Two isomeric [Mn12O12(OMe)2(O 2CPh)16(H2O)2]2- single-molecule magnets and a MnIII polymer prepared by a reductive aggregation synthetic route

Abstract

We describe a new synthetic procedure in Mn cluster chemistry involving reductive aggregation of permanganate (MnO4-) ions in MeOH/benzoic acid solution and the first two products that were obtained from this procedure. The first one is the anion [Mn12O12(OMe)2(O 2CPh)16(H2O)2]2- which was isolated as a black microcrystalline material when the solution was left at room temperature overnight. The microcrystalline material was recrystallized from CH2Cl2/hexanes and gave the above mentioned anion as a mixture of two crystal forms (NnBu4)2[Mn 12O12(OMe)2(O2CPh) 16(H2O)2]·2H2O· 4CH2Cl2 and (NnBu4) 2[Mn12O12(OMe)2(O 2CPh)16(H2O)2]·2H 2O·CH2Cl2. The anion contains a central [MnIV4(μ3-O)2(μ-O)2(μ-OMe)2]6+unit surrounded by a non-planar ring of eight MnIII atoms that are connected to the central Mn4 unit by eight bridging μ3-O2- ions. This anion is remarkably similar to the well known [Mn12O12(O 2CR)16(H2O)4] complexes (hereafter called "normal [Mn12]"), with the main difference being the structure of the central cores. The second compound was the polymeric [Mn(OMe)(O2CPh)2]n that was obtained when the solution was left at room temperature for ∼2 weeks. The compound contains a linear chain of repeating [MnIII(μ-O2CPh) 2(μ-OMe)MnIII] units. The chains are parallel to each other and are interacting weakly through π-stacking between the benzoate rings of different chains. Variable temperature ac magnetic measurements and hysteresis studies revealed that both anions are SMMs and like normal [Mn 12] clusters, display both faster- and slower-relaxing magnetization dynamics that we assign to the presence of JT isomerism. Variable temperature magnetic susceptibility studies establish that the MnIII centers of the polymer are antiferromagnetically coupled resulting in a diamagnetic ground state. © 2005 Elsevier Ltd. All rights reserved.