Trinuclear Cu^IIM^IICu^II complexes of an oxamide/dioxime ligand and extension to a bimetallic magnetic compound

N,N′-Bis[2-(hydroxyiminomethyl)phenyl]oxamide (H₄L) provided trinuclear Cu^IIM^IICu^II complexes [M{Cu(HL)-(DMF)}₂(DMF)₂] (M^II = Mn 1, Co 2, Ni 3 or Zn 4). The crystal structures of 1-4 have been determined by X-ray crystallography. They are isomorphous and have an oxamidate-bridged trinuclear Cu^IIM^IICu^II structure. The Cu^II resides in a pseudo-macrocyclic framework of (HL)^3- comprised of an oxamidate and a hydrogen-bonded dioximate (=N-O⋯H⋯O-N=) groups to form a square-pyramidal structure {Cu(HL)(DMF)} together with a DMF molecule. Two {Cu(HL)(DMF)} entities co-ordinate to a Mn^II through the oxamidate oxygens to afford a cis octahedral environment about the metal together with two DMF oxygens. The Cu^II⋯M^II intermetallic distance separated by the oxamidate bridge is 5.33-5.49 Å. In the case of 1 and 3 a significant antiferromagnetic interaction operates between the adjacent Cu^II and M^II. The reaction of 1 with Mn^II in acetonitrile in the presence of KOH and 18-crown-6 formed Mn{Cu(L)}(H₂O)₄ that has a polymeric structure extended by the dioximate-Mn^II-dioximate linkage. It is a weak ferromagnet (T_C = 5.5 K) exhibiting a weak antiferromagnetic interaction between the ferrimagnetic chains.