3.4. Crystallographic Data

At 100K, crystals of 2 (C₁₅H₁₄ClN₅, M = 299.76) are orthorhombic, space group P2₁2₁2₁: a = 7.0854(3), b = 11.0430(4), c = 17.4107(7) E, V = 1362.28(9) E³, Z = 4 (Z’ = 1), d_calc = 1.462 g·cm⁻³, F(000) = 624. Intensities of 14,766 reflections were measured with a Bruker D8 Quest diffractometer equipped with the Photon III detector [λ(MoKα) = 0.71072E, щ-scans, 2θ < 61°], and 3991 independent reflections [R_int = 0.0451] were used in further refinement. The structure was solved using the direct method and refined through the full-matrix least-squares technique against F² in the anisotropic–isotropic approximation. The hydrogen atoms were found from the difference Fourier synthesis of electron density. All the hydrogen atoms were refined in the isotropic approximation without constraints imposed on the positional parameters. For 1, the refinement converged to wR2 = 0.0844 and GOF = 0.959 for all independent reflections (R1 = 0.0364 was calculated against F for 3185 observed reflections with I > 2σ(I)). All calculations were performed using the SHELX [57] and OLEX2 [58] program packages. CCDC 2,257,438 contains the supplementary crystallographic data for 1. These data can be obtained free of charge via https://www.ccdc.cam.ac.uk/structures/ (accessed on 3 July 2023) (or from the CCDC, 12 Union Road, Cambridge, CB21EZ, UK; or deposit@ccdc.cam.ac.uk). The X-ray diffraction study was performed using the equipment of the JRC PMR IGIC RAS.

The DFT calculations for the isolated cation of 1 as well for two conformations (relaxed and distorted) of the unsubstituted acridinium cation were performed using the Gaussian09 program [59]. The electronic energy calculations were performed using the def2TZVP basis set [60,61] and the PBE0 functional [62,63] with Grimme’s empirical dispersion correction [64] and Becke-Johnson damping [65]. The geometry optimization procedures were performed invoking the standard cutoff criteria and ultrafine grids. According to the normal mode calculations, both fully relaxed structures (the cation of 1 and the equilibrium unsubstituted acridinium cation) correspond to energy minima. The RDG and sign(л₂)·c^® functions were calculated using the MultiWFN program [66], whereas the topological analysis of electron density function was performed in the AIMAll program [67].