A novel tetranuclear hydrogenphosphate-bridged Cu(II) cluster. Synthesis, structure, spectroscopy and magnetism of [Cu4(dpyam)4(μ4,η3-HPO4)2(μ-X)2]X2(H2O)6 (X = Cl, Br)

Two novel tetranuclear μ4,η3-HPO42-Cu(II) compounds with an unprecedented mode of a hydrogenphosphato bridge, [Cu4(dpyam)4(μ4,η3-HPO4)2(μ-X)2]2+ X = Cl (1), Br (2) have been synthesised and characterised. The Cu(II) ions each display a square-pyramidal geometry, with two tridentate hydrogenphosphato groups bridging four copper atoms in a μ4,η3 coordination mode which is rarely found in hydrogenphosphate metal compounds. Each (different) pair of Cu(II) ions is additionally bridged by halide ions. The magnetic susceptibility measurements down to 5 K revealed a weak ferromagnetic interaction between the outer Cu(II) ions which vary from 22 to 46 cm−1 in 1 and 12 to 33 cm−1 in 2 and a moderately strong antiferromagnetic interaction between the inner Cu(II) ions of −79 cm−1 in 1 and −83 cm−1 in 2, via the Cu-O-P-O-Cu pathway.