Patent ID: 8741030

Claim:
A metal complex, comprising: (I) a dicarboxylic acid compound of Formula (I): wherein R 1 , R 2 , R 3 , and R 4 are the same or different, and are each independently a hydrogen atom, an alkyl group optionally comprising a substituent, an alkoxy group, a formyl group, an acyloxy group, an alkoxycarbonyl group, a nitro group, a cyano group, an amino group, a monoalkyl amino group, a dialkyl amino group, a acylamino group or a halogen atom; or R 1 and R 2 , or R 3 and R 4 together optionally form an alkylene group or an alkenylene group optionally comprising a substituent; (II) at least one metal ion selected from the group consisting of ions of a metal belonging to Group 2 and Groups 7 to 12 of the periodic table; and (III) an organic ligand comprising 2 to 7 heteroatoms, wherein the organic ligand is capable of bidentate binding to the metal ion, the organic ligand belongs to the D ∞h point group, and the organic ligand has a longitudinal length of not less than 8.0 Å and less than 16.0 Å.