Preparation and crystal structures of Mn II, mixed-valent Mn II/Mn III, and Mn III polymeric compounds

Abstract

The preparation and crystal structures of three polymeric Mn compounds are reported. The comproportionation reaction between Mn(OAc) 2·4H 2O and KMnO 4 in MeOH–AcOH (2:3) leads to isolation of {[Mn(OH)(OAc) 2]·AcOH·H 2O} n ( 1). The structure consists of chains of [Mn(μ-OH)(μ-OAc) 2Mn] triply-bridged units. The chains are linked into 3D networks by hydrogen-bonding interactions involving the AcOH and H 2O molecules of crystallization. Oxidation of [Mn 12O 12(O 2CPh) 16(H 2O) 4] by controlled potential electrolysis in CH 2Cl 2 with NBu n 4PF 6 as supporting electrolyte yields a brown solution which slowly turns purple and then pale yellow. Deep purple crystals, obtained by addition of hexanes, were identified crystallographically as {(NBu n 4)[Mn 2(O 2PF 2) 6]·2/3CH 2Cl 2} n ( 2), which is mixed-valent and consists of a chain of [Mn II(μ-O 2PF 2) 3Mn III] triply-bridged units. Bond distances, bond valence sum calculations, and a Jahn–Teller (JT) axial elongation at the Mn III sites confirm a trapped-valence situation. Dissolution of Mn(OAc) 2·4H 2O in EtOH results in a subsequent crystallization of a white solid analyzing as [Mn(OAc) 2·3/8H 2O] ( 3a). Crystals grown from MeOH–Et 2O were structurally identified as [Mn 4(OAc) 8(MeOH) 2] n ( 3b), and consist of Y-shaped Mn 4 units bridged by AcO − groups to give a 3D network. Variable-temperature, solid-state magnetic susceptibility studies establish that 1, 3a and 3b are antiferromagnetically coupled to give diamagnetic ground states.