Solvate molecule effects and unusual Fe-57 Mossbauer line broadening in the valence detrapping of mixed-valence [Fe3O(O2CCH3)(6)(3-Et-py)(3)]center dot S

A new series of mixed-valence mu(3)-oxo-bridged Fe3O complexes with the composition [Fe3O(O2CCH3)(6)(3-Et-py)(3)]. S, where 3-Et-py is 3-ethylpyridine and the solvate molecule S is either 0.5C(6)H(5)CH(3) (1), 0.5C(6)H(6) (2), CH3CN (3), or CH3CCl3 (4), is reported. The complex [Fe3O(O2CCH3)(6)(3-Et-py)(3)]. 0.5C(6)H(5)CH(3) (1) crystallizes in the orthorhombic space group Fdd2 which at 298 K has a unit cell with a = 22.726(8) Angstrom, b = 35.643(14) Angstrom, c = 20.816(6) Angstrom, and Z = 16, Refinement with 5720 observed [F > 5 sigma(F-0)] reflections gave R = 0.0337 and R(w) = 0.0390. An analysis of the bond lengths in complex 1 shows that it is the most valence-trapped Fe3O complex reported at room temperature. The complex [Fe3O(O2CCH3)(6)(3-Et-py)(3)]. CH3CCl3 (4) crystallizes in the triclinic space group <P(1)over bar> which at 238 K has a unit cell with a = 12.764(2) Angstrom, b = 13.1472(2) Angstrom, c = 15.896(3) Angstrom, alpha = 78.01(2)degrees, beta = 89.38(2)degrees, gamma = 61.38(1)degrees, and Z = 2. Refinement with 6264 observed [F > 5 sigma(F-0)] reflections gave R = 0.0435 and R(w) = 0.0583. In this mu(3)-oxo-bridged complex all three iron ions are inequivalent. Powder X-ray diffraction patterns taken at room temperature show that complexes 1 and 2 are isostructural and that complexes 3 and 4 are isostructural, Variable-temperature Fe-57 Mossbauer spectra were collected for all four complexes. The data for complexes 1 and 2 clearly indicate that these two complexes are totally valence trapped. On the other hand, Mossbauer spectra (43-293 K) for complexes 3 and 4 show that these two complexes become valence detrapped at temperatures near room temperature, Two doublets are seen at low temperature and they move together to become a single doublet at similar to 293 K. Examination of the line width versus temperature for each of the two components of the two doublets points to a curiosity. The two components of the ''Fe-III'' doublet and the lower-velocity component of the ''Fe-II'' doublet do not exhibit any line broadening, whereas the higher velocity ''Fe-II'' component shows a surge in line width in the similar to 70-150 K range. Possible explanations for these unusual line width responses are discussed.