Structure and Properties of 1,3-Phenylenediboronic Acid: Combined Experimental and Theoretical Investigations

A Crystalline Dimeric Steroidal Diboronate with Electronically Impeded Rotation

The dimeric steroid SMR-3, featuring a 1,4-phenyldiboronic ester flanked by two pregnan-triol frameworks, was synthesized to explore the intramolecular dynamics of its central component. The structural data from single-crystal X-ray diffraction studies and the Hirshfeld analyses indicate small steric effects around the aromatic ring that should favor the intended motion. However, solid-state NMR data obtained through VT ¹³C{¹H} CPMAS and ²H spin-echo experiments, using the deuterated analogue SMR-3D₄, revealed that this component is rigid even at temperatures where other reported steroidal molecular rotors experience fast rotation (85 °C). A combination of classical molecular dynamics, molecular mechanics, and correlated ab initio calculations allowed us to distinguish the steric and electronic factors that restrict the potential motion in this compound. The experimental and computational data reveal that electronic components dominate the behavior and are responsible for the high rotational barrier in the SMR-3 crystal.

Heteroelement Analogues of Benzoxaborole and Related Ring Expanded Systems

The review covers the chemistry of organoboron heterocycles structurally related to benzoxaboroles where one of the carbon atoms in a boracycle or a fused benzene ring is replaced by a heteroelement such as boron, silicon, tin, nitrogen, phosphorus, or iodine. Related ring expanded systems including those based on naphthalene and biphenyl cores are also described. The information on synthetic methodology as well as the basic structural and physicochemical characteristics of these emerging heterocycles is complemented by a presentation of their potential applications in organic synthesis and medicinal chemistry, the latter aspect being mostly focused on the promising antimicrobial activity of selected compounds.

Design of solvatomorphic structures based on a polyboronated tetraphenyladamantane molecular tecton

A series of solvatomorphic structures of tetrakis(4-dihydroxyborylphenyl)adamantane were investigated.

Covalent organic frameworks from a monomer with reduced symmetry: polymorphism and Sierpiński triangles

We report on the synthesis of a covalent organic framework based on the low-symmetry 1,3-benzenediboronic acid precursor. Two distinct polymorphs are obtained, a honeycomb network and Sierpiński triangles, as elucidated by scanning tunneling microscopy. Control over polymorph formation was achieved by varying the precursor concentration for on-surface synthesis.

Analysis of solvent-accessible voids and proton-coupled electron transfer of 2,6-bis(1H-imidazol-2-yl)pyridine and its hydrochloride

The crystal structures of the solid form of solvated 2,6-bis(1H-imidazol-2-yl)pyridine (H₂dimpy) trihydrate, C₁₁H₉N₅·3H₂O·[+solvent], I, and its hydrate hydrochloride salt 2-[6-(1H-imidazol-2-yl)pyridin-2-yl]-1H-imidazol-3-ium chloride trihydrate, C₁₁H₁₀N₅⁺·Cl^-·3H₂O, II, are reported and analysed in detail, along with potentiometric and spectrophotometric titrations for evaluation of the acid-base equilibria and proton-coupled electron-transfer reactions. Compound I crystallizes in the high-symmetry trigonal space group P3₂21 with an atypical formation of solvent-accessible voids, as a consequence of the 3₂ screw axis in the crystallographic c-axis direction, which are probably occupied by uncharacterized disordered solvent molecules. Additionally, the trihydrated chloride salt crystallizes in the conventional monoclinic space group P2₁/c without the formation of solvent-accessible voids. The acid-base equilibria of H₂dimpy were studied by potentiometric and spectrophotometric titrations, and the results suggest the formation of H₃dimpy⁺ (pK_a1 = 5.40) and H₄dimpy²⁺ (pK_a2 = 3.98), with the electrochemical behaviour of these species showing two consecutive irreversible proton-coupled electron-transfer reactions. Density functional theory (DFT) calculations corroborate the interpretation of the experimental results and support the assignment of the electrochemical behaviour.