Synthesis and magnetic properties of heterometal cyclic tetranuclear complexes [Cu^IILM^II(hfac)]₂ (M^II = Zn, Cu, Ni, Co, Fe, Mn; H₃L = 1-(2-hydroxybenzamido)-2-((2-hydroxy-3-methoxybenzylidene)amino)ethane; Hhfac = hexafluoroacetylacetone)

A series of heterometal cyclic tetranuclear complexes [Cu ^IILM^II(hfac)]₂ (M^II = Zn (1), Cu (2), Ni (3), Co (4), Fe(5), and Mn (6)) have been synthesized by the assembly reaction of K[CuL] and [M^II(hfac)₂(H₂O) ₂] with a 1:1 mole ratio in methanol, where H₃L = 1-(2-hydroxybenzamido)-2-((2-hydroxy-3-methoxybenzylidene)amino)ethane and Hhfac = hexafluoroacetylacetone. The crystal structures of 2, 4, and [Cu ^IILMn^II(acac)]₂ (6a) (Hacac = acetylacetone) were determined by single-crystal X-ray analyses. Each complex has a cyclic tetranuclear Cu^II₂M^II₂ structure, in which the Cu^II complex functions as a "bridging ligand complex", and the Cu^II and M^II ions are alternately arrayed. One side of the planar Cu^II complex coordinates to one M" ion at the two phenoxo and the methoxy oxygen atoms, and the opposite side of the Cu^II complex coordinates to another M" ion at the amido oxygen atom. The temperature-dependent magnetic susceptibilities revealed spin states of S_M = 0, 1/2, 1, 3/2, 2, and 5/2 for the Zn ^II, Cu^II, Ni^II, Co^II, Fe ^II, and Mn^II ions, respectively. Satisfactory fittings to the observed magnetic susceptibility data were obtained by assuming a rectangular arrangement with two different g-factors for the Cu^II and M^II ions, two different isotropic magnetic exchange interactions, J₁ and J₂, between the Cu^II and M ^II ions, and a zero-field splitting term for the M^II ion. In all cases, the antiferromagnetic coupling constants were found for both exchange interactions suggesting nonzero spin ground states with S_T = 2|S_M - S_Cu|, which were confirmed by the analysis of the field-dependent magnetization measurements.