High-field EPR study of a ReCl$_{4}$(CN)$_{2}$ molecular magnet building block

Slow magnetic relaxation has been observed in the single-chain magnet (DMF)$_{4}$MReCl$_{4}$(CN)$_{2}$ (M = Mn, Fe, Co, Ni) [D. Harris \textit{et al}., J. Am. Chem. Soc. \textbf{132}, 3980 (2010)]. The ReCl$_{4}$(CN)$_{2}$ \textbf{(1)} molecule has been synthesized in which the local environment of the Re$^{IV}$ ion is same as in the single-chain magnet. Electron Paramagnetic Resonance (EPR) measurements have been performed on single crystal of complex \textbf{1} to determine the magnetic anisotropy of the Re$^{IV}$ ions. Both intra and inter Kramer's doublet transitions are observed in high-field (up to 36T) EPR experiments. The data indicate a significant axial anisotropy of the easy-plane type ($D>$ 0), with sizeable rhombic $E$ term. In light of these findings, we are developing a theoretical model to account for the slow relaxation in the single-chain magnet.