Controllable Solid-State Transformations and Enhanced Luminescence of Labile Lanthanide(III) Aquanitrato Complexes Anchored within a Hydrogen-Bonded Organic Matrix.

Two structural types of lanthanide (Ln) aquanitrato complexes incorporating 1,4-diazabicyclooctane-N,N'-dioxide (odabco) were synthesized and structurally characterized by single-crystal X-ray diffraction (SCXRD). Phase 1Ln comprises (Hodabco)3[Ln(H2O)2(NO3)4](NO3)2 (Ln3+ = Eu3+, Gd3+, (Eu/Gd)3+, Tb3+) while phase 2Ln represents (Hodabco)3[Ln(H2O)(NO3)5](NO3) (Ln3+ = Eu3+, (Eu/Gd)3+). Due to a shared cationic network composition and coordination isomerism, these Ln-based phases exhibit reversible, solvent-driven structural transitions, fully confirmed by powder XRD. Despite the presence of quenching aqua ligands, the complexes display remarkable photoluminescence with quantum yields up to 40%. The structural transitions induce a 4-fold modulation of photoluminescence quantum yields and a 2-fold variation in excited-state lifetimes. These findings establish a robust strategy for the targeted control of Ln(III) emission via simple chemical stimuli, offering strong potential for chemical sensing and luminescent device design.