Tuning the formation of MOFs by pH influence: X-ray structural variations and Hirshfeld surface analyses of 2-amino-5-nitropyridine with cadmium chloride

Abstract

Self-assembly through tuning the N-donor ligand and coordinative preferences of Cd(II) ions, two metal–organic frameworks, namely {[Cd(L1)₂(Cl)₂]_n·H₂O} (1) and {[CdCl₃]⁻·[H(L1)]⁺}_n (2) where, (L1) = 2-amino-5-nitropyridine, have been synthesized at different pH values under hydrothermal conditions and characterized by single crystal X-ray diffraction analyses. The structural diversities of both the complexes reveal that the pH value of the reaction system plays a crucial role in the assembly of metal–organic frameworks (MOFs). The X-ray single crystal diffractions show that the formed two complexes reveal a diversified structure with novel layer architecture. As anticipated, both complexes are interlinked through hydrogen bonding interactions affording supramolecular frameworks, but surprisingly, complex 2 exhibit both anion⋯π and lone-pair⋯π interactions in the solid-state assembly. Intricate combinations of anion⋯π/π⋯lone-pair interactions lead to the remarkable unusual supramolecular framework in 2. Investigation of Hirshfeld surface analysis reveals a much more detailed scrutiny of intermolecular interactions experienced by each complex. The Hirshfeld surface analysis was successfully deployed here to visualize and elaborate the similarities and differences in the molecular environments of the two complexes.