Synthesis, structure, and magnetic properties of two new ferromagnetic/antiferromagnetic one-dimensional nickel(II) complexes. Magnetostructural correlations

Two new one-dimensional nickel(II) complexes were synthesized and character ized: [Ni(N,N-dimethylethylene-diamine)(N-3)(2)] (1) and [Ni(2-aminoethylpy ridine)(N-3)(2)] (2). The crystal structuresof 1 and 2 were solved. Complex 1 crystallizes in the monoclinic system, space group P2(1)/n with a = 10.5 69(2) Angstrom, b = 7.331(4) Angstrom, c = 12.9072-(8) Angstrom, beta = 111 .324(10)degrees, and Z = 4. Complex 2 crystallizes in the monoclinic system , space group P2(1)/c with a 12.299(5) Angstrom, b = 14.307(2) Angstrom, c = 12.603(3), beta = 106.72(2)degrees, and Z = 4. The two complexes are simi lar and may be described as one-dimensional systems with double-azido-bridg ed ligands in end-to-end and end-on coordination alternatively. The end-on moiety is almost identical for 1 and 2, but the end-to-end moiety is differ ent in each structure: for 1 this part is almost planar but for 2 is nonpla nar. In both cases the Ni atoms are situated in similar distorted octahedra l environments. The magnetic properties of the two compounds were studied b y susceptibility measurements vs temperature. The chi(M) vs T plots for 1 a nd 2 show a global antiferromagnetic behavior with a maximum near room temp erature for 1 and at very low temperature for 2 J(1) values for 1 and 2 wer e deduced from the spin Hamiltonian -Sigma(J(1)S(i)S(i+1) + J(2)S(i+1)S(i+2 )) The computational method was based on the numerical solution for finite systems of increasing size. J values for 1 were (J1) = -187 cm(-1) and J(2) = +77 cm(-1) and for 2 J(1) = -28 cm(-1) and J(2) = +73 cm(-1). The positi ve values correspond to end-on azido ligands and the negative values to end -to-end azido ligands. Since the geometries of the [Ni(N-3)](2) moieties in volving che end-on azido liands are almost the same in the two structures, the ferromagnetic coupling is nearly identical in the two compounds, while the significantly different antiferrornagnetic couplings reflect the Dear p lanarity of the endto-end Ni-2(N-3)(2) fragment in 1 and its twisted geomet ry in 2.