A ferromagnetically coupled CrCu3 tetramer and GdCu4 pentamer with a [15]N4 macrocylic ligand incorporating an oxamido bridge.

Abstract

The synthesis and structural and magnetic properties of heteropolynuclear complexes [(L(3)Cu)(3)Cr](CH(3)CN)(3)(ClO(4))(3) (2) and [(L(3)Cu)(4)Gd.H(2)O](CH(3)OH)(H(2)O)(ClO(4))(3) (3) (H(2)L(3) ligand is 2,3-dioxo-5,6:14,15-dibenzo-1,4,8,12-tetraazacyclo-pentadeca-7,12-diene) and their precursor L(3)Cu (1) are presented. Complex 2 crystallizes in space group P2(1)/n with cell parameters a = 20.828(6) A, b = 18.321(5) A, c = 7.578(5) A, alpha = 90 degrees, beta = 91.990(8) degrees, gamma = 90 degrees, and Z = 4. The Cr(III) center is coordinated by six oxygen atoms from three Cu(II) precursors. The Cr-O bonds range over 1.948-1.982 A. 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) A, b = 16.882(5) A, c = 17.877(5) A, 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 Cu(II) precursors and one oxygen atom from H(2)O. 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.