Inorganic Chemistry, Vol.42, No.5, 1462-1466, 2003
A ferromagnetically coupled CrCu3 tetramer and GdCu4 pentamer with a [15]N-4 macrocylic ligand incorporating an oxamido bridge
The synthesis and structural and magnetic properties of heteropolynuclear complexes [((LCu)-Cu-3)(3)Cr](CH3CN)(3)(ClO4)(3) (2) and [(L3Cu)(4)Gd.H2O](CH3OH)(H2O)(ClO4)(3) (3) (H2L3 ligand is 2,3-dioxo-5,6:14,15-dibenzo-1,4,8,12-tetraazacyclopentadeca-7,12-diene) and their precursor L3Cu (1) are presented. Complex 2 crystallizes in space group P2(1)/n with cell parameters a = 20.828(6) Angstrom, b = 18.321(5) Angstrom, c = 7.578(5) Angstrom, alpha = 90degrees, beta = 91.990(8)degrees, gamma = 90degrees, and Z = 4. The Cr-III center is coordinated by six oxygen atoms from three Cull precursors. The Cr-O bonds range over 1.948-1.982 Angstrom. The coordination environments of all the terminal Cu-II ions change in comparison with their Cu-II precursor. The ferromagnetic coupling (J = 16.48(1) cm(-1)) observed for 2 can be rationalized by symmetry considerations. For any pair of interacting magnetic orbitals, strict orthogonality is obeyed and the interaction is ferromagnetic. Complex 3 crystallizes in space group P1 with cell parameters a = 14.805(4) Angstrom, b = 16.882(5) Angstrom, c = 17.877(5) Angstrom, alpha = 75.403(5)degrees, beta = 83.317(6)degrees, gamma = 70.600(5)degrees, and Z = 2. The central Gd-III assumes an 8 + 1 coordination environment, namely eight oxygen atoms from four Cull precursors and one oxygen atom from H2O. The fit of the experimental data gives J = 0.27(2) cm(-1), g(Gd) = 1.98(1), and g(Cu) = 2.05(1). This small and positive J value shows weak ferromagnetic interaction between metal ions.