A Ferromagnetically Coupled CrCu₃ Tetramer and GdCu₄ Pentamer with a [15]N₄ Macrocylic Ligand Incorporating an Oxamido Bridge

The synthesis and structural and magnetic properties of heteropolynuclear complexes [(L3Cu)3Cr](CH3CN)3(ClO4)3 (2) and [(L3Cu)4Gd·H2O](CH3OH)(H2O)(ClO4)3 (3) (H2L3 ligand is 2,3-dioxo-5,6:14,15-dibenzo-1,4,8,12-tetraazacyclo-pentadeca-7,12-diene) and their precursor L3Cu (1) are presented. Complex 2 crystallizes in space group P21/n with cell parameters a = 20.828(6) Å, b = 18.321(5) Å, c = 7.578(5) Å, α = 90°, β = 91.990(8)°, γ = 90°, and Z = 4. The CrIII center is coordinated by six oxygen atoms from three CuII precursors. The Cr−O bonds range over 1.948−1.982 Å. The coordination environments of all the terminal CuII ions change in comparison with their CuII 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 P1̄ with cell parameters a = 14.805(4) Å, b = 16.882(5) Å, c = 17.877(5) Å, α = 75.403(5)°, β = 83.317(6)°, γ = 70.600(5)°, and Z = 2. The central GdIII assumes an 8 + 1 coordination environment, namely eight oxygen atoms from four CuII precursors and one oxygen atom from H2O. The fit of the experimental data gives J = 0.27(2) cm-1, gGd = 1.98(1), and gCu = 2.05(1). This small and positive J value shows weak ferromagnetic interaction between metal ions.