Unusual Mn-5 cluster with a 'twisted bow-tie' topology and (MnMn2Mn2IV)-Mn-II-Mn-III oxidation states: Synthesis, structure, and magnetic properties

The `reductive aggregation' procedure involving the reaction of MnO4- in MeOH in the presence of a carboxylic acid has been extended for the first time to the use of a dicarboxylic acid and the additional presence of a chelate, namely phthalic acid (phthH(2)) and 2,2'-bipyridine (bpy), respectively. The MnO4- : phthH(2):bpy = 1:2:1 reaction in MeOH has led to isolation of [Mn5O4(phth)(3)(phthH)(bpy)(4)](phthH(2)) (phthH) (1), whose Mn5 cation possesses a 'twisted bow-tie' topology comprising two near-perpendicular Mn-3(II,III,IV) scalene triangles fused at the Mn-II ion. Each triangle is bridged by a central mu(3)-O2- and a mu(2)-O2- on the (MnMnIV)-Mn-III edge. Peripheral ligation is provided by the phthalate groups bridging in various modes, and a chelating bpy on each Mn-III and Mn-IV ion. The cation is a rare example of a cluster with three Mn oxidation states, and it is also the first MnIV-containing phthalate complex. Fitting of variable-temperature, solid-state dc magnetic susceptibility data collected in a 0.1 T field in the 5.0-300 K range gave J(1) = J ((MnMnIV)-Mn-III) = 116(3) cm(-1), J(2) = J((MnMnIV)-Mn-II) = 6.0(4) cm(-1), J(3) = J((MnMnIII)-Mn-II) = +3.8(8) cm(-1), and g = 1.95, with TIP = 500 x 10(-6) cm(3) mol(-1). These indicate an S = 7/2 spin ground state, which was confirmed by a fit of magnetization data collected in the 0.1-7.0 T and 1.8-10.0 K ranges, and by ac in-phase susceptibility data in zero dc field and a 3.5 G ac field at a 1000 Hz frequency. (C) 2021 Elsevier Ltd. All rights reserved.