Tetra-, tetradeca- and octadecametallic clusters of Mn

Abstract

Reaction of equimolar amounts of MnBr2·4H2O and HL1 ((3,5-dimethyl-1H-pyrazol-1-yl)methanol) in a basic MeCN solution leads to the formation of [MnII4(L1)4Br4(H2O)4] (1), whose metallic skeleton is a [MnII4] tetrahedron and cluster core a [MnII4(μ3-O)4] cubane. Replacing MnBr2·4H2O with Mn(O2CMe)2·4H2O affords [MnIII2MnII12O2(L1)4(OAc)22] (2) which is best described as a series of edge-sharing [Mn4] tetrahedra that have self-assembled into a linear array in which each [Mn2] pair is ‘twisted’ with respect to its neighbours in a corkscrew-like manner. Employment of the triangle [MnIII3O(OAc)6(py)3](ClO4) as a reactant instead of a MnII salt results in the formation of [MnIII14MnII4O14(L1)4(HL1)2(OAc)18(H2O)2] (3) whose core is comprised of three vertex-sharing [MnIII4] butterflies flanked on either side by one [MnIII4] cubane and one [MnIII2MnII2] tetrahedron. Dc magnetic susceptibility and magnetisation measurements of polycrystalline samples of 1-3 reveal the predominance of antiferromagnetic exchange interactions. For [Mn4] (1) this leads to a diamagnetic ground state, while for [Mn18] (3) competing exchange interactions result in Single-Molecule Magnet (SMM) behaviour with Ueff = 22 K.