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†
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 MnIII and four MnII ions assembled together by fourteen alkoxo bridges to give a [MnIII4MnII4(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 [MnIII2MnII2(μ3-OR)2(μ2-OR)4] core in which the magnetic interactions are ferromagnetic.