Lanthanide-Diphosphonate Frameworks Containing Dianthracene: Isolation of Metastable Intermediates and...

Capturing kinetic intermediates is crucial for understanding the formation mechanism of metal-organic frameworks (MOFs), but it is particularly challenging for metal phosphonate frameworks. Here, we employ a modulator-based strategy to control the crystallization of MOFs. By adding the chelating ligand shikimic acid, we obtained three-dimensional (3D) lanthanide-diphosphonate frameworks, [Ln₂(amp₂H₂)₃(H₂O)]·4H₂O (Ln-3D, x = 6, Ln = Sm, Eu, Gd, Tb, Ho; x = 4, Ln = Er), where amp₂H₄ is prephotodimerized 9-anthracenemethylphosphonic acid. By reducing the reaction temperature from 90 to 70 °C, we successfully isolated the metastable reaction intermediates, [Ln₂(amp₂H₂)₂(H₂O)₁₂](amp₂H₂)·10H₂O (Ln-1D), with one-dimensional (1D) chain structures. The dianthracene moiety in the linker amp₂H₂^2- confers additional dynamic features to the material due to its potential dissociation into anthracene pairs and affects the photophysical and photochemical properties, which vary with the lanthanide ion. Moreover, the labile coordinated water molecule in Ho-3D is releasable under X-ray irradiation at 300 K, whereas this X-ray responsiveness is not obvious for other Ln-3D (Ln = Sm, Eu, Gd, and Tb). This study not only provides a new case for metal phosphonate intermediate trapping but also demonstrates rare metal-organic materials with ultraviolet (UV) light and X-ray responsiveness.