A Stable Radical in Cationic Dinuclear Rare-Earth Triple-Decker Complexes Featuring Switchable Magnetic Properties

In quantum information processing, the implementation of qudits─multilevel qubits where d is the number of levels─has been a major challenge that, if resolved, could lead to the acceleration of certain computational tasks. Spin transport measurements demonstrate that tris(phthalocyaninato)-dinuclear rare-earth(III) molecules offer a promising platform for nuclear spin qudits with an increased Hilbert space. However, the absence of radicals in these systems has so far hindered studies on the coupling between lanthanide ions and conduction electrons. In this study, we report the synthesis of (phthalocyaninato)bis(porphyrinato)-dinuclear rare-earth(III) complexes functionalized with thiomethyl groups. The tailored oxidation of the neutral complexes facilitated their conversion to air-stable radicals. CASSCF calculations and static magnetic measurements revealed a radical-lanthanide exchange coupling constant of J_Ln-Rad = -0.45 cm^-1. Dynamic magnetic measurements demonstrated a shift in the magnetic properties due to exchange interaction, namely from field-induced single-molecule magnets (SMMs) to zero-field SMMs. The findings of this study, along with the strong bonding affinity of thiomethyl groups to gold electrodes, highlight the potential of these molecules as novel materials for the implementation of nuclear spin qudits with an increased Hilbert space.