High-field magnetization and high-frequency ESR study on the tetranuclear cluster composed of π-electrons (S= 1/2 ) and d-electrons (S=5/2)

Recently, Iwamura's group has succeeded in synthesizing the interesting new tetranuclear cluster composed of two paramagnetic Mn²⁺ ions (S=5/2 per ion) and two organic free radicals (S= 1/2 per radical) as bridging ligand, [{Mn(hfac)₂}₂(bnn)] (bnn=2,2′-bis[(1-oxyl-3-oxide-4,4,5,5-tetramethyl- imidazolinyl)]). The crystal structure is triclinic (space group P1) and each cluster is composed of two triangles which share their own base like a 'butterfly'. There are two kind of exchange pathways within the cluster and both of them are likely to be antiferromagnetic. Therefore, spin frustration may occur and we expect many possible ground states with different total spins (S_T=0 to S_T=6), depending on the relevant interactions and magnetic field. We wish to discuss the important magnetic parameters such as exchange interactions and anisotropy which characterize this interesting system through measurements of high-field magnetization and high-frequency electron spin resonance.