3-Quinoline-and 5-isoquinolineboronic acids (3QBA and 5IQBA) were combined with 1-naphthyl and diphenyl phosphate (1NP and DPP) to give three crystalline molecular salts of 1:1 stoichiometric composition, viz., 3QBA-1NP, 5IQBA-1NP and 3QBA-DPP. The products were characterized by elemental analysis, single-crystal X-ray diffraction studies, IR spectroscopy, luminescence spectroscopy and TG-DSC measurements. The analysis of the solid-state structures revealed that the molecular components are linked by strong charge-assisted hydrogen bonds forming heterodimeric synthons of the type B(OH) 2 ··· -O 2 P and N + -H···O(P). In addition, the hydrogen phos- [a] Crystalline solids of compounds 3QBA-1NP, 5IQBA-1NP and 3QBA-DPP were isolated upon combination of the starting reagents in absolute ethanol. The products were characterized by elemental analysis, single-crystal X-ray diffraction (SCXRD) analysis, IR spectroscopy and TG-DSC analysis. In addition, the luminescence properties were explored. 2708 Scheme 1. List of compounds employed for the formation of the molecular salts described in this contribution.

In the title boronic acid derivative, the mean plane of the –B(OH)2 group is twisted by 21.28 (6)° relative to the cyano­phenyl ring mean plane. In the crystal, mol­ecules are linked by O—H⋯O and O—H⋯N hydrogen bonds, forming chains propagating along [101].

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.

Boronic esters are useful building blocks for crystal engineering and the generation of supramolecular architectures, including macrocycles, cages and polymers (one-, two-and three-dimensional), with potential utility in diverse fields such as separation, storage and luminescent materials. The novel dinuclear cyanophenylboronic ester described herein, namely 4,4 0 -(2,4,8,10-tetraoxa-3,9diboraspiro[5.5]undecane-3,9-diyl)dibenzonitrile, C 19 H 16 B 2 N 2 O 4 , was prepared by condensation of 4-cyanophenylboronic acid and pentaerythritol and fully characterized by elemental analysis, IR and NMR ( 1 H and 11 B) spectroscopy, single-crystal X-ray diffraction analysis and TG-DSC (thermogravimetrydifferential scanning calorimetry) studies. In addition, the photophysical properties were examined in solution and in the solid state by UV-Vis and fluorescence spectroscopies. Density functional theory (DFT) calculations with ethanol as solvent reproduced reasonably well the HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) of the title compound. Hirshfeld surface and fingerprint plot analyses are presented to illustrate the supramolecular connectivity in the solid state.