Volume contraction calculations, high pressure

Since it can be predicted that depopulation of the (high-spin) sextet level in favour of the (low-spin) doublet level should be accompanied by a contraction of the [FeS6] core in spin transition systems, it is to be expected that the position of the spin equilibrium K will depend on pressure. This has been experimentally verified for several tris(dithiocarbamato)iron(III) complexes ita chloroform solution at pressures up to 5000 atmospheres at room temperature. On the assumption that the molecular volume contraction AV arises entirely as a result of the spin change, equation (15) can be applied to the calculation of the volume change. Values of A V of the order of 5 cm3 mol-1 were obtained for systems with a wide variety of N substituents.289,290 The values correspond to a contraction of the Fe—S bond length of about 0.1 A, during the 5 A - 2T transition. 

---