Luminescent metal organic frameworks for sensing and gas adsorption studies

Abstract

Two three-dimensional metal organic frameworks (MOFs) with a 5,5′,5′′-(2,4,6-trimethyl-1,3,5-phenylene)tris(methylene)tris(azanediyl)triisophthalic acid (H₆L) ligand, viz., {[Zn₄(L)_1/3(H₂O)₄]⁶⁺[S]}_n (LZn) and {[NaCd₂(L)(DMF)₃]⁻·(Me₂NH₂⁺)(3DMF)}_n (LCd), where the S in LZn denotes a squeezed anion and solvent molecules and DMF denotes dimethylformamide, were synthesized under solvothermal conditions. LZn is a porous compound that contains paddle wheel binuclear [Zn₂(COO)₄ and Zn₂(COO)₃] secondary building units (SBUs), while LCd is an intrapenetrating MOF with Cd₂Na trinuclear SBUs. The sensing results showed that both MOFs act as selective sensors towards nitrophenolic explosives, i.e., nitrophenol (NP), dinitrophenol (DNP), and trinitrophenol (TNP). Furthermore, LCd exhibited behavior that is typical of an ultramicroporous material and selectively adsorbed CO₂, while N₂ molecules were adsorbed only on its surface. By contrast, LZn showed selectivity towards N₂ molecules at 77 K.