Mixed-valence dinuclear iron(II,III) complexes, FeIIFeIII(bpmp)(L)2] (BF4)2, have been prepared, and the structures, electrochemical properties and rates of intramolecular electron transfer of the complexes have been examined, where Hbpmp represents 2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4-methylphenol and L is 2-methoxybenzoate (omb), 3-methoxybenzoate (mmb), 4-methoxybenzoate (pmb), 3,5-dimethoxybenzoate (dmb), 3,4,5-trimethoxybenzoate (tmb) or 4-biphenylcarboxylate (bpc). It turns out from the Móssbauer spectra that the valence states of iron atoms of [FeIIFeIII(bpmp)(omb)2] (BF4)2, [FeIIFeIII(bpmp)(pmb)2] (BF4)2, [FeIIFeIII(bpmp)(tmb)2] (BF4)2 and [FeIIFeIII(bpmp)(bpc)2] (ClO4)2 are localized at 78 K and delocalized at 293 K. The temperature dependence of the spectra is interpreted by assuming intramolecular electron transfer between two energetically equivalent vibronic states FeAIIFeBIII and FeAIIFeBIII. The Mössbauer spectra of [FeIIFeIII(bpmp)(dmb)2] (BF4)2 show the superposition of the relaxation spectrum between iron(II) and iron(III), and of the spectrum of the average valence states at 293 K; the average valence states are partly observed even at 78 K. The valence states of [FeIIFeIII(bpmp)(mmb)2] (BF4)2 are localized over the temperature range from 78 K to 293 K. The single-crystal X-ray structure of [FeIIFeIII(bpmp)(bpc)2] (ClO4)2 was determined at 293 K. The complex crystallizes in the orthorhombic space group Fdd2, which has a unit cell of a = 27.056(1) Å, b = 42.652(0) Å, c = 12.151(0) Å and Z = 8. A refinement was performed with 2340 unique reflections [I > 3σ(I)] to give R = 0.085, Rw = 0.099. The two iron atoms are located symmetrically to a C2 axis, which presents in the molecule, and are crystallographically equivalent. The mean Fe-O length is intermediate between the FeII-O and FeIII-O values, indicating that both iron atoms are in an averaged valence state.
All Science Journal Classification (ASJC) codes