Synthesis and Magnetism of Co2III$_{2}^{III}$Co5II$_{5}^{II}$ and Co2III$_{2}^{III}$Co6II$_{6}^{II}$ Complexes, and the Role of the Free Choice of Local Coordinate Frames for Interpreting Magnetic Parameters

Two new polynuclear high-spin Co$^{II}$ coordination clusters have been synthesised using the proligand N-allyldiethanolamine (2,2′-(allylazanediyl)bis(ethan-1-ol), adeaH$_2$ ). The heptanuclear coordination cluster [Co$^{III}_2$Co$^{II}_5$ (adea)$_2$(μ$_3$ -OH)$_2$ (μ$_3$ -OMe)$_2$ (μ$_2$ OMe)$_2$ (piv)$_6$(MeOH)$_2$]⋅2MeOH (1) possesses a disk-like core motif and was used as a starting material for the syntheses of the octanuclear coordination cluster [Co$^{III}_2$ Co$^{II}_6$(adea)$_2$(μ$_3$-OH)$_4$(piv)$_{10}$]⋅2Hpiv⋅2MeCN (2). From magnetic measurements a magnetic model could be developed which fits the χT versus T and M versus B curves accurately. In order to rationalise the magnetic properties of 2 it was found essential to consider the consequences of the freedom to choose the local coordinate frames used for describing the individual Co$^{II}$ centres in the cluster. The far-reaching implications of this for the interpretation of magnetic parameters derived from magnetic modelling of clusters containing highly-anisotropic metal ions are discussed.