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

The synthesis, structures and magnetic properties of two new mixed-valence heptanuclear manganese clusters are described. Both complexes utilize triethanolamine (teaH(3)) as a bridging ligand, displaying near planar, disc-like metal topologies and are of formulae [(Mn4Mn3IV)-Mn-II(tea)(teaH(2))(3)(peolH)(4)](BF4)(2).solv (1) and [(Mn4Mn3F3)-Mn-II-F-III(tea)(teaH)(teaH(2))(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 (Mn4Mn3IV)-Mn-II oxidation state distribution. Compound 2 is a (Mn4Mn3III)-Mn-II complex and displays a unique arrangement of oxidation states within the disc, when compared to other known (Mn4Mn3III)-Mn-II 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 chi T-M susceptibility values as the temperature is decreased indicating dominant ferromagnetic interactions are present within the cluster. Fits of the chi T-M 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 chi T-M 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.