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 mu(4), eta(3) -HPO42-CU(II) compounds with an unprecedented mode of a hydrogenphosphato bridge, [CU4(d-pyam) (4)(mu(4), eta(3)-HPO4)(2)(mu-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 mu(4), eta(3) coordination mode which is rarely found in hydrogenphosphate metal compounds. Each (different) pair of Cu(11) ions is additionally bridged by halide ions, with relatively long Cu X distances (2.551(3)-2.604(3) angstrom for 1 and 2.707(1)-2.766(2) angstrom for 2) and subsequently also a small Cu-X-Cu angle (65.7(1)degrees and 65.1(1)degrees for 1 and 61.6(1)degrees and 62.4(1) for 2) and a large Cu X-Cu angle (95.5(1)degrees and 96.5(1)degrees for 1 and 91.1(1)degrees and 92.6(1)degrees for 2). Cu (...) Cu distances in the tetranuclear units varies from 2.802(3) to 5.232(3) angstrom for 1 and from 2.834(1) to 5.233(1) angstrom 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. (c) 2005 Elsevier B.V. All rights reserved.