High-frequency, high-field EPR; Magnetic susceptibility; and x-ray studies on a ferromagnetic heterometallic complex of diethanolamine (H2L), [Cu-4(NH3)(4)(HL)(4)][CdBr4]Br-2 center dot 3dmf center dot H2O

摘要

The novel heterometallic complex [Cu-4(NH3)(4)(HL)(4)][CdBr4]Br-2.3dmf.H2O has been prepared in the reaction of zerovalent copper with cadmium oxide in the air-exposed solution of ammonium bromide and diethanolamine (H2L) in dimethylformamide (dmf). The compound is monoclinic, with space group P2(1)/c, a = 14.876(3) Angstrom, b = 33.018-(6) Angstrom, c = 11.437(2) Angstrom, beta = 108.182(3)degrees, and Z = 4. The crystal lattice consists of [CU4(NH3)(4)(HL)(4)](4+) cations, [CdBr4](2-), Br- anions, and uncoordinated dmf and water molecules. In the cation, four independent Cu atoms occupy vertexes of a distorted tetrahedron with bridged (CuCu)-Cu-... distances in the range 3.127(2)-3.333(3) Angstrom and other (CuCu)-Cu-... separations being 3.445(3)-3.503(2) Angstrom. The magnetic susceptibility and the EPR spectra were measured over the temperature ranges 1.8-300 and 3-300 K, respectively. The magnetic moment was found to increase with decreasing temperature to reach a maximum of 2.60 mu(B) per one copper atom at ca. 10 K and was found, subsequently, to diminish slightly at lower temperatures owing to zero-field and Zeeman splitting of the S = 2 ground state. The temperature dependence of the magnetic susceptibility was fitted to the spin Hamiltonian H = J(ab)S(a)S(b) + J(bc)S(b)S(c), + J(cd)S(c)S(d), + J(ad)S(a)S(d) J(ac)S(a)S(c) + J(bd)S(b)S(d) with the exchange integrals J(ab) = J(bc), = J(cd) = J(ad) = -65(3) cm(-1) and J(ac) = J(bd) = + 1(3) cm(-1). High-field, high-frequency (95-380 GHz) EPR spectra due to an S = 2 ground state were simulated with g(x) = 2.138(1), g(y) = 2.142(1), g(z) = 2.067(1), D = -0.3529(3) cm(-1), and E = -0.0469(8) cm(-1). Calculations based on the X-ray structure indicate a negligible contribution of the magnetic dipole-dipole interactions to the zfs parameters D and E. A discussion of the isotropic and anisotropic exchange interactions and their effect on the zfs parameters is also given.