Trigonal Planar Iron(II) and Cobalt(II) Complexes Containing [RS(NBu)] (R = NBu, = 2; CHPPh, = 1) as Acute Bite-Angle Chelating Ligands: Soft P Donor Proves Beneficial to Magnetic Co Species.

We prepared four new complexes, , and ,, from polyimido sulfur-centered ligands with Fe and Co amides. Their molecular structures were elucidated by single-crystal X-ray diffraction. Cobalt magnetic investigations and multiconfigurational calculations provided insight into magneto-structural correlations between the acute N,N' chelating bite angle and P-side arm donation. The deviation from an ideal trigonal planar geometry and the magnetic performance correlated in an unprecedented manor. Mononuclear cobalt species and showed slow magnetic relaxation under a small applied dc field with energy barriers of up to 33.0 and 21.9 cm, respectively. Although they possess some of the largest zero-field splitting parameters among three-coordinate cobalt single-ion magnets, both theory and experiment suggest that the high rhombicity (/) hampers large effective energy barriers to spin reversal at zero field from being obtained.