From Positive to Negative Zero-Field Splitting in a Series of Strongly Magnetically Anisotropic Mononuclear Metal Complexes.

A series of mononuclear [M(hfa)(pic)] (Hhfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione; pic = 4-methylpyridine; M = Fe, Co, Ni, Zn) compounds were obtained and characterized. The structures of the complexes have been resolved by single-crystal X-ray diffraction, indicating that, apart from the zinc derivative, the complexes are in a trans configuration. Moreover, a dramatic lenghthening of the Fe-N distances was observed, whereas the nickel(II) complex is almost perfectly octahedral.

Determination of zero-field splitting in Co halide complexes with magnetic and far-IR measurements.

Three penta-coordinate Co complexes with halide substitutes were synthesized. Their zero-field splitting (ZFS) parameters were determined by fitting dc magnetic data and far-infrared magneto-transmission spectra. The results gave an unusual case that complexes with heavier halide atoms bear smaller ZFS parameters.