Spectroscopic and magnetic studies of erbium(III)-TEMPO complex as a potential single-molecule magnet: Interplay of the crystal-field and exchange coupling effects

Crystallographic, spectroscopic, and magnetic studies of three-center systems: lanthanoid-Ln(3+) ions doubly-coordinated by TEMPO (2,2,6,6-tetramethylpiperidin-1-oxyl) radicals [Ln-TEMPO2] are reported. The temperature dependence of alternating-current magnetic susceptibility indicates the single-molecule-magnet behavior of Er-TEMPO2, exhibiting relatively slow magnetization relaxation. Well-resolved absorption spectra were obtained only for Er-TEMPO2. Other samples yielded spectra not amenable for meaningful interpretation. The crystal-field parameters (CFPs) determined from the measured Er3+-energy levels served as starting CFPs for fitting the direct-current magnetic susceptibility result. Compatibility of the so-determined and fine-tuned CFPs, and interplay between crystal-field related effects and exchange-coupling effects are considered. Exchange couplings in Ln-TEMPO2 appear antiferromagnetic and unexpectedly large. (C) 2016 Elsevier B.V. All rights reserved.