An organic electroluminescent device is described which comprises a compound having a skeleton of the formula: which skeleton can comprise one or more additional aromatic rings, wherein each of Z and Z′, which may be the same or different, represents a nitrogen-containing aromatic ring such that the Z and Z′ rings either together form a conjugated system, optionally with one or more additional aromatic rings, or at least one of Z and Z′ form a conjugated system with one or more additional aromatic rings to which Z and Z′ is attached, with the proviso that, (a) when the two said rings are pyridyl rings and are connected to one another ortho to the nitrogen atoms then (i) at least one said ring is substituted by at least one electron withdrawing substituent which is a hydrocarbon aryl group or (ii) at least one said ring is fused to another aromatic ring to which the other pyridyl ring is not fused or (iii) the two said rings together form a phenanthroline ring system which is substituted by at least one electron withdrawing substituent which is in the 2, 4, 5, 6, 7 or 9 position, or (b) the two said rings are such that either (i) at least one of them contains at least one further nitrogen atom or (ii) they are fused to another aromatic ring which contains at least one nitrogen atom, and X represents an anionic or neutral coligand.