Moessbauer study on K/sub 2/Fe/sub 2/(CO)/sub 8/ in an external magnetic field

We consider in more detail what changes occur in the Moessbauer parameters when apical and equatorial CO groups are replaced by Fe(CO)/sub 4//sup =/ in the trigonal bipyramidal Fe(CO)/sub 5/ molecule. We use Bancroft's concept of the partial contributions to the quadrupole splitting (QS). The main difference between the HFS parameters for the Moessbauer spectra for the possible structures will be a marked difference in the asymmetry parameters. Here /eta/ can be determined for 1/2 /yields/ 3/2 transitions if there is combined hyperfine magnetic and quadrupole interaction. In a diamagnetic (K/sub 2/Fe/sub 2/(CO)/sub 8/), such combined interaction can occur only from the use of external magnetic fields. The Moessbauer spectra were recorded in an Oxford Instruments cryostat having a superconducting solenoid at 4.2 K without a field or with a longitudinal field of 4.6 T. The spectra show that the EFG tensor for K/sub 2/Fe/sub 2/(CO)/sub 8/ is axially symmetric (/eta/ 0) and that the sign of QS is positive.