Supramolecular assemblies in the molecular complexes of 4-cyanophenylboronic acid with different N-donor ligands

Molecular complexes of 4-cyanophenylboronic acid (CB) with various N-donor compounds having different conformational features, for example, rigid (1,10-phenanthroline (110phen), 4,7-phenanthroline (47phen), 1,7-phenanthroline (17phen) and acridine (acr)) and linear (1,2-bis(4-pyridyl)ethane (bpyea), 1,2-bis(4-pyridyl)ethene (bpyee) and 4,4'-azopyridine (azopy)), have been reported. In all complexes, the -B(OH)2 moiety is found to be in a syn-anti confirmation, with the exception of structures containing 110phen, bpyee, and azopy, wherein, syn-syn conformation is observed. Further, CB molecules remain intact in all structures except in the complexes with some linear N-donor ligands, wherein -B(OH)2 transforms to monoester (-B(OH)(OCH3)) prior to the formation of corresponding molecular complexes. In such boronic monoester complexes, the conformation of -B(OH)(OCH3) is syn-anti with respect to the -OH and -OCH3 groups. Also, complexes mediated by azopy and bpyee exist in both hydrated and anhydrous forms. In these anhydrous structures, the recognition pattern is through homomeric (juxtaposed -CN and -B(OH)2) as well as heteromeric (between hetero N-atom and -B(OH)2) O-H⋯N hydrogen bonds, while only heteromeric O-H⋯N hydrogen bonds hold co-formers in all other structures. Depending upon the conformational features of both co-formers, molecules are packed in crystal lattices in the form of stacked layers, helical chains, and crossed ribbons. All structures are fully characterized by single-crystal X-ray diffraction and phase purity is established by powder X-ray diffraction. Additionally, correlation among structures is explained by calculating a similarity index and performing a Hirshfeld surface analysis to quantify the strength and effectiveness of different types of intermolecular bonds that stabilize these structures along with the presentation of energy frameworks, representing the strength of the interactions in the form gradient cylinders. Also, the morphology of each complex was computed by BFDH methodology to correlate with the actual crystal morphology and packing arrangement.

Four-Coordinate Monoboron Complexes with 8-Hydroxyquinolin-5-Sulfonate: Synthesis, Crystal Structures, Theoretical Studies, and Luminescence Properties

8-Hydroxyquinolin-5-sulfonic acid (8HQSA) was combined with 3-pyridineboronic acid (3PBA) or 4-pyridineboronic acid (4PBA) to give two zwitterionic monoboron complexes in crystalline form. The compounds were characterized by elemental analysis, single-crystal X-ray diffraction studies, and IR, 1H NMR, UV-Visible, and luminescence spectroscopy. The analyses revealed compounds with boron atoms adopting tetrahedral geometry. In the solid state, the molecular components are linked by charge-assisted (B)(O-H···−O(S) and N+-H···O(S) hydrogen bonds aside from C-H···O contacts and π···π interactions, as shown by Hirshfeld surface analyses and 2D fingerprint plots. The luminescence properties were characterized in terms of the emission behavior in solution and the solid state, showing emission in the bluish-green region in solution and large positive solvatofluorochromism, caused by intramolecular charge transfer. According to TD-DFT calculations at the M06-2X/6-31G(d) level of theory simulating an ethanol solvent environment, the emission properties are originated from π-π * and n-π * HOMO-LUMO transitions.

New Co-Crystals/Salts of Gallic Acid and Substituted Pyridines: An Effect of Ortho-Substituents on the Formation of an Acid–Pyridine Heterosynthon

Co-crystallization of gallic acid with pyridines and their polyaromatic analogue, quinoline, ortho-substituted by various proton-donating groups able to form hydrogen bonds, produced the only reported co-crystal of gallic acid with an ortho-substituted pyridine, 2-hydroxypyridine, as its preferred pyridone-2 tautomer, and four new crystalline products of gallic acid. These co-crystals, or gallate salts depending on the choice of the pyridine-containing compound, as predicted by the pKa rule, were identified by X-ray diffraction to feature the popular acid–pyridine heterosynthon found in most of the two-component systems of gallic acid that lack ortho-substituents in the pyridine-containing compound. This single-point heterosynthon is, however, modified by one or two proton-donating ortho-substituents, which sometimes may transform into the proton acceptors in an adopted tautomer or zwitterion, to produce its two- or other multi-point variants, including a very rare four-point heterosynthon. The hydrogen bonds they form with the gallic acid species in the appropriate co-crystals/salts strongly favors the formation of the acid–pyridine heterosynthon over the acid–acid homosynthon. In the competitive conditions of multi-component systems, such a modification might be used to reduce supramolecular-synthon-based polymorphism to produce new pharmaceuticals and other crystalline materials with designed properties.

Supramolecular networks and Hirshfeld surfaces of oxydiacetic acid and iminodiacetic acid salts

Oxydiacetic acid (Oda) and iminodiacetic acid (Ida) have been combined with two diamines, namely ethylenediamine (en) and o-phenylenediamine (o-phen), to give three molecular crystals of compositions [(Oda^2-)(en²⁺)]·H₂O (Odaen), [(Ida^-)(0.5en⁺)] (Idaen) and [(Oda^-)(o-phen⁺)] (Odaophen). Single crystal X-ray structure determination of the three molecular salts revealed that the hydrogen bonding interactions form distinct supramolecular chains. In Odaen, water molecules and Oda^2- anions generate one-dimensional supramolecular chains where two chains overlap each other in zigzag form. In Odaophen, Oda^- anions generate a one-dimensional linear supramolecular chain. In Idaen, both intermolecular and intramolecular proton transfer occurs. Ida^- anions generate a one-dimensional zigzag chain. These one-dimensional supramolecular chains extend to form different two-dimensional supramolecular chains by the interaction of diaminium and monoaminium cations. Intermolecular close contacts are also examined using Hirshfeld analysis to reveal similarities and differences in the crystal structures.

Supramolecular zwitterions based on a novel boronic acid–squarate dianion synthon

We report a novel heterodimeric charge-assisted hydrogen bonding synthon and prove its robustness by preparation of a three-component co-crystal.

Supramolecular Organoplatinum(IV) Chemistry: Dimers and Polymers Formed by Intermolecular Hydrogen Bonding

The reaction of [PtMe₂(6-dppd)], 1, where 6-dppd is a 1,4-bis(2-pyridyl)pyridazine derivative, with bromoalkanes BrCH₂R, having a hydrogen-bond donor group R, gave the corresponding chiral products of trans oxidative addition [PtBrMe₂(CH₂R)(6-dppd)], 2a, R = CO₂H; 3, R = 4-C₆H₄CO₂H; 4, R = 4-C₆H₄CH₂CO₂H; 7, R = 2-C₆H₄CH₂OH; 8, R = 4-C₆H₄B(OH)₂; 9, R = 3-C₆H₄B(OH)₂; and 10, R = 2-C₆H₄B(OH)₂. Complex 2a was formed in equilibrium with two isomers formed by cis oxidative addition, while the reaction of 1 with BrCH₂CH₂CO₂H gave mostly [PtBrMe(6-dppd)], 6. The supramolecular chemistry was studied by structure determination of six of the platinum(IV) complexes, with emphasis on the preference of the hydrogen bond acceptor (O, pyridyl N, or Br atom), formation of monomer, dimer, or polymer, and self-recognition or self-discrimination in self-assembly. Complex 7 formed a monomer with the OH···N hydrogen bond, and complexes 2a and 10 formed racemic dimers by complementary hydrogen bonding with self-discrimination between CO₂H or B(OH)₂ groups, respectively. Complexes 3, 4, and 9 formed polymers by intermolecular hydrogen bonding with self-recognition, with 4 containing OH···N and 3 and 9 containing OH···Br hydrogen bonds. It is concluded that there is no clear preference for the hydrogen bond acceptor group, and that the observed product depends also on the orientation of the hydrogen bond donor group.

Crystal structure and Hirshfeld surface analysis of 3-cyano-phenyl-boronic acid

In the title compound, C7H6BNO2, the mean plane of the -B(OH)2 group is twisted by 21.28 (6)° relative to the cyano-phenyl ring mean plane. In the crystal, mol-ecules are linked by O-H⋯O and O-H⋯N hydrogen bonds, forming chains propagating along the [101] direction. Offset π-π and B⋯π stacking inter-actions link the chains, forming a three-dimensional network. Hirshfeld surface analysis shows that van der Waals inter-actions constitute a further major contribution to the inter-molecular inter-actions, with H⋯H contacts accounting for 25.8% of the surface.