A NEW-TYPE OF MU(4)-OXO-BRIDGED COPPER TETRAMER - SYNTHESIS, X-RAY MOLECULAR-STRUCTURE, MAGNETISM AND SPECTRAL PROPERTIES OF ORPHOLINOMETHYL)-4-METHYLPHENOLATO)TETRACOPPER(II) AND ORPHOLINOMETHYL)-4-METHYLPHENOLATO)TETRACOPPER(II)

Reaction of CuBr2 or Cu(ClO4)(2).6H(2)O and sodium benzoate with the t ridentate ligand 2,6-bis(morpholinomethyl)-4-methylphenol (Hbmmk) in m ethanol yields two copper complexes [Cu4OBr4(bmmk)(2)].2MeOH (1) and [ Cu4O(OBz)4(bmmk)2] H2O (2). The compounds were characterized by single -crystal X-ray diffraction studies and are shown to contain W-oxo-brid ged cluster compounds of the new type [Cu(4)OX(4)L(6)] 1 crystallizes in the monoclinic space group P2(1)/c with a = 12.693(2) Angstrom, b = 12.378(2) Angstrom, c = 29.293(6) Angstrom, S = 96.32(3)degrees, V = 4574.4 Angstrom(3), and Z = 4. Discrepancy values of R = 0.0324 and R( w) = 0.0309 were obtained for 5544 independent reflections and 517 adj ustable parameters. The complex has a central mu(4)-bridging oxygen su rrounded tetrahedrally by four copper atoms (average Cu-O distance 1.9 17 Angstrom). By copper pairing two of the Cu...Cu distances (average 3.000 Angstrom) are significantly shorter than the other four (average 3.193 Angstrom). The four bromine ligands and the two phenoxo groups of the deprotonated bmmk ligand are in a mu(2)-bridging mode and bridg e each of the Cu...Cu vectors. The structure is completed by four term inal, N-bonded morpholine groups, one of them attached to each of the copper atoms. All copper centers are in trigonal bipyramidal coordinat ion. Crystals of 2 are also monoclinic, space group P2(1), with a = 11 .889(2) Angstrom, b = 20.250(4) Angstrom, c = 12.481(3) Angstrom, beta = 95.12(2)degrees, V = 2992.8 Angstrom(3), and Z = 2. R = 0.0874 and R(w) = 0.0879 for 4792 independent reflections and 776 adjustable para meters. The complex consists of a central Cu4O tetrahedron (average Cu -O = 1.925 Angstrom). As in 1, copper pairing leads in 2 to two short (average 2.992 Angstrom) and four long Cu Cu distances (average 3.216 Angstrom), The bromine ligands of 1 are replaced in 2 by mu(1,3)-bridg ing benzoate groups. The more rigid benzoate framework leads to three different coordination polyhedra around the copper atoms: octahedral f or Cu(1), square planar for Cu(2), and square pyramidal for Cu(3) and Cu(4). Magnetic susceptibility measurements in the temperature range 4 .2-475.4 K indicate significant antiferromagnetic coupling between the copper(II) centers of both complexes. The experimental data were fitt ed to a modified Heisenberg model with two coupling constants J(12) an d J(13) The best least-squares fit parameters were g = 2.19, J(12) = - 296 cm(-1), J(13) = -36 cm(-1), and x(p) = 2.4% for 1 and g = 2.01, J( 12) = -175 cm(-1), J(13) = -18 cm(-1), and x(p) = 0.8% for 2. The susc eptibilities calculated with this model were found to be highly insens itive to J(13) but very sensitive to J(12).