1,1,1-tris(hydroxymethyl)propane in manganese carboxylate chemistry: synthesis, structure and magnetic properties of a mixed-valence [(Mn4Mn4II)-Mn-III] cluster featuring the novel [(Mn4Mn4II)-Mn-III(mu(3)-OR)(6)(mu(2)-OR)(8)](6+) core

The reaction between MnBr(2)center dot 4H(2)O with H(3)tmp (1,1,1-tris(hydroxymethyl)propane) in MeCN in the presence of Na(O2CCMe3) and NBu4Br produces the complex [Mn-8(O2CCMe3)(2)(tmp)(2)(Htmp)(4)Br-4-(H2O)2]center dot 2MeCN (1 center dot 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 [(Mn4Mn4II)-Mn-III(mu(3)-OR)(6)(mu(2)-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 [(Mn2Mn2II)-Mn-III(mu(3)-OR)(2)(mu(2)-OR)(4)] core in which the magnetic interactions are ferromagnetic.