The pyrazole-based tridentate diol ligand 2-(1-(2-hydroxyethyl)-1H-pyrazol-3-yl)phenol (H2L) forms a cubane-type complex [Co4L4(MeOH)4] (1) that features a {Co4O4} core and four exogenous MeOH ligands. Electrospray ionization mass spectrometry suggests that the MeOH ligands are easily lost, and thermogravimetric analysis evinces a thermally induced release of those methanol molecules from solid material in the temperature range from 380 to 440 K. Desolvation was found to give rise to a pronounced solvatomagnetic effect that causes a switching of the spin ground state of the {Co4O4} core from diamagnetic to magnetic. Furthermore, the desolvated "naked" [Co4L4] cube (1*) shows slow relaxation of the magnetization and butterfly-like magnetic hysteresis at 2 K. A comparatively high relaxation barrier Ueff/kB = 64.4 K and a characteristic relaxation time τ0 = 3.8 × 10(-9) s for 1* have been derived from an Arrhenius plot. These findings thus demonstrate that the emergence of interesting magnetic properties in molecule-based materials can be triggered via a solvatomagnetic process, even for materials that in their solvated form have a diamagnetic (ST = 0) ground state.