Magnetic anisotropy and structural flexibility in the field-induced single ion magnets [Co{(OPPh(2))(EPPh(2))N}(2)], E = S, Se, explored by experimental and computational methods

During the last few years, a large number of mononuclear Co(ii) complexes of various coordination geometries have been explored as potential single ion magnets (SIMs). In the work presented herein, the Co(ii) S = 3/2 tetrahedral [Co{(OPPh(2))(EPPh(2))N}(2)], E = S, Se, complexes (abbreviated as CoO(2)E(2)), bearing chalcogenated mixed donor-atom imidodiphosphinato ligands, were studied by both experimental and computational techniques. Specifically, direct current (DC) magnetometry provided estimations of their zero-field splitting (zfs) axial (D) and rhombic (E) parameter values, which were more accurately determined by a combination of far-infrared magnetic spectroscopy and high-frequency and -field EPR spectroscopy studies. The latter combination of techniques was also implemented for the S = 3/2 tetrahedral [Co{(EP(i)Pr(2))(2)N}(2)], E = S, Se, complexes, confirming the previously determined magnitude of their zfs parameters. For both pairs of complexes (E = S, Se), it is concluded that the identity of the E donor atom does not significantly affect their zfs parameters. High-resolution multifrequency EPR studies of CoO(2)E(2) provided evidence of multiple conformations, which are more clearly observed for CoO(2)Se(2), in agreement with the structural disorder previously established for this complex by X-ray crystallography. The CoO(2)E(2) complexes were shown to be field-induced SIMs, i.e., they exhibit slow relaxation of magnetization in the presence of an external DC magnetic field. Advanced quantum-chemical calculations on CoO(2)E(2) provided additional insight into their electronic and structural properties.