Deferasirox HOF and its in situ metallization enabling a new family of lanthanide coordination polymer-based MHOFs

Abstract

Pure organic HOFs (hydrogen-bonded organic frameworks) lack the stronger coordination bonds and some functional sites attached to their parent structures. It is important to graft functional metal ions into single HOF structure via coordination bonds in order to develop highly stable and multifunctional MHOFs (metallo hydrogen-bonded organic frameworks). Used as a trifurcated hydrogen-bonded linking agent, deferasirox (DFX) is suitable for the construction of dual-self-complementary HOF. In the absence of deprotonated reagent, in situ metallization of DFX HOF with lanthanide ions in aqueous solution directly produces a new family of lanthanide coordination polymer-based MHOFs formulated as [Ln2(μ-H2O)(μ-H2L)6]n (Ln = Ce (DFX-Ce), Eu (DFX-Eu), Gd (DFX-Gd)) and [Tb4(μ-H2O)2(μ-H2L)10(H2O)(H2L)2]2n (DFX-Tb) (H2L=4-[3,5-bis(2-hydroxyphenyl)-1,2,4-triazol-1-yl]-benzoate anion). The structural determination reveals that four new compounds present the cruciform-like 1D coordination polymer chains featured with the MHOF structures due to the pendant flexible-robust phenol groups. Solid state photoluminescence for DFX-Ce exhibits the dominated emission of the free DFX ligand accompanied by the 5d → 4f transitions of Ce3+. While DFX-Eu and DFX-Tb display the obviously characteristic emissions for the corresponding lanthanide ions based on 4f → 4f transitions. In particularly, since the lowest triplet state energy levels of the DFX ligand match well to the resonance level of Tb3+, DFX-Tb has highly efficient photoluminescence compared with DFX-Eu. The strongly emissive characteristic of DFX-Tb makes it a potential application in fluorescent materials. Furthermore, magnetic property studies for DFX-Gd reveal the weak antiferromagnetic interaction between neighboring Gd3+ ions, and the significant magnetocaloric effect with a large magnetic entropy change. To the best of our knowledge, no any lanthanide coordination polymers are successfully synthesized from the ligand DFX or its derivatives thus far, and the presented in situ metallization of the DFX HOF with the corresponding lanthanide ions provides a new route to synthesize lanthanide coordination polymer-based MHOFs with interesting structures and multifunctional properties in future.