Exploring the host–guest interactions of small molecules in UoC-9(Ca)†

The Ca-based fluorinated MOF, named UoC-9 (UoC = University of Cologne), was previously published, crystallising in an orthorhombic crystal system with a 2nd order phase transition (Ima2 to Pna2₁) between room temperature and 100 K. Herein, this MOF was used as a crystalline sponge to embed a selection of six different small guest molecules inside its pores by liquid exchange. After confirming that the guest molecules were successfully loaded into the pores of UoC-9, the resulting host–guest systems were extensively analysed via single crystal X-ray diffraction. The different crystal structures allowed us to investigate the structural behaviour of UoC-9 in response to the embedded guest molecules. The lattice parameters as well as the phase transition are influenced differently by the various guests, which is described in detail by supplementary Hirshfeld surface analyses enabling us to examine the underlying host–guest interactions. The NMP@UoC-9 (NMP = N-methyl-2-pyrrolidone) system exhibits superstructure reflections with a tripled b-axis, which was also elucidated within this work.