Long-range exchange interactions and integer-spin S(t) = 2 EPR spectra of a Cr(III)Zn(II)Cr(III) species with multiplet mixing.

Synthesis, structural, and spectroscopic characterization of the linear cationic complex [LCrIII{μ-[dmg)3ZnII}CrIIIL]2+ (1) in which L = 1,4,7-trimethyl-1,4,7-triazacyclononane and dmg is the dimethylglyoximato anion are reported. The Cr···Cr distance of 1 is 7 A. SQUID magnetic susceptibility measurements reveal the presence of long-range exchange interaction of the CrIII terminal ions, mediated by the diamagnetic ZnII(dmg)3 “bridging ligand” (J0 = −4.4 cm-1, ℋex = −2J0S1S2, Si = 3/2). Multifrequency EPR measurements (S-, X-, Q-band) on frozen solutions were used to establish the intramolecular nature of the exchange coupling and to determine the zero-field splitting (ZFS) parameters and the anisotropic contributions of spin coupling. An effective spin Hamiltonian description was applied for interpretation of the spectra originating from the St = 2 total spin manifold which included up to fourth-order terms for the ZFS. By the help of alternative simulations with the full coupling matrix for two spins Si...