Moisture-induced single-crystal-to-powder structural transformation in cadmium coordination compounds containing an electron-deficient ligand: coordinated solvent exchange and retention of dimension

Abstract

Two cadmium coordination compounds and one cadmium coordination polymer containing the electron-deficient 3,6-bis(pyridin-3-yl)-1,2,4,5-tetrazine (3,3′-pytz) ligand, namely, [Cd(3,3′-pytz)₂(EtOH)₂(ClO₄)₂] (1), [Cd(3,3′-pytz)₂(H₂O)₂(ClO₄)₂] (2) and {[Cd(3,3′-pytz)(EtOH)₂(ClO₄)₂](1,4-dioxane)}_n (3), respectively, have been successfully synthesized using the solvent effect in a solvent diffusion method. The single-crystal X-ray diffraction (SC-XRD) analysis of compounds 1 and 2 reveals the formation of zero-dimensional coordination compounds, whereas compound 3 represents a 1D linear chain coordination polymer. Further investigation shows that by the absorption of moisture from the air, while maintaining their structural dimensions, compounds 1 and 3 underwent single-crystal-to-powder structural transformation to compounds 2 and [Cd(3,3′-pytz)(H₂O)₂(ClO₄)₂]_n (3T) (B. Ebrahimi, B. Notash, T. Matar and R. Dinnebier, Inorg. Chem., 2024, 63, 983–999), respectively. Our finding was confirmed through powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), elemental analysis and FT-IR studies. Moreover, Hirshfeld surface analysis was used for a detailed investigation of the intermolecular interactions, especially semilocalized (η²) and delocalized (η⁶) anion–π interactions formed between the electron-deficient tetrazine rings and perchlorate anions in compounds 1–3. We observed several combined supramolecular synthons, such as anion–π–π–anion (ClO₄⁻⋯π_tet⋯π_tet⋯ClO₄⁻) and π–sandwich anion–π–anion (ClO₄⁻⋯π_tet⋯ClO₄⁻), in these structures.