Adducts of hexacyanoferric(II) acid, trans-dicyanotetrakis(methyl isocyanide)iron(II), and trans-dicyanotetrakis(ethyl isocyanide)iron(II) with boron trihalides. Infrared and Mössbauer spectroscopic studies

Abstract

Hexacyanoferric(II) acid readily absorbs boron trifluoride (but not boron trichloride) to form the adduct Fe(CNH)₄(CN)₂,2BF₃. The trans-dicyanotetrakis(alkyl isocyanide)iron(II) complexes Fe(CNMe)₄(CN)₂ and Fe(CNEt)₄(CN)₂ readily absorb either of these boron trihalides to form adducts Fe(CNR)₄(CN)₂,2BX₃. The i.r. and Mössbauer spectra of these adducts are interpreted in terms of structures Fe(CNR)₄(CN,BX₃)₂ with the Lewis acids linked to the nitrogen atoms of the cyanide group. The spectra are consistent with local octahedral symmetry at iron, indicating the similar π-acid ligand properties of the groups CNR and CNBX₃, although in the cyanide stretching region the two i.r. bands appropriate for D_4h symmetry are observed.