Lanthanide coordination polymers with hexa-carboxylate ligands derived from cyclotriphosphazene as bridging linkers: synthesis, thermal and luminescent properties

Abstract

Solvothermal reactions of two ligands with different geometries, derived from cyclotriphosphazene, hexakis(4-carboxylato-phenoxy)cyclotriphosphazene (H₆L1) and hexakis(3-carboxylato-phenoxy)cyclotriphosphazene (H₆L2) with Eu(NO₃)₃·6H₂O in H₂O/DMF under similar synthesis conditions produced three new compounds, namely, {[Eu₂(L1)(H₂O)₄]·(H₂O)₄·(DMA)₂}_n (1), {[Eu₂(L1)(H₂O)₈]·(H₂O)₂·DMA}_n (2), and {[Eu₂(L2)(H₂O)₃(DMF)]·(H₂O)₂·(DMA)}_n (3). Compounds 1 and 2 display a 2D layer crystal structure with a distinct topological network incorporating the extended hexa-carboxylate ligand L1; in contrast, 3 has a 1D crystal structure with the highly distorted hexa-carboxylate ligand L2. In these three compounds, the ligands L1 and L2 are fully deprotonated, whose six extended carboxyl arms connect six different/same metallic nodes to generate metal–organic frameworks. The luminescence properties of three compounds have been studied at room temperature in relative detail.