Polymorphism from a 1:1 Ln:BTB reaction pot: Solvothermal versus sonochemical synthesis of Ln-MOFs

• Published in: Inorganica Chimica Acta Vol. 546; p. 121299
• Main Authors: Smith, Jermaine A., Singh-Wilmot, Marvadeen A., Min, Zeyar, Carter, Korey P., Gilbert, Saddi, Andrews, Michael B., Ridenour, J. August, Cahill, Christopher L., Ley, Amanda N., Holman, K. Travis
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.02.2023
• Subjects: Benzenetrisbenzoate (BTB); Fluorescence sensor; Lanthanide; Metal-organic framework; Polymorphs; Solvothermal; Sonochemical; Benzenetrisbenzoate (BTB); Lanthanide; Polymorphs; Solvothermal; Metal-organic framework; Fluorescence sensor; Sonochemical
• ISSN: 0020-1693; 1873-3255
• DOI: 10.1016/j.ica.2022.121299

A 1:1 reaction pot of Ln:BTB in a 2:1 mixture of DMF/H2O yields three different Ln-BTB polymorphs when subjected to solvothermal and sonochemical conditions. [Display omitted] •A Ln:BTB reaction with identical constituents produces three different polymorphs of Ln-BTB frameworks under varying conditions.•The solvothermal reaction is temporally modulated yielding a novel 3D MOF and new analogues of a known phase.•The third polymorph was made by sonochemical synthesis for the first time.•One polymorph shows promising H2 adsorption and potential as a luminescence sensor for Fe3+ and nitroaromatics. A 1:1 reaction pot of lanthanide(III):1,3,5-benzenetrisbenzoate (Ln(III):BTB) in a 2:1 mixture of DMF/H2O was subject to solvothermal and sonochemical conditions in order to form new Ln-BTB polymorphs. Solvothermal crystal growth is time dependent, yielding a new MOF structure Nd4(BTB)4(H2O)10•(H2O)7 (1) after 1–2 days and two new analogues of Ln(BTB)(H2O), Nd(BTB)(H2O) (2) and Sm(BTB)(H2O) (3) after 3.5 days. Sonochemical synthesis produced a pure phase of Ln(BTB)(H2O)2•(H2O)2(DMF)3 (4–7, Ln = Nd3+ (4), Eu3+ (5), Tb3+ (6), and Er3+ (7)). Compound 1 is a novel 3-D framework that consists of undulating one-dimensional lanthanide-carboxylate secondary building unit (SBU) chains connected by BTB linkers, which pack into a hxl topology with rhombohedral and hexagonal channels. The total solvent accessible void space is 4581.6 Å3 which constitutes 37 % of the of the total unit cell volume. Compounds 2 and 3 are three-dimensional microporous networks consisting of mutually parallel-perpendicular, infinite, undulating one-dimensional metal-carboxylate SBU chains interlinked by BTB ligands. Compounds 4–7 were previously reported from four different synthetic protocols and feature Ln2(COO)6(H2O)4 SBUs linked by BTB linkers into a two-dimensional (3,6-connected) kgd network, which assembles via hydrogen bonds into a three-dimensional supramolecular framework. Gas adsorption studies on compound 4 indicate microporous and mesoporous sites that contribute relatively high Langmuir and BET surface areas up to 1161 m2/g and 671 m2/g, respectively. Eu(BTB)(H2O)2•(H2O)2(DMF)3 (5) displays strong luminescence under UV excitation and is a highly sensitive and selective sensor for Fe3+ ions and nitroaromatic compounds. Sensing occurs via luminescence quenching due to competitive absorption of excitation energy between the BTB framework and the analyte molecules.