Bonding and structure in Fe(II) low-spin compounds using the Mössbauer effect

Abstract

Mössbauer centre shifts (C.S.) and quadrupole splittings (Q.S.) are presented for a wide range of six-coordinate low-spin compounds, many of which have not been prepared previously. The centre shift is an additive property of the number and type of ligands in a particular compound, and partial centre shifts (P.C.S.) values have been derived for twenty-two ligands. The P.C.S. values can be related to the bonding properties of the various ligands, and the bonding properties of the novel ligand N₂ have been examined and compared with those of CO. There is an inverse relationship between the P.C.S. values and the spectrochemical ranking of ligands. The trans:cis 2:1 quadrupole splitting ratio holds for ligands such as Cl^–, SnCl^–₃ as well as for CN^–, and the variation of Q.S. with change in neutral ligand L for trans-FeL₄Cl₂ is discussed in terms of the bonding properties of the neutral ligands.