Valence states and structure of mixed-valence dinuclear iron(II,III) complexes [Fe_2(2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4-methyl-phenol)(L)_2(BF_4)_2

摘要

Mixed-valence dinuclear iron(II,III) complexes,[e~(II)Fe~(III)(bpmp) (L)_2](BF_4)_2,have been prepared,and the strucures,electrochemical properties and rates of intramlecular electron ransfer of the complexes have been examined,where Hbpmp represents 2,6-bis[bis(2-pyridyylmethyl)aminomethyl]-4-methylphenol and L is 2-methoxybenzoate (omb),3-methoxybenzoate (mmb),4-methoxybenzoate (pmb),3,5-dimehtoxybenzoate (dmb),3,4,5-trimethoxybenzoate [Fe~(II)Fe~(III)(bpmp)(omb)_2] (BF_4)_2,[Fe~(II)Fe~(III)(bpmp)(pmb)_2] (BF_4)_2),[Fe~(II)Fe~(III)(bpmp)(tmb)_2]-(ClO_4)_2 are localized at 78K and delocalized at 293K.The temperature dependence of the spectra is interpreted by assuming intramolecular electrontransfer between two energetically equivalent vibronic states Fe_A~(II)Fe_B~(II).The Mossbauer spectra of [Fe~(II)Fe~(III)(bpmp) (dmb)_2](BF_4)_2 show the superposition of the relaxation spectrum between iron (II) and iron(III),and of the spectrum of the average valence states at 293K;theaverage valence states are partly observed even at 78K.The valence states of [Fe~(IIFe~(III)(bmpm) (mmb)_2](BF_4)_2 are localized over the temperature range from 78 K to 293 K.The single-crystla X-ray structure of [Fe~(II)Fe~(III)(bpmp) (bpc)_2](ClO_4)_2 was determined at 293K.The complex crystallizes in the orthorhombic space group Fdd2,which has a unit cell of a=27.056(1) A,b=42.652(0)A,c=12.151(0) A and Z=8.A refinement was performed with 2340 unique reflections [I>3delta(I)] to give R=0.085,R_w=0.099.The two iron atoms are located symmetrically to a C_2 axis,which presents in the molecule,and are crystallographically equivalent.The mean Fe-O length is intermediate between the Fe~(II)-O and Fe~(III)-O values,indicating that both iron atoms are in an averaged valence state.