII and/or dicarboxylate ion of formula (I), and an organic ligand, in which bidendate coordination is possible. The organic ligand containing two heteroatoms, has a point group of D(infinity)h, and length of 7-16 Angstrom in major axis direction.    R1,R2=H, alkyl optionally having halo or substituent, alkoxy, formyl, acyloxy, alkoxycarbonyl, nitro, cyano, amino, monoalkylamino, dialkylamino or acylamino;and    A=phenylene or ethenylene.    INDEPENDENT CLAIMS are included for the following:    (1) gas storage apparatus which can be maintained in airtight state and which consists of a pressure-resistant container provided with entrance and exit of gas, and a gas occlusion space containing occlusion material provided inside the pressure-resistant container;    (2) gas motor vehicle provided with an internal combustion engine, which obtains a driving force with a fuel gas supplied from the gas storage apparatus;    (3) separation method, which involves contacting the metal complex and a mixed gas, under 0.01-10 MPa; and    (4) manufacture of metal complex, which involves reacting metal ion and organic ligand, in the presence of a solvent.