CRAMPING A MOLECULAR ROLLERBALL - INVESTIGATION OF THE EFFECT OF PRESSURE ON THE MOSSBAUER-SPECTRA OF 3 CYCLOPENTADIENYL(ARENE)IRON(II) SALTS

The effect of pressure on the Mossbauer spectra of salts of [CpFePhH]( +), [CpFePhF](+), and [CpFePhMe](+) has been examined over the range o f 10(-4) Cpa to about 4 GPa. Dynamic reorientation of salts of the fir st two cations may be arrested on the Mossbauer time scale by the appl ication of pressure (0.85 and 1.36 GPa). For these two cations, extrap olated quadrupole splitting values were obtained at 10(-4) GPa at room temperature that help to verify and extend previous models of motion. A simplified theoretical model of the reorientation of the [CpFePhH]( +) cation is presented. It is also shown that at pressures above those which arrest motion, the compounds manifest a gradual decrease of qua drupole splitting with increasing pressure. An explanation is discusse d.