Halogen bonding in cadmium(II) MOFs: its influence on the structure and on the nitroaldol reaction in aqueous medium

A solvothermal reaction of Cd(II) with the dicarboxyl-functionalized arylhydrazone pro-ligands, 5-(2-(2,4,6-trioxotetrahydro-pyrimidin-5(2H)-ylidene)hydrazineyl)isophthalic acid (H₅L¹) and 5-(2-(2,4-dioxopentan-3-ylidene)hydrazineyl)isophthalic acid (H₃L²), or their halogen bond donor centre(s) decorated analogs 2,4,6-triiodo-5-(2-(2,4,6-trioxotetrahydropyrimidin-5(2H)-ylidene)hydrazineyl)isophthalic acid (H₅L³) and 5-(2-(2,4-dioxopentan-3-ylidene)hydrazineyl)-2,4,6-triiodoisophthalic acid (H₃L⁴), leads to the formation of known [Cd(H₃L¹)(H₂O)₂]_n (1) and new {[Cd(HL²)(H₂O)₂(DMF)]·H₂O}_n (2), [Cd(H₃L³)]_n (3) and {[Cd₂(μ-H₂O)₂(μ-H₂L⁴)₂(H₂L⁴)₂]·2H₂O}_n (4) coordination compounds, respectively. The aggregation of mononuclear units via Cd-OC and Cd-OH₂ coordination and C_Ar-I⋯I types of intramolecular halogen bonds lead to a dinuclear tecton 4. Both C_Ar-I⋯O and C_Ar-I⋯I types of intermolecular halogen bonds play a fundamental role in the supramolecular architectures of the obtained metal-organic frameworks 3 and 4. Theoretical (DFT) calculations confirmed the presence of the C_Ar-I⋯O and C_Ar-I⋯I halogen bonds in 3 and 4 and allowed their characterisation. The formation of intermolecular noncovalent interactions between the attached iodine substituents to the hydrazone ligands and polar solvent (water or methanol) molecules promoted, at least in part, the solubility of the corresponding complexes (3 and 4), which act as homogeneous catalyst precursors in the Henry reaction between aldehydes and nitroethane. The corresponding β-nitroalkanol products were obtained in good yields (66-79%) and with good diastereoselectivity (threo/erythro ca. 72 : 28) in water at room temperature.

The Solid State Landscape of the Sildenafil Drug

Sildenafil, the active ingredient of the drug developed by Pfizer for the treatment of erectile dysfunction was firstly synthesized in 1989 in the United Kingdom and since then it has become one of the most prescribed drugs for sexual performance in the western world with more than 2.7 million prescriptions in the US in 2021. Since its discovery, this drug compound has attracted the interest of formulators and crystallographers, with a high number of crystal forms of sildenafil being found and characterized, including polymorphs, hydrates, solvates, salts and cocrystals, converting it in one of the most promiscuous multicomponent crystal former drugs in the pharmaceutical sciences arena. In this minireview, the polymorph, pseudopolymorph and multicomponent solid forms landscape of sildenafil is presented through a comprehensive compilation of their 42 solid forms reported in literature.

Sildenafil–Resorcinol Cocrystal: XRPD Structure and DFT Calculations

Herein, the X-ray powder diffraction (XRPD) crystal structure of a new Sildenafil cocrystal is reported, where resorcinol has been used as the coformer. The crystal structure has been solved by means of direct space methods used in combination with density functional theory (DFT) calculations. In the structure, the Sildenafil and resorcinol molecules form cooperative hydrogen bond (HB) and π-stacking interactions that have been analyzed using DFT calculations, the molecular electrostatic potential (MEP) surface, and noncovalent interaction plot (NCI plot). The formation of O–H⋯N H-bonds between resorcinol and Sildenafil increases the dipole moment and enhances the antiparallel π-stacking interaction.