Magnetic Dynamics and Elongated Coherence of a High‐Spin Mn(II) Qubit Doped Into a Metal‐Organic Framework

Spin qubits are among the most promising candidates for quantum information processing and sensing technologies. Their potential to function even at elevated temperatures makes them particularly attractive for future devices. However, while extensive studies have been carried out on S = 1/2 systems, high-spin complexes remain much less explored as spin qubit platforms. In this study, we prepared a Zn(II)-based MOF, [CH₆N₃][Zn(HCOO)₃], doped with trace amounts of Mn(II) ions (S = 5/2, 0.2, and 0.02 mol%). Magnetic measurements under static fields revealed slow relaxation phenomena dominated by direct and Raman-like processes. Importantly, Q-band pulsed ESR confirmed quantum coherence between M_S = ±1/2 sublevels, achieving phase memory times (T₂) up to 5.4 µs at 10 K, which is significantly longer than those reported in other Mn(II)-based systems. Rabi nutation experiments verified coherent spin control and multilevel transitions, while Wigner matrix analysis revealed reorientation of the nuclear quantization axis during spin flips. Notably, coherence persisted above 150 K, attributed to the stabilization provided in the MOF's hydrogen-bonded lattice. This work represents the first demonstration of high-spin Mn(II) qubits with measurable coherence at elevated temperatures, underscoring MOFs as versatile and tunable platforms for advancing quantum materials and molecular spin-based technologies.