Variable temperature EPR, optical and magnetic studies of a macrobicyclic cage complex of Cu(II) in pure and zinc-doped systems: evidence for a Jahn-Teller distortion

Abstract

Single-crystal EPR spectra of a cage complex of copper(II), [Cu{(NH₃)₂sar}](NO₃)₄. H₂O and Cu²⁺-doped[Zn{(NH₃)₂sar}](NO3)4 . H₂O have been recorded as a function of the orientation of the magnetic field in all three crystallographic planes at 300K and 77K and as a function of temperature down to 22K, in order to observe static and dynamic Jahn-Teller effects at lower and higher temperatures, respectively. Crystal g tensor values were obtained by least-squares fitting method and by introducing the Schonland procedure. Finally the local g values were calculated from exchange-averaged g values. Optical spectra were recorded at 12K and 298K to evaluate the Jahn-Teller stabilization energy. Variable temperature infrared spectra down to cryogenic temperatures were recorded to observe any change in Cu—N stretching frequency of this complex. Polycrystalline magnetic susceptibility measurements were made over a wide range of temperature (5-290K) to determine the nature and extent of exchange interactions present in this system.