Effects of temperature and pressure on the Mossbauer spectra of models for the [4Fe-4S]2+ clusters of iron-sulfur proteins and the structure of [PPh4]2[Fe4S4(SCH2 CO2C2H5)4]

Changes in the Mossbauer spectra of [Cat](2)[Fe4S4((SBu)-Bu-t)(4)] salts where Cat = N(alkyl)(4) and PPh4 are apparent when these compounds are subjected to temperature changes in the range 78-298 K or to pressures up to 6.28 Cpa. The Mossbauer data are discussed in terms of the temperature and pressure dependence. It is revealed for the [4Fe-4S](2+) clusters that the iron atoms become less electronically symmetric as the temperature is lowered or pressure is increased. The crystal structure of [PPh4](2)[Fe4S4(SCH2CO2C2H5)(4)] is reported and discussed in relation to the effect of pressure on the Mossbauer spectroscopic data. It is possible to arrange the compounds into three classes depending on their response to the application of pressure.