Approaching the free-ion limit in magnetically isotropic gadolinium(III) via borohydride ligands

Three new crystalline phases of the borohydride complex, [n-Bu4N][RE(BH4)(4)] (RE = Gd (1), Gd0.097Y0.903 (2) and Gd0.017Y0.983 (3)), were obtained in pure form and characterised using EPR spectroscopy and AC/DC magnetometry. In all 1-3, unusually slow field-induced magnetic relaxation was observed up to high temperatures, which above 10 K is dominated by power law thermal dependence identified as the two-phonon Raman process. Therefore, weak-field ligands such as borohydride seem to be the perfect candidates for triggering slow magnetic relaxation of magnetically isotropic gadolinium(iii) ions.