Tetranuclear Homo- and Heterometallic Manganese(III) and Nickel(II) Complexes: Synthesis, Structure, and Magnetic Studies

Three new polynuclear cluster complexes were synthesized and characterized using single-crystal X-ray measurements, infrared spectroscopy, and elemental analyses. A Schiff-base, 2-{[(1-hydroxybutan-2-yl)imino]methyl}phenol (himpH₂), synthesized in situ from the reaction of salicylaldehyde and (±)-2-aminobutanol, was used as ligand. Reactions of the ligand with different Mn^II and Ni^II salts led to two homometallic complexes and a heterometallic complex with [Mn^III₄] (1), [Ni^II₄] (2), and [Mn^III₂Ni^II₂] (3) cores exhibiting square, cubane-type, or butterfly arrangement, respectively. Analysis of the temperature dependence of the magnetic susceptibility of compounds 1–3, using appropriate spin Hamiltonians, indicated that the [Mn^III₄] and [Ni^II₄] compounds show dominant ferromagnetic coupling of the spin carriers, whereas the [Mn₂Ni₂] compound has antiferromagnetic Mn^III–Ni^II and ferromagnetic Ni^II–Ni^II interactions, with a spin ground state S_t = 2. Analyses of the magnetization data in 0–5 T fields at 2 K indicate the presence of positive zero-field splitting (ZFS) values, which is consistent with the absence of slow magnetic relaxation.