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

Solvothermal reactions of two ligands with different geometries, derived from cyclotriphosphazene, hexakis(4-carboxylato-phenoxy)cyclotriphosphazene (H(6)L1) and hexakis(3-carboxylato-phenoxy)cyclotriphosphazene (H(6)L2) with Eu(NO3)(3)center dot 6H(2)O in H2O/DMF under similar synthesis conditions produced three new compounds, namely, {[Eu-2(L1)(H2O)(4)]center dot(H2O)4 center dot(DMA)(2)}(n) (1), {[Eu-2(L-1)(H2O)(8)]center dot(H2O)(2)center dot DMA}(n) (2), and {[Eu-2(L-2)(H2O)(3)(DMF)]center dot(H2O)(2)center dot(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.