. "For example, the porphyrin complex can be produced by mixing a salt of the second transition metal (e.g., inorganic salts such as sulfate, nitrate, chloride, phosphate, and organic acid salt such as acetate, oxalate, etc.), and the porphyrin ring-containing compound, in a known solvent such as water, alcohol, aliphatic hydrocarbon, aromatic hydrocarbon, halogenated hydrocarbon, and nitriles." . . .