A synthetic iron-containing prismane complex: Peculiar electron-delocalization and spin-coupling properties deduced from mössbauer and magnetization studies

The prismane complex (Et₄N)₃[Fe₆S₆Cl₆] was investigated by Mössbauer spectroscopy under various experimental conditions, i.e. at temperatures 0.3-250 K in a field of 20 mT (⊥γ), at 300, 600 and 900 mK in a field of 1 T (⊥γ), and at 4.2 and 100 K in a field of 6.1 T (∥γ). The obtained temperature dependences of the quadrupole splitting, asymmetry parameter and line shape are described successfully in terms of electron tunneling below and electron hopping above 10 K. The temperature variation of the magnetic hyperfine splitting is analyzed in terms of the stochastic theory of relaxation with two contributions, i.e. spin relaxation among the substates of the S_tot = 1/2 Kramers system and pairwise spin flips within the prismane cluster keeping the orientation of the total cluster spin preserved. Magnetization measurements in the temperature range 2-295 K are analyzed with a spin-Hamiltonian which includes explicitly superexchange and double exchange contributions. Both the analysis of the Mössbauer measurements and the analysis of the magnetization measurements reveal peculiar electron-delocalization and spin-coupling properties of the prismane cluster, i.e. three 'excess' electrons are delocalized over three metal pairs and the spin of the three metal pairs couples to the total cluster spin S_tot = 1/2.