A new lanthanum coordination polymer built from a semi-rigid tripodal carboxylic acid ligand: synthesis, crystal structure and properties

By employing the semi-rigid multidentate carboxylic acid ligand 4,4',4''-{[(2,4,6-trimethylbenzene-1,3,5-triyl)tris(methylene)]tris(oxy)}tribenzoic acid (denoted H₃L), a new lanthanum coordination polymer, namely poly[[bis(dimethylformamide)(μ₆-4,4',4''-{[(2,4,6-trimethylbenzene-1,3,5-triyl)tris(methylene)]tris(oxy)}tribenzoato)lanthanum(III)] dimethylformamide tetrasolvate 0.25-hydrate], {[La(C₃₃H₂₇O₉)(C₃H₇NO)₂]·4C₃H₇NO·0.25H₂O}_n or {[La(L)(DMF)₂]·4(DMF)·0.25(H₂O)}_n (DMF is dimethylformamide) (1), was prepared and characterized by single-crystal X-ray diffraction, elemental analysis, thermogravimetric analysis, IR spectroscopy and photoluminescence studies. The asymmetric unit contains one La^III cation, one anionic L^3- ligand, two coordinated DMF molecules, four free DMF molecules and one-quarter of a free water molecule. Compound 1 possesses (3,6)-connected two-dimensional kgd topology sheets consisting of secondary building units of La₂ clusters and L^3- ligands, which further stack into three-dimensional supramolecular networks through π-π interactions. Compound 1 exhibits a photoluminescence emission at room temperature, with a peak at 410 nm, owing to a ligand-centred excited state.