Molecular based spin qubits of Mn(II) coordination compounds with S = 5/2.

Spin qubits based on electron spins are promising platforms for quantum information science due to their ability to form controllable superposition states with long coherence times. While most molecular spin qubits have focused on S = 1/2 systems, high-spin systems offer an alternative approach with access to multilevel quantum states. In particular, high-spin Mn(II) (S = 5/2) centers possess zero orbital angular momentum (L = 0), resulting in weak spin-orbit coupling that suppresses spin-lattice relaxation and prolongs phase memory times. The central transition (MS = -1/2 ↔ +1/2) behaves similarly to an S = 1/2 system, enabling robust and stable spin coherence, whereas the outer transitions (MS = ±5/2 ↔ ±3/2 and ±3/2 ↔ ±1/2) provide additional functionality through interactions with nuclear spin systems and external electric fields. Recent studies on Mn(II)-doped metal-organic frameworks and discrete Mn(II) complexes diluted in diamagnetic matrices demonstrate tunable spin relaxations, highlighting their potential as multilevel quantum units for advanced quantum operations such as Grover-type algorithms. Despite these promising features, molecular high-spin qubits remain less explored than their S = 1/2 counterparts, and further investigations into spin-vibration coupling, structural design, and external field control are required. Overall, high-spin metal complexes represent an emerging and versatile platform for next-generation spin-based quantum technologies.