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 [(LCu)3Cr](C(H)3CN)3(C1(0)4)3 (2) and [(L3Cu)4Gd-(H)20](C(H)30H)((H)20)(CIC)4)3 (3) ( ligand is 2,3-dioxo-5,6:14,15-dibenzo-1,4,8,12-tetraazacyclopentadeca-7,12-diene) and their precursor LCu (1) are presented. Complex 2 crystallizes in space group P2n with cell parameters a = 20.828(6) A, b - 18.321(5) A, c = 7.578(5) A, a = 90°, (beta) = 91.990(8) y = 90°, and Z= 4. The Crʹ" center is coordinated by six oxygen atoms from three Cu" precursors. The Cr-O bonds range over 1.948-1.982 A. The coordination environments of all the terminal Cu" ions change in comparison with their Cu" precursor. The ferromagnetic coupling (J = 16.48(1) cm) 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 PI with cell parameters a = 14.805(4) A, b = 16.882(5) A, c = 17.877(5) A, a = 75.403(5)°, (beta) = 83.317(6)°, y = 70.600(5)°, and Z = 2. The central Gd"ʹ assumes an 8 + 1 coordination environment, namely eight oxygen atoms from four Cu" precursors and one oxygen atom from hO. The fit of the experimental data gives J = 0.27(2) cm~, g = 1.98(1), and g = 2.05(1). This small and positive J value shows weak ferromagnetic interaction between metal ions.