Tetracarboxylate Ligands as New Chelates Supporting Copper(II) Paddlewheel-Like Structures

Abstract

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