Chemical tuning of quantum spin–electric coupling in molecular magnets

nature chemistry Article https://doi.org/10.1038/s41557-025-01926-5 Chemical tuning of quantum spin–electric coupling in molecular magnets Received: 31 October 2024 Accepted: 23 July 2025 Mikhail V. Vaganov 1,6, Nicolas Suaud 2,6, François Lambert3,6, Benjamin Cahier2, Christian Herrero3, Régis Guillot3, Anne-Laure Barra4, Nathalie Guihéry2 , Talal Mallah3 , Arzhang Ardavan 1 & Junjie Liu 1,5 Published online: xx xx xxxx Check for updates Controlling quantum spins using electric rather than magnetic fields promises substantial architectural advantages for developing quantum technologies. In this context, spins in molecular magnets offer tunability of spin–electric couplings (SECs) by rational chemical design. Here we demonstrate systematic control of SECs in a family of Mn(II)-containing molecules by varying the coordination environment of the spin centre. The trigonal bipyramidal (tbp) molecular structure with C3 symmetry leads to a substantial molecular electric dipole moment that is directly connected to its magnetic anisotropy. The interplay between these two features gives rise to experimentally observed SECs, which can be rationalized by wavefunction theoretical calculations. Our findings guide strategies for the development of electrically controllable molecular spin qubits for quantum technologies. The possibility of electrical spin control offers substantial architectural advantages for classical or quantum spintronics because, compared to magnetic fields, electric fields can be efficiently routed and confined in complex nanoscale circuits, thereby reducing energy consumption and facilitating logic operations on spins1–5. Research into interactions between electric fields and spin degrees of freedom in various quantum systems have attracted interest both theoretically and experimentally6–12. A strong spin–electric coupling (SEC) is critical both for efficient electrical quantum spin control and for engineering coherent spin–electric interfaces that allow the exchange of quantum information between distinct spin qubits13,14. Among the candidates for spin qubits, molecular magnets offer particular advantages: coordination chemistry allows rich tunability of molecular quantum spin structures while also providing routes to large-scale integration via supramolecular approaches15–18. One approach to enhancing SECs in molecular magnets19–22 is to exploit strong spin–orbit coupling (SOC) by employing heavy metals, such as rare earth atoms, as the spin carrier. For example, a Ho(III)-containing molecular magnet, in which a small structural distortion from strict tetragonal symmetry leads to an E-field-sensitive spin transition, demonstrates a SEC that is sufficiently strong to enable selective spin control using modest electric fields of 105 V m−1 (ref. 22). Although providing important insights, the Ho(III) example also highlights a limitation of this approach: such molecules typically possess a giant ligand field-induced magnetic anisotropy, leading to inconveniently large transition energies between spin states. Furthermore, the origin of the SEC in this system is an accidental symmetry-breaking, rather than the result of rational chemical design. We thus identify a challenge of engineering molecular magnets with spin transitions that are both in an accessible energy range and sensitive to electric fields. The S = 5/2 spin associated with a Mn(II) ion is a simple quantum system with potential for quantum information processing (QIP). As a free ion, it has a half-filled 3d shell with an electron ground state of S = 5/2 and L = 0. In molecular or crystalline environments, the weak SOC leads to small magnetic anisotropies, reduced spin–lattice relaxation and impressive spin relaxation times. It also removes one of the key ingredients for enhancing SEC, at first sight compromising the scope for efficient E-field spin control23–25. Indeed, so far, a sizable SEC in CAESR, Department of Physics, University of Oxford, The Clarendon Laboratory, Oxford, UK. 2Laboratoire de Chimie et Physique Quantiques (LCPQ), Université de Toulouse, CNRS, Toulouse, France. 3Institut de Chimie Moléculaire et des Matériaux d’Orsay, Université Paris-Saclay, CNRS, Orsay, France. 4 Laboratoire National des Champs Magnétiques Intenses, CNRS, Université Grenoble Alpes, Grenoble, France. 5School of Physical and Chemical Sciences, Queen Mary University of London, London, UK. 6These authors contributed equally: Mikhail V. Vaganov, Nicolas Suaud, François Lambert. e-mail: ; ; ; 1 Nature Chemistry Article https://doi.org/10.1038/s41557-025-01926-5 a b c Side view N1 2, T1 N2 0 Mn 0.1 0.2 0.3 0.4 0.5 X Top view 0.6 0.7 0.8 0.9 Single crystal, 3.5 K 34.0 GHz 0.5 1.0 1.5 Powder, 5 K 255.4 GHz C X Mn 1, Tm 2, Tm 2 10 10 1 0 N Relaxation times (µs) 10 ESR spectra (a.u.) N2 1, T1 3 8.2 8.4 8.6 8.8 9.0 9.2 Magnetic field (T) 9.4 9.6 10 Stretch parameter N2 4 10 Powder, 90 K 9.6 GHz –1 3 1 2 2 1 0 0 5 10 15 20 25 Temperature (K) Fig. 1 | ESR spectra and spin relaxation measurements for 1 and 2. a, Ball-andstick representation of the [Mn(me6tren)X] molecules. H atoms are omitted for clarity. b, Representative low-temperature ESR spectra for 1 recorded with different sample forms at different frequencies. The single-crystal spectrum (middle) was recorded at the Q-band using an echo-detected field sweep (EDFS), whereas the ESR experiments for the powder sample (top and bottom) were conducted using the continuous-wave method. c, Low-temperature relaxation times for 1 and 2 molecules measured on the −5/2 ↔ −3/2 and +3/2 ↔ +5/2 transitions, respectively. Upper panel: the spin–lattice relaxation time, T1, and quantum phase memory time, Tm, for 1 and 2 as a function of temperature. T1 is described by a single exponential decay over the experimental temperature range. Lower panel: in contrast, Tm follows a stretched exponential, whose stretch parameter varies with temperature. Mn(II) has only been observed when doped into ferro- or piezoelectric hosts26 offering little scope for tuning the spin properties. In this Article we exploit the chemical control over the coordination sphere available in a family of molecular magnets containing Mn(II) to engineer SECs. Our strategy is to design a molecular geometry, namely [Mn(me6tren)X]Y (where me6tren is tris[2-(dimethylamino) ethyl]amine, X = Cl, Y = ClO4 (1), X = Br, Y = PF6 (2) and X = I, Y = I (3)), which, by virtue of its substantial in-built electric dipole, exhibits a substantial E-field-induced deformation that is also coupled to the molecular spin anisotropy. The effect of the electric field in our complexes manifests as a variation of the zero-field splitting (ZFS) parameter D, which is the SEC measured in this work. This approach yields molecular SECs comparable with those only observed so far for lanthanide-based molecules with strong SOC. Our rational design approach allows us to tune the (...truncated)