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A series of polyhalogenated diaminobenzonitriles and 18-crown-6 ether were used to reveal the dependence of the stoichiometry and supramolecular structure of co-crystals on various factors. 2,6-Diamino-3,5-difluoro-, 2,6-diamino-4-chloro-3,5-difluoro-, and 2,6-diamino-4-chloro-3-fluorobenzonitriles, as well as 2,4-diamino-3,5-difluorobenzonitrile give 1 : 1 co-crystals regardless of the diamine : crown ratio in the crystallization solution (from 2.5 : 1 to 1 : 2.5) and the nature of the solvent. According to X-ray diffraction data, the supramolecular structures of these co-crystals can be considered as 1D assemblies with the only structure-forming N–H⋯Ocr hydrogen bond. 2,4-Diamino-3,5,6-triflurobenzonitrile forms no 1 : 1 co-crystal, but yields co-crystals of 4 : 3 (under most of the studied conditions) and 2 : 1 (in CCl4 solution) stoichiometry. The N–H⋯NC hydrogen bond and p⋯π electron interactions, along with the N–H⋯Ocr H-bond, participate in the formation of the 3D supramolecular structures of these co-crystals. The effect of the number of F atoms on the co-crystallization behaviour of difluoro- and trifluoro-2,4-diaminobenzonitriles was rationalized using quantum-chemical computations of the interaction energies of N–H⋯NC bonded pairs of these diamines in the experimental crystals and DFT simulated models. The DSC curves of each co-crystal contain a single peak corresponding to a crystal-to-liquid phase transition (melting), which does not change in melting–crystallization cycles, indicating that the stoichiometry and crystal structure are reproducible. [ABSTRACT FROM AUTHOR]

Luminescent properties of needle‐like single crystal diamonds are investigated in a wide range of wavelength. The luminescent spectra with zero phonon lines centered at 389, 442, 468, 534, 563, 575, and 738 nm are detected using excitation by photons and electrons. Obtained photo‐ and cathodo‐luminescent (PL and CL) spectra indicate presence in the single‐crystal diamond needles of nitrogen‐ and silicon‐vacancy centers as well as substitutional or/and interstitials related to these atomic impurities. The dependencies of PL intensities of the 575 and 738 nm lines (related, correspondingly, to nitrogen‐ and silicon‐vacancy centers) on excitation wavelength are determined. Time‐resolved measurements are performed for the 575 nm PL line. The luminescence decay behavior for this line demonstrates the presence of recombination processes with characteristic times of about 28 ns (on 200 ns time scale) and 2.8 ns (on 20 ns time scale). [ABSTRACT FROM AUTHOR]