Unusual Mn5 cluster with a ‘twisted bow-tie’ topology and MnIIMnIII2MnIV2 oxidation states: Synthesis, structure, and magnetic properties

Abstract

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 (phthH2) and 2,2′-bipyridine (bpy), respectively. The MnO4-:phthH2:bpy = 1:2:1 reaction in MeOH has led to isolation of [Mn5O4(phth)3(phthH)(bpy)4](phthH2)(phthH) (1), whose Mn5 cation possesses a ‘twisted bow-tie’ topology comprising two near-perpendicular MnII,III,IV3 scalene triangles fused at the MnII ion. Each triangle is bridged by a central μ3-O2- and a μ2-O2- on the MnIIIMnIV edge. Peripheral ligation is provided by the phthalate groups bridging in various modes, and a chelating bpy on each MnIII and MnIV 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 J1 = J(MnIIIMnIV) = − 116(3) cm−1, J2 = J(MnIIMnIV) = − 6.0(4) cm−1, J3 = J(MnIIMnIII) = +3.8(8) cm−1, and g = 1.95, with TIP = 500 × 10-6 cm3 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.