In the present work, we report the synthesis of isomeric heteronuclear terbium(III) and yttrium(III) triple-decker phthalocyaninates[(BuO)8Pc]M[(BuO)8Pc]M*[(15C5)4Pc](M = Tb, M* = Y or M = Y, M* = Tb, [(BuO)8Pc]2−–octa-n-butoxyphthalocyaninato-ligand, [(15C5)4Pc]2−–tetra-15-crown-5-phthalocyaninato-ligand). We show that these complexes undergo solvation-induced switching: the conformers in which both metal centers are in square-antiprismatic environments are stabilized in toluene, whereas in dichloromethane, the metal centers M and M* are in distorted prismatic and antiprismatic environments, respectively. This conclusion follows from the detailed analysis of lanthanide-induced shifts in1H NMR spectra, which makes it possible to extract the axial component of the magnetic susceptibility tensorχaxTband to show that this term is particularly sensitive to conformational switching when terbium(III) ion is placed in the switchable “M” site. This result provides a new tool for controlling the magnetic properties of lanthanide complexes with phthalocyanine ligands.