Effect of Pressure on the Electronic Structure of Complexes of Ferrous Iron with Substituted Phenanthrolines

The effect of pressure to 180 kbar has been studied on the spin state of ferrous iron in complexes and with substituted phenanthrolines. The tris complexes are low spin at 1 atm and partially convert to high spin at high pressure. The bis complexes with isothiocyanate and chloride are high spin at 1 atm. With increasing pressure they convert partially to low spin. At sufficiently high pressure the conversion tends to level and, in some cases, a reverse trend sets in. At a given pressure the amount of low spin present correlates very well with the low spin isomer shift, which, in turn, can be related to the electronic structure of the ligand and the size of the ligand field Δ. A correlation between conversion and low spin quadrupole splitting indicates that local distortion is also a factor in the change of spin state. Three compounds were studied where steric effects are prominent. The effect of pressure on their spin state is discussed in some detail.