Mn/Ce clusters from the use of pivalate and chelate ligands: Mn ^III₈Ce^IV, Mn^III₂Ce ^IV₂, and Mn^III₄Ce^III ₂ products

The reaction system Mn^II/Ce^III/IV/(CH ₃)₃CCO₂^- has been investigated and has yielded four Mn_xCe_y and one Mn^III ₄ compounds. Reactions in the presence of NBuⁿ ₄MnO₄ afforded a Mn^III₈Ce ^IV compound [Mn₈CeO₈(Bu^tCO ₂)₁₂(DMF)₄] (1), consisting of a Ce ^IV atom inside a loop of eight Mn^III ions. Reactions also containing 1,10-phenanthroline (phen) or 2,2′-bipyridine (bpy) gave [Mn₂Ce₂O₂(OH)₂(Bu^tCO ₂)₄(NO₃)₄(phen)₂] (2) or [Mn₂Ce₂O₂(OH)₂(Bu^tCO ₂)₄(NO₃)₄(bpy)₂] (3), respectively, containing the Mn^III₂Ce^IV ₂O₂ core. In contrast, reactions in the presence of 2-(hydroxymethyl)pyridine (hmpH) yielded the Mn^III₄Ce ^III₂ cluster [Mn₄Ce₂O ₂(Bu^tCO₂)₅(NO₃) ₅(hmp)₄] (4), with an unprecedented [Mn₄Ce ₂(μ₄-O)₂] core, and a homometallic, butterfly-like Mn^III₄ cluster [Mn₄O ₂(Bu^tCO₂)₆(pic)₂(H ₂O)₂] (5), in which oxidation of hmp^- to picolinate (pic^-) has occurred. Variable-temperature, dc and ac measurements were performed on polycrystalline samples of 1-5. Fitting of the obtained magnetization (M) versus field (H) and temperature (T) data by matrix diagonalization, and including only axial anisotropy (zero-field splitting, ZFS), gave a ground state spin of S = 5 for 1·2DMF. The magnetic susceptibility data for 2·2Et₂O and 3 up to 300 K were fit and revealed very weak ferromagnetic interactions between the Mn^III ions; J = +0.5(2) cm^-1 for 2·2Et₂O, and J = +0.3(1) cm^-1 for 3. Complexes 4·3MeCN and 5·2Bu ^tCO₂H have S = 0 ground states.