High-Frequency, High-Field EPR; Magnetic Susceptibility; and X-ray Studies on a Ferromagnetic Heterometallic Complex of Diethanolamine (H₂L), [Cu₄(NH₃)₄(HL)₄][CdBr₄]Br₂·3dmf·H₂O

Abstract

The novel heterometallic complex [Cu(4)(NH(3))(4)(HL)(4)][CdBr(4)]Br(2).3dmf.H(2)O has been prepared in the reaction of zerovalent copper with cadmium oxide in the air-exposed solution of ammonium bromide and diethanolamine (H(2)L) in dimethylformamide (dmf). The compound is monoclinic, with space group P2(1)/c, a = 14.876(3) A, b = 33.018(6) A, c = 11.437(2) A, beta = 108.182(3)(o), and Z = 4. The crystal lattice consists of [Cu(4)(NH(3))(4)(HL)(4)](4+) cations, [CdBr(4)](2)(-), Br(-) anions, and uncoordinated dmf and water molecules. In the cation, four independent Cu atoms occupy vertexes of a distorted tetrahedron with bridged Cu...Cu distances in the range 3.127(2)-3.333(3) A and other Cu...Cu separations being 3.445(3)-3.503(2) A. 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 muB 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.