An isostructural series of metal-organic frameworks: selective gas adsorption and sensing studies

Abstract

The solvothermal reaction of Ln(NO3)3•6H2O (Ln = Nd, Sm, Eu, Tb, and Dy) with 9,10-bis(4-carboxylatopyridinium-1-methylene)anthracene dibromide (H2L)Br2 resulted in the formation of an isostructural series of lanthanide-based metal organic frameworks (Ln-MOFs), {[Nd(L)3/2(H2O)2]·(NO3)3·(S)}n (1), {[Sm(L)3/2(H2O)2]·(NO3)3·(S)}n (2), {[Eu(L)3/2(H2O)2]·(NO3)3·(S)}n (3), {[Tb(L)3/2(H2O)2]·(NO3)3·(S)}n (4) and {[Dy(L)3/2(H2O)2]·(NO3)3·(S)}n (5), where S denotes squeezed disordered solvent molecules and out of three nitrate ions in the voids, one nitrate is squeezed due to the high disorder. These MOFs were characterized with various techniques and single crystal X-ray analysis revealed a three dimensional (3D) (4,4,6)-connected metal organic framework with mononuclear metallic nodes in bicapped trigonal prismatic geometry. From the present series, we selected {[Sm(L)3/2(H2O)2]·(NO3)3·(S)}n (2) as a representative example for structural description and gas adsorption study whereas {[Dy(L)3/2(H2O)2]·(NO3)3·(S)}n (5) was used for the sensing of nitro compounds. All MOFs showed stability up to 200 °C. 2 demonstrates a higher CO2 uptake, despite exhibiting a low specific surface area (SABET) in N2 sorption studies. The sensing result shows that 5 act as selective sensors towards TNP with quenching efficiency greater than 99%.