Photoluminescent 3D lanthanide MOFs with a rare (10,3)-d net based on a new tripodal organic linker

A new semi-rigid tripodal ligand, namely 1,1′,1″-((2,4,6- triethylbenzene-1,3,5 triyl)tris(methylene))tris(pyridin-4(1H)-one) (L1), has been prepared by direct alkylation of 4-hydroxypyridine at the nitrogen site with 1,3,5-tris(bromomethyl)-2,4,6-triethylbenzene. The tripodal ligand has been used for the assembly of a series of isomorphous lanthanide metal-organic frameworks (Ln-MOFs) [Ln(L1)·(NO₃)₃]·nH ₂O (Ln = Eu (1), Tb (2), Sm (3), Ce (4), Gd (5); n = 3 or 4) which exhibit an unusual non-interpenetrated (10,3)-d (or utp net) topology. The photophysical properties of these lanthanide MOFs have been assessed, in which the Tb³⁺ complex 2 displays bright green luminescence with quite high efficiency (Φ_overall = 50%) and a long excited state lifetime (τ_obs = 1.1 ms).