Coherent Spin Manipulation in Mononuclear Gadolinium-Substituted Polyoxometalate–Organic Hybrids

While most research on molecule-based electron spin qubits has focused on <i>S</i> = 1/2 ions for single-qubit gates, the need for qubit interactions in quantum operations has driven interest in higher-spin molecules and multilevel states. Herein, we study the spin dynamics of two mononuclear gadolinium-substituted polyoxometalate-organic hybrids with the general formula K₅[Gd(α-XW₁₁O₃₉)(H₂L)]·14H₂O (X = Si, Ge; H₂L = N,N'-dimethyl-N,N'-bis(2-hydroxy-3-formyl-5-bromobenzyl)ethylenediamine), <b>1</b>_<b>Si</b><b>-Gd</b> and <b>1</b>_<b>Ge</b><b>-Gd</b>. Pulsed EPR measurements reveal spin-lattice relaxation (<i>T</i>₁) and quantum coherence (<i>T</i>_m) times of up to 2315 and 2.6 μs at 3 K, respectively, for diamagnetically diluted samples, as well as Rabi oscillations up to 20 K. The obtained results make <b>1</b>_<b>Si</b><b>-Gd</b> and <b>1</b>_<b>Ge</b><b>-Gd</b> two of the few Gd-based complexes displaying such behavior, highlighting the challenge of coherently manipulating the spin states of Gd. Moreover, their hybrid organic-inorganic nature endows them with chemical robustness and solution stability, essential prerequisites for surface immobilization and future integration in practical devices.