 This bonding can best be described by a covalent single bond with an overlaying share of polar bonding.The μ2-N-bridging mode arises when the free electron pair at nitrogen gives rise to dimerization.These dimeric complexes yield different M-N bond lengths depending on the ligands present in the rest of the ligand sphere of M. When the complex contains two or four identical ligands, nearly equal M-N distances are observed, whereas, when different or odd-numbered identical ligands are in the complex, the M-N distances are all of significantly different length.