Tetracarboxylate ligands as new chelates supporting copper(II) paddlewheel-like structures

Two new ligands N,N,N',N'-tetrakis(2-methylbenzoic acid)-1,4-diaminomethylbenzene, 5H4, and N,N,N',N'-tetrakis(2-methylbenzoic acid)-4,4'-diaminomethyldiphenyl, 6H4, carrying four carboxylate groups suitable for bridging dinuclear centers have been prepared and their paddlewheel complexes with copper(II) prepared. The phenyl-bridged ligand 5H4 gives a cyclic octanuclear species [(Cu2)4(5)4], while the diphenyl-bridged ligand 6H4 gives a lantern-like tetranuclear species [(Cu2)2(6)2]; both were characterized by X-ray crystallography. If the amine functions of 5 are protonated, intramolecular hydrogen bonds position the four carboxylates in such a way as to allow formation of the unusual compound [Cu4(5H2)2Cl](3+) in which a Cu4 square centered by a chloro ligand is sandwiched between two (5H2)(2-) ligands. The magnetic properties of this compound have been studied and show antiferromagnetic coupling between adjacent coppers (J = -33.7 cm(-1)).