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

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 Mossbauer 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 D4h symmetry are observed.