Structural and Energetic Landscape of Fluorinated 1,4-Phenylenediboronic Acids

Abstract

The results of X-ray crystallographic and computational studies of a series of fluorinated 1,4-phenylenediboronic acids (i.e., fluoro-1,4-phenylenediboronic acid, 2,6-difluoro-1,4-phenylenediboronic acid, 2,3-difluoro-1,4-phenylenediboronic acid, 2,5-difluoro-1,4-phenylenediboronic acid, and tetrafluoro-1,4-phenylenediboronic acid) are reported. The effect of fluorine substitution on crystal organization in the presence of strong and directional hydrogen bonds was studied. Comparison with the two previously reported forms of the unsubstituted 1,4-phenylenediboronic acid revealed a strong relation between a supramolecular network and the number of water molecules present in the crystal lattice. As indicated by the theoretical calculations performed in the CRYSTAL and PIXEL programs, the structures with greater amount of water are better stabilized (from about −170 kJ·mol–1 for anhydrous forms to about −420 kJ·mol–1 for tetrahydrate). The energy of hydrogen bonded dimers vary from −40 kJ·mol–1 to −50 kJ·mol–1. Contacts with fluorine atoms play rather a secondary role in the crystal packing. Fluorine substituents tend to interact with the electropositive boron atom. Furthermore, intramolecular interactions significantly affect the torsion angle of the B­(OH)2 group. The constrained energy scan revealed that stronger interactions with substituents stabilize the planar conformation and hamper the rotation of the boronic group. This in turn has a further impact on the interactions within selected crystal motifs and supposedly rules the proton disorder within boronic fragments. Besides the interactions with the fluorine atoms, other weak contacts such as C­(π)···B and O···B also influence the molecular organization. The energy of the corresponding dimers varies from −15 kJ·mol–1 to −25 kJ·mol–1.

Synthesis, structural characterization and computational studies of catena-poly[chlorido[μ3-(pyridin-1-ium-3-yl)phosphonato-κ3 O:O′:O′′]zinc(II)]

“…4. The total energy falling on the ASUequivalent fragment of a polymeric chain in the crystal structure of (1) is À205.4 kJ mol À1 and is comparable with the cohesive energy values for molecular crystals of small organic species interacting via hydrogen bonds further stabilized by stacking interactions (Durka et al, 2012;Jarzembska et al, 2013;Kutyła et al, 2016;Price, 2014). N1-H1NÁ Á ÁO33 iii and C6-H6Á Á ÁO31 iv , as well as offset faceto-facestacking interactions.…”

“…A similar procedure to that mentioned above was used by Durka et al (2012). A supermolecular approach was employed to derive the interaction energy values.…”

A Surprising Substituent Effect Provides a Superior Boronic Acid Catalyst for Mild and Metal‐Free Direct Friedel–Crafts Alkylations and Prenylations of Neutral Arenes

“…Another possibility to explain the surprising superiority of 1 b focuses on the effect of the ortho substituents on the stability of the transition state for hydroxyl activation (Scheme ). Regardless of boron’s ionization state (trigonal neutral or tetrahedral boronate), polarization and breakage of the CO bond may be facilitated by a weak CH⋅⋅⋅OB hydrogen bond (transition structure A ) 21. Alternatively, lone‐pair repulsions in B may increase the activation energy for CO bond ionization when using catalyst 1 a .…”

Synthesis, XRD Studies and NLO Properties of [p-H2NC6H4CH2NH3][B5O6(OH)4]·1/2H2O and NLO Properties of Some Related Pentaborate(1−) Salts

“…The a-interactions with neighbours are paired e.g. O10H10ÁÁÁO11 and O17H17ÁÁÁO6 resulting in energetically favourable [13,30] eight membered rings, R 2 2 (8) [31] (Fig. 4).…”