Molecular Engineering of Dysprosium Complexes for Tunable Magnetic Anisotropy and Luminescent Thermometry

Harnessing and tailoring spin dynamics at the molecular level is pivotal for advancing quantum information technologies and multifunctional materials. While α-diimine–Dy(III) β-diketonates have been extensively explored, β-diimine ligands remain largely unexplored as a ligand-field platform for modulating magnetic anisotropy and magneto-optical response in Dy(III) β-diketonates. Herein, we investigate β-diimine coligands as a tunable ligand-field platform in Dy(III) β-diketonate complexes, [Dy(dbm)3(bik-Et)] (1), [Dy(dbm)3(bik-Me)] (2), and [Dy(acac)3(bik-Et)] (3), where bik-R = bis(1-R-1H-imidazol-2-yl)methanone. Single-crystal X-ray diffraction reveals DyO6N2 coordination in distorted square antiprismatic (1, 3) and triangular dodecahedral (2) geometries, leading to distinct anisotropy-axis orientations. All complexes exhibit zero-field slow magnetic relaxation, and ab initio CASSCF/SINGLE_ANISO calculations reproduce Kramers doublet splitting and show qualitative correlations between coordination structure, electronic anisotropy, and relaxation pathways. Temperature-dependent photoluminescence demonstrates that these complexes function as luminescent thermometers with high relative sensitivity up to 2.98% K–1. Together, these results establish β-diimine coordination as a complementary ligand-field platform for modulating coordination geometry, Kramers-doublet structure, magnetic anisotropy, relaxation behavior, and luminescent thermometry in Dy(III) β-diketonate single-ion magnets.