| Summary: | In the present work, we report the synthesis of isomeric heteronuclear terbium(III) and yttrium(III) triple-decker phthalocyaninates <b>[(BuO)<sub>8</sub>Pc]M[(BuO)<sub>8</sub>Pc]M*[(15C5)<sub>4</sub>Pc]</b> (M = Tb, M* = Y or M = Y, M* = Tb, [(BuO)<sub>8</sub>Pc]<sup>2−</sup>–octa-<i>n</i>-butoxyphthalocyaninato-ligand, [(15C5)<sub>4</sub>Pc]<sup>2−</sup>–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 in <sup>1</sup>H NMR spectra, which makes it possible to extract the axial component of the magnetic susceptibility tensor <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msubsup><mrow><mi mathvariant="sans-serif">χ</mi></mrow><mrow><mi>ax</mi></mrow><mrow><mi>Tb</mi></mrow></msubsup></mrow></semantics></math></inline-formula> and 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.
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