A High-Frequency EPR Study of Magnetic Anisotropy and Intermolecular Interactions on Co(II) Ions

Changing the anion in the crystal lattice induces distinct structural distortion in the [CoS4]2+ core in a family of complexes with the general molecular formula [Co(L114]X2, with L1 = thiourea (NH2CSNH2) and X = I (1), Br (2) and [Co(L1)4](SiF6) (3). The magnetic anisotropy (D) for 1-3 is quantitatively determined with the magnitude of -153(2) GHz, -168(5) GHz and < -400 GHz, respectively, by HF-EPR investigation. Besides, intermolecular exchange interactions are determined experimentally, whereby an antiferromagnetic exchange for 1 (-5.5 GHz) and 2 (-4.1 GHz) while a ferromagnetic interaction for 3 (+3.5 GHz) is witnessed (based on H = -JS1S2). The exchange interactions computed using DFT methods on a model complex of 1 disclose the presence of an antiferromagnetic exchange interaction consistent with the experimental observation. Overall, the present study provides convincing experimental evidence for the sizable influence not only of the first but also of the second coordination sphere on the magnetic anisotropy and exchange interactions in Co(II)-ions.