Importance of the anisotropic exchange interaction for the magnetic anisotropy of polymetallic systems

A prerequisite to understand and subsequently to allow applications of the magnetic properties of polymetallic exchange coupled systems is a detailed insight into the magnetic properties of their elementary building blocks and the interaction between them. Such an understanding passes through the quantification of the relative contributions of single-ion and exchange terms to the overall magnetic properties of the system. In the general case, the quantification of these two kinds of contributions is possible when numerous spin-states are experimentally observed since single-ion and exchange terms project differently on the ground and various excited spin-states of an exchange coupled system. We present here highly resolved multifrequency (X-, K-, and Q-band) CW-EPR spectra obtained on a heterooctametallic ring [Me2NH2][Cr(III)(7)Cd(II)F-8((CH3)(3)CCOO)(16)] (1). The spectra of 1 provide a rare example of a polymetallic system where detailed information on the spin-Hamiltonian parameters of excited spin-states is experimentally observed. Analysis of these spectra allowed the direct quantification of the contributions of single-ion and exchange anisotropy terms to the magnetic properties of the system.