Synthesis and characterization of a series of manganese phosphonate complexes with various valences and nuclearity

Abstract

A series of new manganese phosphonate clusters with unprecedented topologies, [Mn₂₀Na₄O₁₂(t-BuPO₃)₁₂(O₂CMe)₁₆(H₂O)₁₂]·5H₂O (1), [Mn₁₅O₆(MePO₃)₂(MeCOO)₁₈(H₂O)₁₂][MePO₃H]₂·12H₂O (2), and [Mn(t-BuPO₃H)₂(phen)₂]·MeCOOH (3) have been synthesized and characterized. The core of 1 is composed of two folded “butterfly-like” [Mn₄(μ₃-O)₂] units and two trigonal prism [Mn₆O₆] units connected by four μ₃-O, resulting in a twisted oval of twenty homovalent manganese(III) ions. The pentadecanuclear core of complex 2 is mixed-valent, containing six Mn^III and nine Mn^II ions and features six μ₄-O and two capping MePO₃²⁻ anions adopting the binding mode [6.222], forming a rudder-like cage structure with a chiral D₃ symmetry. Compound 3 is a manganese(II) phosphonate and features a 1D chain configuration packed by hydrogen bonds and π–π stacking interactions. Magnetic susceptibility measurements reveal that compounds 1, 2 and 3 display antiferromagnetic interactions between the adjacent manganese ions, while the in-phase signal χ′_MT and out-of-phase signal χ″_M of complex 1 exhibit frequency-dependence below approximately 3 K, but no frequency-dependence is observed in the ac signals of complex 2.