Muon spin rotation and Mossbauer investigations of the spin transition in [Fe(ptz)(6)](ClO4)(2)

The compound [Fe(ptz)(6)],(ClO4)(2) (Ptz = 1-propyl-tetrazole) displays a gradual thermal spin crossover with magnetic susceptibility in easurements (similar to4.2-300 K) showing that the transition is centered around T-12 similar to 150 K and extends from similar to90-190 K. Evidence of the scope to track a thermally induced spin transition using muon spin rotation (muSR) is provided in particular via the temperature dependence of the initial asymmetry parameter in the zero field as well as the relaxation rates. The spectral line broadening observed in the Mossbauer spectra of [Fe(Ptz)(6)](ClO4)(2) at similar to200 K is attributed to relaxation phenomena associated with the dynamics of the crystal lattice. Dynamic processes are also detected by muSR as revealed by the pronounced increase of the relaxation rate of a fast-relaxing component above 200 K. Muonium-substituted radicals delocalized on the tetrazole ring have been identified on the basis of applied magnetic field muSR experiments from 10 to 2000 Oe.