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 (SA_BET) in N₂ sorption studies. The sensing result shows that 5 act as selective sensors towards TNP with quenching efficiency greater than 99%.

Keywords:

• X-ray Structure
• bicapped trigonal prismatic geometry
• gas adsorption study
• fluorescence properties

Authors’ contribution

U. P. S supervised, conceived the experiments and studies. P. V. investigated, conceptualized, synthesized and characterized the MOFs. T. V. performed the luminescence study. R. J. B. solved single crystal X-ray data. P. M. executed the gas adsorption studies. P. V. and U. P. S. wrote the paper with contributions from all authors.

Accession codes

CCDC 2061097-2061101 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; Fax: [phone].

Disclosure statement

There are no conflicts of interest to declare.

Additional information

Funding

The authors are grateful to the BRNS (DAE), Mumbai, India for financial assistance. P. Verma gratefully acknowledges IIT Roorkee for awarding MHRD fellowship. The grant code is 37018.