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 View the MathML sourceμ4,η3-HPO42-Cu(II) compounds with an unprecedented mode of a hydrogenphosphato bridge, [Cu4(dpyam)4(μ4,η3-HPO4)2(μ-X)2]2+ (in which dpyam = di-2-pyridylamine and X = Cl (1), Br (2)) have been synthesised and characterised structurally and magnetically. The Cu(II) ions in the structures 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, with relatively long Cu–X distances (2.551(3)–2.604(3) Å for 1 and 2.707(1)–2.766(2) Å for 2) and subsequently also a small Cu–X–Cu angle (65.7(1)° and 65.1(1)° for 1 and 61.6(1)° and 62.4(1) for 2) and a large Cu–X–Cu angle (95.5(1)° and 96.5(1)° for 1 and 91.1(1)° and 92.6(1)° for 2). Cu⋯Cu distances in the tetranuclear units varies from 2.802(3) to 5.232(3) Å for 1 and from 2.834(1) to5.233(1) Å in 2. The lattice structures are stabilised by extensive intermolecular hydrogen bonds. The magnetic susceptibility measurements down to 5 K revealed a weak ferromagnetic interaction between the outer pairs of 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.