Disclosed is a metal complex having a partial structure represented by the following Formula (I-0) or a tautomer thereof: formula (I-0) Cy is a 5 to 7 membered heterocyclic ring, preferably a 6-membered ring, which may be aromatic, non aromatic or partially aromatic and which coordinates to the metal atom through a carbon atom; A is a nitrogen atom a is an integer equal or superior to 1; D is an electron donor group; and b is an integer equal or superior to 1.