NOVELTY - A gas separation material selectively separates target gas containing 2C or 4C hydrocarbon gas having carbon-carbon double bond from mixed gas containing target gas and hydrocarbon gas having same carbon number as target gas. The gas separation material contains a metal complex comprising 2,3-pyrazine dicarboxylic acid, ion of metal (M) chosen from beryllium, magnesium, calcium, strontium, barium, titanium, vanadium, chromium, manganese, iron, ruthenium, cobalt, rhodium, nickel, palladium, platinum, copper, zinc and cadmium, and organic ligand (I) or (II).    USE - Gas separation material for adsorbing sheet and separation membrane used for separating hydrocarbon gas e.g. ethylene and 1,3-butadiene (all claimed).    ADVANTAGE - The gas separation material efficiently enables separation and recovery of target gas from mixed gas.    DETAILED DESCRIPTION - A gas separation material selectively separates target gas containing 2C or 4C hydrocarbon gas having carbon-carbon double bond from mixed gas containing target gas and hydrocarbon gas having same carbon number as target gas. The gas separation material contains a metal complex comprising 2,3-pyrazine dicarboxylic acid, ion of metal (M) chosen from beryllium, magnesium, calcium, strontium, barium, titanium, vanadium, chromium, manganese, iron, ruthenium, cobalt, rhodium, nickel, palladium, platinum, copper, zinc and cadmium, and organic ligand of formula (I) or (II) and capable of bidentate coordination to metal ion. The metal complex has compositional formula: (M2+)2(A2-)2B'.    X=-CH2-, -CH2-CH2-, -CH2-CH2-CH2-, -CH=CH-, -CC-, -O-, -S-, -S-S-, -N=N- or -NHCO-;    R1-R12=H, optionally substituted 1-4C alkyl, 2-4C alkenyl, 1-4C alkoxy, formyl, 2-10C acyloxy, 2-4C alkoxycarbonyl, nitro, cyano, amino, 1-4C monoalkyl amino, 2-4C dialkylamino, 2-4C acylamino or halo;    M2+=ion of metal (M);    A2-=2,3-pyrazine dicarboxylic acid di-anion;and    B'=organic ligand capable of bidentate coordination with metal ion.    INDEPENDENT CLAIMS are included for the following:    (1) separation method of 2C or 4C hydrocarbon gas, which involves contacting 2C or 4C hydrocarbon gas having carbon-carbon double bond as target gas and hydrocarbon gas of the same carbon number as the target gas with gas separation material, selectively adsorbing target gas to separation material, and collecting the desorbed target gas;    (2) separation membrane containing porous support and the gas-separation material adhered to the surface layer portion of porous support; and    (3) adsorbing sheet containing the gas-separation material and the organic fiber.