Paramagnetic anisotropy and electron spin resonance data on the planar S = & bis(dithioacetylacetonato)cobalt(II) are discussed and interpreted assuming the unpaired electron lies in the dz2 orbital. Recently there has been much interest in the magnetic and electronic properties of "square" planar cobalt(II) compounds [ 11. Bis(dithioacetylacetonato)cobalt(II) (abbreviated here to Co(SacSac)2) provides one of the rare examples where the cobalt(H) atom is bonded to four sulphur atoms in a planar configuration [2,3], and is paralleled [4] only by bis(maleonitriledithiolato)co-b&III) (abbreviated here to Co(mT)z)_ The magnetic properties of Co(SacSac)2 would, therefore, be expected to be similar to Co(MNT)2 with a characteristically large in-plane anisotropy [4]. However, recent interpretations [5] of NMR contact shift data on Co(SacSac)2 have assumed that its magnetic properties are very different from those of Co(MNT)2 but are similar to those of (Ycobalt@) phthalocyanine (abbreviated here to LY-CoPc) which has isotropic in-plane magnetic behaviour [6]. This assumption is at variance with our paramagnetic anisotropy and electron spin resonance studies on Co(SacSac)2, which establish that the magnetic properties of Co(SacSac)2 and CO(MNT)~ are very closely related. Single crystals of Co(SacSac)s belong to the orthorhombic system with two inequivalent molecules in the unit cell. The molecule is almost perfectly planar [3] and is shown diagramatically in fig. 1. The corresponding nickel(I1) compound, Ni(SacSac)2, is isostructural with Co(SacSac)2 [3].
The magnetic anisotropy and average susceptibility were measured between room temperature and about 9O0K by the methods described elsewhere ['7], and the principal molecular moments were calculated from the X-ray data. ESR measurements were made at 77OK on the Co(SacSac)2 doped in the diamagnetic Ni(SacSac)2 using a Varian-X-band spectrometer.
Our data are summarized In table 1. and are compared with the results of previous magnetic studies on CY-CoPc