Synthesis, crystal structures and selective oxygenation of dinuclear copper(II) complexes of N,N,N′,N′-xylylenediamine tetraacetate

Two dinuclear copper(II) complexes, [Cu2L1(imH)2(H2O)2] · 4H2O (1) and [Cu2L2(imH)2(H2O)2] · 2H2O (2) (L1H4 = N,N,N′,N′-m-xylylenediamine tetraacetic acid, L2H4 = N,N,N′,N′-p-xylylenediamine tetraacetic acid, imH = imidazole), were synthesized aiming at exploring the geometry of the flexible ligands on their complex structures and reactions with H2O2. In complex 1, both Cu(II) ions are five-coordinated with square-pyramidal geometry and water molecules occupy the apical position. The Cu···Cu distance is 5.344(7) Å. Complex 2 adopts the same coordination geometry as that in 1. The Cu···Cu distance is 7.812(5) Å. Complex 1 exhibits hydroxylation of the xylyl linker of the supporting ligand in the presence of H2O2 in aqueous solution. No observable reaction took place under the identical conditions for complex 2. Proximity effect of the metal center is responsible for the hydroxylation.