TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preparation: No general preparation given. Preferred Compound: The binuclear metal complex pigment has a structure in which the lowest unoccupied molecular orbital is mainly distributed over (L1)(L1')M1. Preferred Definitions:    L1,L1'=ligand which can carry out bidentate, tridentate or tetradentate coordination, optionally substituted by -COOH or -COO-, preferably 2,2'-bipyridine-4,4'-dicarboxylic acid or 2,2'-biquinoline-4,4'-dicarboxylic acid;    ,L2,L2'=ligand which can carry out bidentate, tridentate or tetradentate coordination, preferably of formula (II), more preferably bipyridine, 1,10-phenanthroline or 2,2'-biquinoline;    BL=dihydroxy antharaquinone;and    M1,M2=ruthenium, osmium, cobalt, nickel, copper or iron.    L1,L1',L2,L2' have cyclic structure.    R11-R18=H, alkoxy, hydroxyl, optionally substituted hydrocarbon group, optionally substituted aromatic hydrocarbon ring or aliphatic hydrocarbon ring.    EXAMPLE - Ruthenium chloride (in g) (2.53), 2,2'-bipyridine-4,4'-dicarboxylic acid (4.5) and N,N-dimethyl formamide (300 ml) were refluxed for 45 minutes under 2.45 GHz microwave irradiation. The reaction mixture was filtered after cooling and the obtained filtrate was dried. The residue was washed with acetone/diethyl ether and 2 mol/l hydrochloric acid (300 ml) was added, and bis(2,2'-bipyridine-4,4'-dicarboxylic acid) ruthenium dichloride (5.75) was obtained with yield of 85%. The obtained complex (68.4 mg) was dissolved in mixture of dimethyl acetamide/water, and 1 mol/l sodium hydroxide aqueous solution (0.9 ml) was added. Ruthenium complex containing quinizarine (87.7 mg) was added to the obtained solution and refluxed for 30 minutes under 2.45 GHz microwave irradiation. Natural filtration was carried out, the filtrate was dried and the precipitate was dissolved in distilled water (30 ml). 0.5 mol/l of hexafluoro phosphate aqueous solution was added and binuclear ruthenium complex (0.084) of formula (D-1) was precipitated.