Optimizing the Hydrogen-Bond Network Drives Cadmium Ce(IV) Fluoride Hydrate with Significantly Enhanced Optical Anisotropy.

The controlled engineering of ordered crystal structures has emerged as a powerful strategy for the development of functional materials with enhanced optical properties. Herein, three novel cadmium Ce(IV) fluoride hydrates─Cd2CeF8(H2O)6, Cd2Ce3F16(H2O)8, and CdCeF6(H2O)2─have been obtained by simple hydrothermal methods. Birefringence calculations reveal a progressive increase in Δn values: 0.009@546 nm for Cd2CeF8(H2O)6, 0.042@546 nm for Cd2Ce3F16(H2O)8, and 0.147@546 nm for CdCeF6(H2O)2. The measured birefringence of CdCeF6(H2O)2 reaches 0.152@546 nm, surpassing most known rare-earth fluorides. Combined structural and theoretical investigations demonstrate that the observed enhancement originates from the concerted alignment of anisotropic [(CeF6)2-]∞ chains and {[Cd(H2O)2]2+}∞ chains mediated by hydrogen-bonding networks, synergistically coupled with ordered interlayer stacking configurations. This work enriches the diversity of rare-earth fluorides, promoting further research into the development of promising rare-earth fluoride birefringent materials.