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

While most research on molecule-based electron spin qubits has focused on S = 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), 1Si-Gd and 1Ge-Gd. Pulsed EPR measurements reveal spin-lattice relaxation (T1) and quantum coherence (Tm) 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 1Si-Gd and 1Ge-Gd 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.