5-Arylidene derivatives of Meldrum’s acid: Synthesis, structural characterization using single crystal and powder crystal X-ray diffraction, and electronic properties

• Crystal structures of 5-arylidene derivatives of Meldrum’s acid.
• Structure determination from X-ray powder diffraction.
• Comparison of intermolecular interaction via Hirshfeld surface analysis.
• Electronic structure evaluation with DFT calculations.

Four 5-arylidene derivatives of Meldrum’s acid, 5-(4-chlorobenzylidene)-2,2-dimethyl-1,3-dioxane-4,6-dione (2), 5-(3-hydroxybenzylidene)-2,2-dimethyl-1,3-dioxane-4,6-dione (3), 5-(3,4-dimethoxybenzylidene)-2,2-dimethyl-1,3-dioxane-4,6-dione (4) and 5-(2,4-dimethoxy benzylidene)-2,2-dimethyl-1,3-dioxane-4,6-dione (5) have been synthesized and their crystal structures have been determined using single crystal X-ray diffractometry for 2, 4 and 5 and X-ray powder diffraction for 3. The nature of intermolecular interactions in 2–5 has been analyzed through Hirshfeld surfaces and 2D fingerprint plots. The DFT optimized molecular geometries in 2–5 agree closely with those obtained from the crystallographic studies. The crystal packing in 2–5 exhibits an interplay of OH⋯O, CH⋯O, CH⋯Cl and CH⋯π (arene) hydrogen bonds and π⋯π interactions, which assemble molecules into three-dimensional architecture in 2, 3 and 5 and two-dimensional framework in 4. The Hirshfeld surface analyses of 2–5, Meldrum’s acid (1) and a few related 5-arylidene derivatives of Meldrum’s acid retrieved from the Cambridge Structural Database (CSD) indicate that about 85% of the Hirshfeld surface area (72% in 2 where H⋯Cl contribution is about 13%) in this class of compounds are due to H⋯H, O⋯H and C⋯H contacts. The HOMO–LUMO energy gap (>2.2 eV) in 2–5 indicates a significant degree of internal charge transfer within the molecule.

Four 5-arylidene derivatives of Meldrum’s acid have been synthesized, structurally characterized using single crystal and powder crystal X-ray diffraction and their intermolecular interactions are compared via Hirshfeld surface analysis. The electronic structures have been evaluated via DFT calculations.Figure optionsDownload as PowerPoint slide