Series of Lanthanide-Alkali Metal-Organic Frameworks Exhibiting Luminescence and Permanent Microporosity

Abstract

A series of permanently porous luminescent lanthanide frameworks of the general formula, [Na6(H2O)6][Ln(L)4](H2O)nCl, Ln = Sm (1), Eu (2), Gd (3), Tb (4), and Dy (5), have been prepared by the reaction of trivalent lanthanide salts with sodium-4,4‘-disulfo-2,2‘-bipyridine-N,N‘-dioxide, L. The structures are formed via the one-pot self-assembly of the anionic cubic metalloligand, [Ln(L)4]5-, and subsequent cross-linking with sodium cations and chloride to afford a three-dimensional network with two-dimensional channels. The cross-linking units involve [Na4Cl]3+ clusters which resemble ideal faces of the halite structure. Both coordinated and uncoordinated water molecules, up to ∼80%, can be reversibly removed from 1−5 as identified using thermal gravimetric analysis/differential scanning calorimetry (TGA/DSC) leaving a rigid and porous framework with a Dubinin−Radushkevich (DR) surface area of 426 m2/g determined using CO2 adsorption. The permanent microporosity of the framework is also supported by the energy level splitting in the luminescence spectra which are maintained in both the hydrated and mostly dehydrated frameworks. Compounds 1−5 were each characterized by X-ray crystallography, TGA/DSC, water and CO2 sorption analyses, and luminescence spectroscopy.