SYNTHESIS, STRUCTURE AND MAGNETIC-PROPERTIES OF TRINUCLEAR COMPLEXES OF COPPER(II) WITH DIFFERENT AMINES AS TERMINAL LIGANDS

Three new trinuclear copper(II) complexes were synthesized: {[(ettmd)Cu]2[mu-Cu(pba)]}(ClO4)2 (1), {[(pmd)Cu]2[mu-Cu(Me2pba)]}(ClO4)2 . 3H2O (2) and {[(bapa)Cu]2[mu-Cu(Me2pba)]}ClO4)2 (3) where Cu(pba) = 1,3-propanediyl-bis(oxamato)cuprate(II), Cu(Me2pba) = 2,2-dimethyl-1,3-propanediyl-bis(oxamato)cuprate(II), ettmd = 4-ethyl-1,1,7,7-tetramethyldiethylenetriamine; pmd = N,N,N',N'', N''-pentamethyldiethylenetriamine, bapa = bis(3-aminopropyl)amine. The structures of compounds 1, 2 and 3 were determined by X-ray analysis. The crystals of 1 are monoclinic, space group P2(1)/c, with a = 18.463(4), b = 14.402(3), c = 16.537(4) angstrom, beta = 109.00(3)degrees, Z = 4 and R = 0.072 for 2447 reflections observed. The crystals of 2 are triclinic, space group PT, with a = 19.610(4), b = 16.626(4), c = 16.007(3) angstrom, alpha = 115.75(3)degrees, beta = 89.97(3)degrees, gamma = 100.86(4)degrees, Z = 4 and R = 0.068 for 7342 reflections observed. The crystals of 3 are orthorhombic, space group Pcba, a = 40.492(4), b = 16.363(3), c = 10.944(3) angstrom, Z = 8 and R = 0.034 for 1634 reflections observed. The central copper(II) ions of compounds 1 and 2 are square-pyramidal, the apical positions being occupied by a perchlorate anion. In 3 the central copper ion is- square-planar. The terminal copper ions of compounds 1, 2 and 3 are all pentacoordinated with geometries that are intermediate between square-pyramidal and trigonal-bipyramidal. If the coordination is described in terms of square-pyramidal geometry, the basal plane of each terminal copper atom is approximately perpendicular to the basal plane of the central copper ion. The distortion towards trigonal-bipyramidal geometry is largest for compound 1 and smallest for 3. Magnetic susceptibility measurements were carried out for this series of complexes. The magnetic data were interpreted using the Heisenberg Hamiltonian and led to J values of -137.1, -128.1 and -92.1 cm-1 for 1, 2 and 3, respectively. The intensity of the magnetic coupling is discussed in terms of the relative orientation of magnetic orbitals.