1,1,1-Tris(hydroxymethyl)propane in manganese carboxylate chemistry:synthesis,structure and magnetic properties of a mixed-valence [Mn~(III)_4 Mn~(II)_4] cluster featuring the novel [Mn~(III)_4Mn~(II)_4(mu_3-OR)_6(mu_2-OR)_8]~(6+) core

摘要

The reaction between MnBr_2 centre dot 4H_2O with H_3tmp (1,1,1-tris(hydroxymethyl)propane) in MeCN in the presence of Na(O_2CCMe_3) and NBu_4Br produces the complex [Mn_8(O_2CCMe_3)_2(tmp)_2(Htmp)_4Br_4-(H_2O)_2]centre dot 2MeCN (1 centre dot 2MeCN) in good yield.The centrosymmetric octanuclear molecule consists of four Mn? and four Mn" ions assembled together by fourteen alkoxo bridges to give a [Mn~(III)_4Mn~(II)_4(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 [Mn~(III)_2Mn~(II)_2(mu_3-OR)_2(mu_2-OR)_4] core in which the magnetic interactions are ferromagnetic.