Abstract :
The influence of the magnetic interaction between a paramagnetic metal ion and a radical ligand upon the spectroscopic (UV-vis and/or NMR) properties will be described and discussed mainly for the mixed ligand complexes, M(L)(X) (M = Ni(II), Cr(III); L = nitroxide radicals such as NIT2py (2-(2-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-3-oxide-1-oxyl) or IM2py (2-(2-(pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxy), X = ?-diketonates). For the Ni(II) and Cr(III) complexes, the spin-forbidden d–d bands demonstrated some intensity enhancement and the charge transfer band from the d orbital to the SOMO ?* newly appeared in the visible region. Their variable temperature UV-vis spectra substantiated the antiferromagnetic and ferromagnetic interactions as revealed by the magnetic susceptibility measurements. The spectroscopic behaviors with variation of the ?-diketonates is examined in connection with magnetic interaction constant J values, exhibiting the coligand effect, e.g., in terms of the exchange mechanism. For the Mn(II), Co(II), Ni(II), and Ln(III) complexes with the NIT2py and/or IM2py or their derivatives and for the Cr(III) and diamagnetic Co(III) complexes with monodentate NIT3or 4py and IM3- or 4py, the spectroscopic properties are also found to be influenced to the d orbitals from the coordinated nitroxides.
