Magnetic properties of cobalt(II) complexes. Part III. Crystal magnetic anisotropy of α-dichlorobis(pyridine)cobalt(II)

The principal and mean magnetic susceptibilities of Co(py)2Cl2(py = pyridine) have been measured in the temperature range 300–80 K. They are characterized by an interesting anomaly at ca. 150 K when the crystal anisotropy in the ab plane abruptly changes sign. There is an associated transition in the anisotropy in the bc plane but none is observed for mean moments. The overall effect on principal molecular magnetic moments appears sufficiently small, however, not to interfere with the theoretical interpretation of the magnetism of Co(py)2Cl2 within the framework of a tetragonally squashed octahedron. The mean moment of Co(py)2Cl2 at room temperature is well known to be high compared with other ‘octahedral’ cobalt(II) ions and a discussion of this phenomenon in terms of the sense of tetragonality is presented as are some general comparisons with the preceding paper.