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 [Mn^II₄Mn^IV₃(tea)(teaH₂)₃(peolH)₄](BF₄)₂·solv (1) and [Mn^II₄Mn^III₃F₃(tea)(teaH)(teaH₂)₂(piv)₄(Hpiv)(chp)₃]·0.5MeCN (2). Compound 1 is a rare mixed-valence compound containing Mn^II and Mn^IV ions only and is the first example of a heptanuclear disc with a {Mn^II₄Mn^IV₃} oxidation state distribution. Compound 2 is a {Mn^II₄Mn^III₃} complex and displays a unique arrangement of oxidation states within the disc, when compared to other known {Mn^II₄Mn^III₃} 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 χ_MT susceptibility values as the temperature is decreased indicating dominant ferromagnetic interactions are present within the cluster. Fits of the χ_MT 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 χ_MT 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.