1,1,1-Tris(hydroxymethyl)propane in manganese carboxylate chemistry: synthesis, structure and magnetic properties of a mixed-valence [MnIII4MnII4] cluster featuring the novel [MnIII4MnII4(μ3-OR)6(μ2-OR)8]6+ core

Abstract

The reaction between MnBr₂·4H₂O with H₃tmp (1,1,1-tris(hydroxymethyl)propane) in MeCN in the presence of Na(O₂CCMe₃) and NBu₄Br produces the complex [Mn₈(O₂CCMe₃)₂(tmp)₂(Htmp)₄Br₄(H₂O)₂]·2MeCN (1·2MeCN) in good yield. The centrosymmetric octanuclear molecule consists of four Mn^III and four Mn^II ions assembled together by fourteen alkoxo bridges to give a [Mn^III₄Mn^II₄(μ₃-OR)₆(μ₂-OR)₈]⁶⁺ rod-like core in which the metal centres are arranged in a planar zigzag fashion. Peripheral ligation is provided by a combination of bridging pivalate ions, terminal bromides and water molecules. Dc magnetic susceptibility measurements reveal the presence of dominant antiferromagnetic interactions leading to a spin ground state of S = 0. A rationalization of this result is attempted by structural comparison with previously reported tetranuclear manganese complexes containing the [Mn^III₂Mn^II₂(μ₃-OR)₂(μ₂-OR)₄] core in which the magnetic interactions are ferromagnetic.