A Dual-Purpose Ce(III)-Organic Framework with Amine Groups and Open Metal Sites: Third-Order Nonlinear Optical...

The present work focuses on the synthesis and properties of a novel multifunctional cerium(III) MOF, [Ce₂(data)₃(DMF)₄]·DMF (data^2-: 2,5-diaminoterephthalate), abbreviated as NH₂-Ce-MUM-2. Its crystal structure reveals an intricate 3D 4,5-connected framework with a xah topology. This MOF features unique properties, such as open metal sites, presence of free amino groups, and high stability. Two main applications of NH₂-Ce-MUM-2 were investigated: (i) as a heterogeneous catalyst in the CO₂ fixation into cyclic carbonates and (ii) as a material with third-order nonlinear optical activity. As a model reaction, the cycloaddition of CO₂ to propylene oxide to give the corresponding cyclic carbonate was explored under mild conditions, at the atmospheric pressure of carbon dioxide and in the absence of cocatalyst and added solvent. Various reaction parameters were investigated toward optimization and exploration of substrate scope, revealing up to 99% product yields of cyclic carbonate products. Besides, the structure of NH₂-Ce-MUM-2 is highly stable, permitting its recyclability and reusability in further catalytic experiments. The significant contributions of free amino groups and open metal sites within this catalyst were particularly considered when proposing a potential mechanism for the reaction. Z-Scan measurements were used to evaluate the nonlinear optical (NLO) properties of NH₂-Ce-MUM-2 at various laser intensities. A high two-photon absorption (TPA) under greater incident intensities shows that NH₂-Ce-MUM-2 might be applicable in optical switching devices. Besides, the self-focusing effects of NH₂-Ce-MUM-2 under various incident intensities were highlighted by the nonlinear index of refraction (n₂). By reporting the synthesis and characterization of a novel MOF, along with its highly promising catalytic and NLO behavior, the current study introduces an additional example of multifunctional material into a growing family of metal-organic frameworks.