Unusual oxidation state distributions observed for two mixed-valence heptanuclear manganese disc-like clusters

Abstract

The synthesis, structures and magnetic properties of two new mixed-valence heptanuclear manganese clusters are described. Both complexes utilize triethanolamine (teaH3) as a bridging ligand, displaying near planar, disc-like metal topologies and are of formulae [MnII4MnIV3(tea)(teaH2)3(peolH)4](BF4)2·solv (1) and [MnII4MnIII3F3(tea)(teaH)(teaH2)2(piv)4(Hpiv)(chp)3]·0.5MeCN (2). Compound 1 is a rare mixed-valence compound containing MnII and MnIV ions only and is the first example of a heptanuclear disc with a {MnII4MnIV3} oxidation state distribution. Compound 2 is a {MnII4MnIII3} complex and displays a unique arrangement of oxidation states within the disc, when compared to other known {MnII4MnIII3} examples. Variable temperature DC and AC magnetic susceptibility studies were carried out for 1 and 2 in the 2–300 K temperature range. Compound 1 displayed an increase in the χMT susceptibility values as the temperature is decreased indicating dominant ferromagnetic interactions are present within the cluster. Fits of the χMT vs. T data reveals an S = 23/2 ground state, with several close lying excited states within 1 cm−1. Compound 2 displays an overall decrease in the χMT value as the temperature is decreased down to 2 K indicating dominant antiferromagnetic interactions present with a probable S = 4 ground state as determined from the DC and AC susceptibility data.