NOVELTY - A metal complex contains dicarboxylic acid compound (I), metal ion chosen from II group element and VII-XII group element and organic ligand in which bidentate coordination is enabled with respect to metal ion and having 6-12 hetero atoms. The organic ligand has point group (D) of 8-15.5 Angstrom in length along major axis direction. The organic ligand excludes 3,6-di(4-pyridyl)-1,2,4,5-tetrazine.    USE - Metal complex used for adsorbent for adsorbing carbon dioxide, hydrogen, carbon monoxide, oxygen, nitrogen, 1-4C hydrocarbon, noble gas, hydrogen sulfide, ammonia, sulfur oxide, nitrogen oxide, siloxane, water vapor or organic vapor, occlusion material for occluding carbon dioxide, hydrogen, carbon monoxide, oxygen, nitrogen, 1-4C hydrocarbon, noble gas, hydrogen sulfide, ammonia, water vapor or organic vapor, 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 or organic vapor, and separating methane and carbon dioxide, carbon dioxide and ethylene, carbon dioxide and hydrogen, nitrogen and carbon dioxide, air and methane, methane and ethane, ethane and propane, propane and propene, ethylene and ethane, and acetylene and methane (all claimed).    ADVANTAGE - The metal complex provides excellent gas adsorption characteristics, gas occlusion property and gas separation property.    DETAILED DESCRIPTION - A metal complex contains dicarboxylic acid compound of formula (I), metal ion chosen from II group element and VII-XII group element and organic ligand in which bidentate coordination is enabled with respect to metal ion and having 6-12 hetero atoms. The organic ligand has point group (D) of 8-15.5 Angstrom in length along major axis direction. The organic ligand excludes 3,6-di(4-pyridyl)-1,2,4,5-tetrazine.    R1-R8=H, halo, optionally substituted alkyl, alkoxy, formyl, acyloxy, alkoxycarbonyl, nitro, cyano, amino, monoalkyl amino, dialkylamino or acylamino;and    R2+R3 or R6+R7=alkylene or alkenylene (both optionally substituted).    An INDEPENDENT CLAIM is included for manufacture of metal complex, which involves reacting metal ion, dicarboxylic acid compound and organic ligand in a solvent, and depositing.