Structural, magnetic, and spectroscopic studies of tetrakis(pyridine) complexes of iron(II) sulfonates

Abstract

The iron(II) complexes Fe(NC5H5)4(RSO3)2 where R = CF3, CH3, and p-CH3C6H4 have been prepared and their crystal structures determined by single crystal X-ray diffraction. Crystals of trans-bis(methanesulfonato-O)tetrakis(pyridine)iron(II) are monoclinic, a = 16.524(2), b = 9.1127(6), c = 18.684(2) Å, β = 109.903(6)°, Z = 4, space group Pn. The structure was solved by conventional heavy-atom methods and was refined by full-matrix least-squares procedures to R = 0.034 and Rw = 0.038 for 4243 reflections with I ≥ 3α(I). Crystals of trans-bis(trifluoromethanesulfonato-O)tetrakis(pyridine)iron(II) are monoclinic, a = 10.456(1), b = 9.2981(8), c = 14.625(2) Å, β = 96.372(6)°, Z = 2, space group Pn. Structure solved and refined as above to R = 0.036, and Rw = 0.037 for 1483 reflections with I ≥ 3σ(I). Crystals of trans-bis(p-toluenesulfonato-O)tetrakis(pyridine)iron(II)are orthorhombic, a = 40.818(2), b = 9.8722(6), c = 17.3544(7) Å, Z = 8, space group Fdd2. The structure was solved by Patterson and Fourier syntheses and was refined by full-matrix least-squares procedures to R = 0.030 and Rw = 0.032 for 1851 reflections with I ≥ 3σ(I). All three structures show discrete octahedral molecules with monodentate trans-coordinated sulfonate groups. Two crystallographically independent molecules are observed in the R = CH3 structure, the difference between them involving the orientation of the CH3SO3 groups with respect to the O—Fe—O vector. The FeN4O2 chromophore in each compound is a tetragonally compressed octahedron (approximate D4h, symmetry) with average Fe—N distances of 2.21, 2.23, and 2.24 Å and Fe—O distances of 2.11, 2.06, and 2.08 Å for theCF3, CH3, and p-CH3C6H4 derivatives, respectively. The compounds were studied using vibrational, electronic, and Mössbauer spectroscopic methods, magnetic susceptibility measurements, and differential scanning calorimetry. Quadrupole splitting values from Mössbauer spectra indicate a 5B2g ground state for all three compounds and magnetic susceptibility data (310–4.2 K) have been analyzed assuming this ground state, using both a crystal field and a zero-field splitting model.