Spin-canted Mn–Mn coupling in symmetry-broken metal chloride dimer with dual-responsive luminescence and sensing

Abstract Magneto-optical coupling provides a powerful alternative to crystal field engineering for modulating Mn 2+ luminescence. However, precise control over Mn–Mn coupling is hindered by the complex spin-electron super-exchange interactions. Herein, we report a symmetry-broken Mn(II) chloride dimer, (C 10 H 20 O 5 Mn)(CH 3 CN)MnCl 4 , synthesized through a crown-ether-assisted supramolecular strategy. The dimer features a 7-coordinated pentagonal bipyramid and a 4-coordinated tetrahedron linked by a distorted Mn–Cl–Mn bridge (129°), which promotes rare spin-canted Mn–Mn coupling and creates a novel Mn–Mn luminescent center. This center exhibits a red emission at 638 nm with an unusually short lifetime of 0.42 ms, which is attributed to the relaxation of spin-forbidden d – d transitions. Notably, the emission undergoes a 30 nm blue-shift upon heating (5–305 K) due to the thermal suppression of spin-canting, and a 40 nm blue-shift under applied pressure (0–20 MPa) resulting from reduced orbital overlap. This dual-responsive luminescence originates from spin-canted weak ferromagnetism, which induces a rearrangement of energy-levels by separating antibonding orbitals. Using this effect, we have demonstrated an optical manometer for real-time underwater depth sensing. These findings highlight spin-canted Mn(II) dimers as a promising platform for stimuli-responsive luminescence and reveal a new mechanism for d–d transition modulation.