Dodenuclear [Mn III8Ln III4] clusters with 2-(hydroxymethyl)pyridine: syntheses, structures, and magnetic properties

Abstract

A new family of isostructural Mn/Ln dodenuclear clusters: [Mn₈Ln₄(O)₈(hmp)₄(O₂CPh)₁₂(NO₃)₄(PhCO₂H)(C₂H₅OH)] [Ln = La (1), Pr (2), Nd (3), Gd (4), Dy(5), hmpH = 2-(hydroxymethyl)pyridine] have been synthesized by the reaction of Mn(NO₃)₂ and Ln(NO₃)₃·6H₂O with hmpH and benzoic acid as co-ligands. Compounds 1–5 possess a spindle-shaped core of [Mn^III₈Ln^III₄(μ₄-O)₄(μ₃-O)₄(μ₃-OR)₂(μ₂-OR)₈]¹⁰⁺, which is composed of six face-sharing defected cubane units and two square-pyramidal units. The compounds represent the highest nuclearity Mn/Ln clusters with the use of hmpH to date. That the ferromagnetic interactions dominated within complexes 1–4 were suggested by solid-state dc magnetic susceptibility analyses. Compound 4 displays a magnetic-caloric effect (MCE) with 13.94 J kg⁻¹ K⁻¹ as the entropy change at 6 K for ΔH = 8 T. Compounds 1 and 5 exhibit an out-of-phase χ′′_M peak maximum above 2.0 K. Fitting of the ac susceptibility data to an Arrhenius law gives an energy barrier U_eff = 6.88/7.44 K for compounds 1 and 5 respectively.