Encapsulation of N-containing compounds in a new hydrophilic Cd-based crystalline sponge via coordinative alignment method

Abstract

The crystalline sponge method (CSM) is a technology which allows precise molecular determination of non-crystalline compounds, without the need to crystallise them independently, by soaking them in a crystalline metal–organic framework (MOF). To expand the CSM to a wider range of guest molecules, the development of a new crystalline sponge is essential. In this study a new Cd-based MOF {[Cd₇(4,4′4′′-[1,3,5-benzenetriyltris(carbonylimino)]-trisbenzoato)₄(μ₃-OH)₂(H₂O)₄(DMF)₄]·(solvent)_x}_n was synthesized and investigated as an alternative crystalline sponge (2). Sponge 2 demonstrated versatility in solvent stability compared to the well-studied [{(ZnI₂)₃(tris(4-pyridyl)-1,3,5-triazine)₂·x(CHCl₃)}_n] (1) and was stable in the presence of polar aprotic, polar protic solvents and Lewis bases. Inclusion complexes with three solvents, acetonitrile, acetone, and isopropanol were prepared. These guest molecules were fixed in the pore via hydrogen bonding confirming the hydrophilic pore environment of sponge 2. Notably, sponge 2 also demonstrated the ability to accommodate N-containing compounds such as pyridine, 3,5-lutidine, and 4-aminopyridine via the coordinative alignment method (CAL). A study was conducted to compare the ability of sponge 2 and related pyridine containing sponge 3 by encapsulating the same pair of guests: N,N-dimethylaniline and propiophenone.