The cooperative high-spin (⁵T₂) to or from low-spin (¹A₁) transition in dithiocyanatobis(4,7-dimethyl-1,10-phenanthroline)iron(II): Mossbauer effect and magnetism

The 57Fe Mossbauer effect and the magnetism of the ferrous compound Fe(4.7-(CH3)2-phen)2(NCS)2 have been studied in detail between 4.2 and 298K (phen=1.10-phenanthroline). At the temperature Tc=121.5K, the Mossbauer spectrum changes abruptly and the effective magnetic moment decreases. The observations are interpreted in terms of a high-spin (5T2) to or from low-spin (1A1) transition associated with a phase change at Tc. The transition is incomplete, although only a slight contribution ( approximately 2% and approximately 4% respectively) of the complementary state remains at the highest and the lowest temperature studied. Debye-Waller factors were determined from the saturation corrected areas of the Mossbauer spectra and results provide evidence for different lattice dynamical properties at the sites of 5T2 and 1A1 ground-state iron(II) molecules in the crystal.