COEXISTENCE OF ANISOTROPIC AND MOTIONALLY AVERAGED EPR-SPECTRA IN A JAHN-TELLER SYSTEM - CU2+ ION IN [FE(NH(2)TRZ)(3)(NO3)(2) COMPOUND

Electron spin resonance in copper-doped polymeric iron(II)-1,2,4-triaz ole compound [Fe(NH(2)trz](3)(NO3)(2) is studied at different temperat ures below the low spin to high spin transition of Fe2+ ions. Between liquid helium and liquid nitrogen temperatures typical anisotropic spe ctra of Cu2+ in a static Jahn-Teller configuration are observed, while the room temperature spectra undergo dynamic averaging. At intermedia te temperatures both the anisotropic and averaged spectra coexist. The se results are accounted for assuming a Gaussian distribution of the e nergy difference Delta between the lowest and the higher valleys of th e Jahn-Teller potential energy surfaces, with the mean Delta-value ca. 0.021 eV and the standard deviation ca. 0.0066 eV. (C) 1998 Elsevier Science Ltd. All rights reserved.