A SINGLE-CRYSTAL ESEEM STUDY OF FE(CN)(6)(3-) DOPED INTO K3CO(CN)(6) - INDICATIONS FOR A STRUCTURAL PHASE-TRANSITION

An ESEEM study has been performed on Fe(CN)(6)(3-) doped into K3Co(CN) (6). The experimental facts indicate that a phase transition occurs be tween 10 and 65 K. Analysis of the ESEEM spectra measured at 7 K leads to the conclusion that the Fe(CN)(6)(3-) ion has lost its inversion c entre below the phase-transition temperature. From the angular depende nce of the ESEEM lines it was inferred that, compared with the structu re at room temperature, the M(CN)(6)(3-) (M = Fe3+ Co3+) unit at low t emperature is rotated by an angle of 54.7 degrees around the c axis of the crystal. After this rotation the major principal axes of the hype rfine matrices and quadrupole tensors coincide with the iron-cyanide b onds. This is in agreement with what could be expected on the basis of earlier ENDOR studies of the same complex in other hosts.