Synthesis, structure and fluorescence of three novel Ln(III) polymers based on a semi-rigid tetracarboxylic acid

Three novel Ln(III) polymers based on a same semi-rigid tetracarboxylic acid H 4 BTMIPA (5,5′-methylenebis(2,4,6-trimethylisophthalic acid)), namely [Gd(HBTMIPA)(H 2 O) 2 OH]H 2 O (1), [H 2 N(CH 3 ) 2 ][Gd(H 2 O) 2 (BTMIPA)]2H 2 O(2), [H 2 N(CH 3 ) 2 ][Sm(H 2 O) 2 (BTMIPA)]2H 2 O(3) (H 4 BTMIPA=(5,5′-methylenebis (2,4,6-trimethylisophthalic acid)) were synthesized by regulating the preparation method and metal center. All three complexes feature a nine-coordinate metal center but exhibit distinct structures. Complex 1, obtained via biphasic solvothermal reaction, is constructed by HBTMIPA ligands linking three Gd 3+ ions through chelating carboxylate groups, forming 1D wavy chains. These chains further assemble into 2D layers and eventually a 3D supramolecular structure with helical characteristics via hydrogen bonds. Complex 2 and 3 are isostructural which prepared by solvothermal reaction, form 3D supramolecular structures with 1D channels. Their IR spectra, PXRD, thermal stability and photoluminescence properties were investigated. This work demonstrates that the biphasic solvothermal method enables the generation of novel frameworks with unique structures, providing insights for developing new Ln-MOFs.