Magneto-Structural Correlations in Pseudotetrahedral Forms of the [Co(SPh)4]2– Complex Probed by Magnetometry, MCD Spectroscopy, Advanced EPR Techniques, and ab Initio Electronic Structure Calculations

The magnetic properties of pseudotetrahedral Co(II) complexes spawned intense interest after (PPh4)2[Co(SPh)4] was shown to be the first mononuclear transition-metal complex displaying slow relaxation of the magnetization in the absence of a direct current magnetic field. However, there are differing reports on its fundamental magnetic spin Hamiltonian (SH) parameters, which arise from inherent experimental challenges in detecting large zero-field splittings. There are also remarkable changes in the SH parameters of [Co(SPh)4]2– upon structural variations, depending on the counterion and crystallization conditions. In this work, four complementary experimental techniques are utilized to unambiguously determine the SH parameters for two different salts of [Co(SPh)4]2–: (PPh4)2[Co(SPh)4] (1) and (NEt4)2[Co(SPh)4] (2). The characterization methods employed include multifield SQUID magnetometry, high-field/high-frequency electron paramagnetic resonance (HF-EPR), variable-field variable-temperature magnetic ci...