Linear Tetranuclear Copper(II) Complexes with Bridging Methoxide and a Schiff-Base Ligand: The Preparation and Magnetic Study of the [Cu(salpd-μ-<i>O</i>,<i>O</i>′)(μ-L)Cu(μ-CH3O)2Cu(μ-L)(sapd-μ-<i>O</i>,<i>O</i>′)Cu] Complexes (and L=Acetate or Formate Ions) and the Structure Determination of the Complex with L=Acetate

Abstract

Abstract The title complexes have been synthesized in quantitative yield from [Cu(salpd)] and copper(II) acetate or copper(II) formate , where H2salpd represents N,N′-disalicylidene-1,3-propanediamine. [Cu(salpd-μ-O,O′)(μ-L)Cu(μ-CH3O)2Cu(μ-L)(salpd-μ-O,O′)Cu] crystallizes in the monoclinic space group P21/n with formula=Cu4C40H44N4O10, F.W.=995.0, a=11.826(2) Å, b=17.192(4) Å, c=9.836(2) Å, β=94.08(2)°, V=1994.8(7) Å3 and Z=2 (R=3.83%), where L=CH3COO. The complex forms a centrosymmetric molecule made up of two units of [Cu(salpd-μ-O,O′)(μ-CH3COO)Cu] bound by a pair of methoxo bridges; each terminal copper(II) ion forms four short bonds with N and O atoms of salpd and a slightly longer (2.235(4) Å) axial bond with one of the oxygens of the acetato group, whereas each inner copper(II) ion is also pyramidally coordinated by two methoxo oxygens, one of the acetato oxygens, and one of the bridging salpd oxygens, the distant axial position being occupied (Cu–O=2.323(3) Å) by the remaining bridging salpd oxygen. The magnetic susceptibilities of the complexes in the 86.8–299.0 K range have been analyzed on the basis of a four-spin model for the linear copper(II) complexes, and the values of g and Jij, based on the Heisenberg-type Hamiltonian H=−2ΣJijSi·Sj, have been estimated as g (average)=2.13, J12=−390 cm−1, J13=67 cm−1 and J14=34 cm−1 in the complex with acetate bridges, and as g (average)=2.20, J12=−263 cm−1, and J13=39 cm−1 and J14=J34=0 cm−1 in the complex with formate bridges, where the numbering refers to the 3–1–2–4 arrangement of the Cu2+ ions.