Chemically Tunable Spin Frustrated Triangles as New Candidates for Molecular Spin Qubits

Molecular spin triangles have been theoretically predicted to exhibit spin electric coupling (SEC) holding significant promising in quantum information technology. The possibility of nanoscale manipulation of spin states by the application of electric field offers several advantages over the standard magnetic field-based control of spin states. Experimentally, the antiferromagnetically coupled spins systems arranged in a triangular cluster (M₃) where M = Cu²⁺, Co²⁺, Fe³⁺ have been explored to reveal spin electric coupling by utilizing voltage pulses for modulating the phase accumulation within spin-echo sequences in pulsed electron paramagnetic resonance (EPR) experiments. Despite the rapid experimental progress in this field in last one decade, the role of spin anisotropy, antisymmetric exchange interactions and structural distortions in driving the strength of magnetoelectric coupling effects remains underexplored. Here we report an isostructural series of molecular spin triangles based on triaminoguanidine ligand scaffold with metal centres as Cu²⁺ (S = 1/2, complex 1), Co²⁺ (S = 3/2, complex 2), and Mn²⁺ (S = 5/2, complex 3) ions laying groundwork for chemically tunable magnetoelectric spin qubits. Herein, for the first time, we report the antiferromagnetically coupled Mn₃ triangle by incorporating the triaminoguanidine ligand motif. DFT calculations reveal distinct magnetic exchange coupling strengths among the Mn₃, Co₃, and Cu₃ spin triangles. Continuous-wave (cw) EPR spectroscopy reveals a paramagnetic ground state for all M₃ triangle studied for the antiferromagnetically coupled clusters with half integer spin on each metal ion. Pulsed EPR measurements establish microsecond phase memory times (T₂ ~ 0.8–2.3 μs) and long spin-lattice relaxation times for all three complexes at cryogenic temperatures, confirming the quantum coherence prerequisites for spin-electric coupling (SEC) detection. This series spanning S = 1/2, 3/2, and 5/2 within a single structural scaffold provides a chemically controlled platform for systematically disentangling the microscopic contributions to spin electric coupling across the 3d transition metal series.