“…22,31 It should be stressed that the tetrahedral S = 3/2 (PPh 4 ) 2 [Co(SPh) 4 ] complex 32,33 bearing a Co(II)S 4 core, was the first mononuclear 3d metal complex to exhibit slow relaxation of its magnetization in the absence of a Direct Current (DC) magnetic field. [34][35][36][37] Along these lines, tetrahedral [Co{(EP i Pr 2 ) 2 N} 2 ], E = S, 38 Se, 38 Te, 39 complexes, bearing dichalcogenidoimidodiphosphinato ligands 40 and Co(II)E 4 cores, exhibit slow relaxation of their magnetization, which was also observed in the absence of DC magnetic field for the E = Se, Te, complexes. On the other hand, high-spin, S = 3/2, octahedral Co(II) complexes exhibit magnetic anisotropy that can be tuned through appropriate structural modifications, for instance axial elongation or compression of an octahedral coordination sphere, leading to axial anisotropy (very small Δ rh ) and the presence of either easy axis (Δ ax < 0) or easy plane (Δ ax > 0), of magnetization, respectively (Δ ax is the axial and Δ rh the rhombic crystal field parameter, vide infra).…”