The sign of the 57Fe quadrupole splittings in iron(II) low-spin compounds: partial quadrupole splittings and bonding properties of ligands

Abstract

The signs of V_zz(and e²qQ) at the ⁵⁷Fe nucleus for the following compounds have been measured by use of the Mössbauer magnetic field technique: trans-FeCl₂(p-MeO·C₆H₄·NC)₄, trans-FeCl₂(depe)₂[depe = 1,2-bis(diethylphosphino)ethane]. Na₃[Fe(CN)₅NH₃],H₂O, K₃[Fe(CN)₅H₂O],7H₂O, all positive; cis-FeCl₂(p-MeO·C₆H₄·NC)₄ and trans-Fe(CN)₂(EtNC)₄, both negative. The 2: –1 trans:cis ratio has been confirmed, and partial quadrupole splittings (p.q.s.) for sixteen ligands have been assigned. These p.q.s. values become more positive as the π-acceptor function of a ligand increase, and the σ-donor properties of a ligand decreases [i.e. p.q.s.α(π—σ)]. The p.q.s. values are related to the bonding properties of these ligands.