Preparation and crystal structures of MnII, mixed-valent MnII/MnIII, and MnIII polymeric compounds

Abstract

The preparation and crystal structures of three polymeric Mn compounds are reported. The comproportionation reaction between Mn(OAc)2·4H2O and KMnO4 in MeOH-AcOH (2:3) leads to isolation of {[Mn(OH)(OAc)2]·AcOH·H2O}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 H2O molecules of crystallization. Oxidation of [Mn12O12(O2CPh)16 (H2O)4] by controlled potential electrolysis in CH2Cl2 with NBu2nPF6 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 {(NBu4n])[Mn2(O2 PF2)6]·2/3CH2 Cl2}n (2), which is mixed-valent and consists of a chain of [MnII(μ-O2PF2)3 MnIII] triply-bridged units. Bond distances, bond valence sum calculations, and a Jahn-Teller (JT) axial elongation at the MnIII sites confirm a trapped-valence situation. Dissolution of Mn(OAc)2·4H2O in EtOH results in a subsequent crystallization of a white solid analyzing as [Mn(OAc)2·3/8H2O] (3a). Crystals grown from MeOH-Et2O were structurally identified as [Mn4(OAc)8(MeOH)2]n (3b), and consist of Y-shaped Mn4 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. © 2002 Elsevier Science Ltd. All rights reserved.