Metal complex and adsorbent material, storage material, and separating material comprising same

A metal complex comprising:

• two different dicarboxylic acid compounds (I-1) and (I-2) each of which is a dicarboxylic acid compound (I) of formula (I),
• wherein
• X is a hydrogen atom, an alkyl group that may have a substituent, an alkoxy group, a formyl group, an acyloxy group, an alkoxycarbonyl group, a nitro group, an amino group, a monoalkyl amino group, a dialkyl amino group, an acylamino group, or a halogen atom,
• R1, R2, and R3 are the same or different, and are each independently a hydrogen atom, an alkyl group that may have a substituent, or a halogen atom, and
• X of the dicarboxylic acid compound (I-1) is an electron-donating group, and X of the dicarboxylic acid compound (I-2) is an electron-withdrawing group;
• at least one kind of metal ion selected from metal ions belonging to Group 2 and Groups 7 to 12 of the periodic table;
• and
• an organic ligand capable of bidentate binding to the metal ion, wherein a molar ratio of the dicarboxylic acid compound (I-1) to the dicarboxylic acid compound (I-2) is from 20:80 to 99:1.