Unifying the <b>pts</b> and <b>sql</b> Isomers of the Lanthanide-<i>p</i>ETTC Metal–Organic Frameworks

Luminescent metal–organic frameworks (LMOFs) are tunable solid-state functional materials that can be customized to possess desirable optical properties. Tetraphenylethene-based ligands (such as para-H4ETTC, 4′,4‴,4‴′,4″′′′′′-(ethene-1,1,2,2-tetrayl)tetrakis([1,1′-biphenyl]-4-carboxylic acid)) are particularly useful for such materials, as they are both chemically and structurally robust as well as highly emissive in the solid state. Despite the value and interest in lanthanide-based LMOFs, relatively few studies have been performed on the lanthanide-pETTC system, though literature describes two isomeric phases of distinct topology–the three-dimensional pts net and the 2D → 3D inclined sql net. Here, in order to define the relationship of these two phases to each other and to potentially investigate new phases, the full lanthanide series (excluding Pm) is combined with the p-H4ETTC ligand using reported synthetic protocols. Only the sql isomer is found under all synthetic conditions, yielding an isostructural sql series of anionic Ln-pETTC MOFs with the formula [Ln(ETTC)(H2O)2][NH2(CH3)2]. Additionally, in the smallest lanthanide ions (Yb and Lu), a similar but charge-neutral sql phase has been uncovered with the formula Ln(HETTC)(H2O)2. The crystallographic structures and bulk luminescent properties of these materials are described, and a hypothesis for the synthesis-dependent anionic vs neutral phase distribution is presented. This work unifies the Ln-pETTC system into one cohesive sql series and endeavors to aid future study and application of these robust solid-state emitters.