Synthesis, structure and magnetic properties of tris(pyrazolyl)methane lanthanide complexes: Effect of the anion on the slow relaxation of magnetization

We report on the synthesis, structure and investigation of magnetic properties of a series of six heteroleptic complexes of the general formula [Ln(Tpm)X₃]·yMeCN (Tpm = tris(3,5-dimethylpyrazolyl)methane; Ln = Tb, Dy, Er; X^- = NO₃ ^-, Cl^- and y = 1 or 2). We demonstrate that the observation of a field-induced slow relaxation of magnetization is highly dependent on the anion's nature. While nitrate moieties appear to be suitable to stabilize the oblate electronic density of Dy³⁺, chloride ions generate an equatorial crystal-field allowing the slow relaxation of the prolate Er³⁺ ions.