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The cetylpyridinium (CP) dipicrylamide (DPA) ion pair has been synthesized and characterized by the FT-IR and NMR (1H and 13C) spectroscopy, theoretically studied and tested as ion-exchanger for cetylpyridinium selective electrodes. The molecular dynamics and further DFT optimization indicate face-to-face π-π stacking interaction between pyridinium and 2,4,6-trinitrophenyl rings. The presence of weak interactions between hydrogens of cetyl chain and oxygens of nitro groups of DPA anion was confirmed by RDG function analysis. Numeric reactivity descriptors computed at the B3LYP/6-31+G(d,p) level of theory show that CP-DPA has electrophilic character and can readily react with bases. Two fabricated electrodes with the CP-DPA ion-exchanger showed near-Nernstian responses towards CP chloride in the concentration range from 1 × 10−2 to 1 × 10−5 mol/L. In the case where dibutyl phthalate was used as plasticizer, the slope equals 57.2 ± 1.3 mV/decade, whereas for the case of dioctyl phthalate the slope is 61.6 ± 1.2 mV/decade.

The structure of a newly synthesized 3-methylthio-4-phenyl-5-phenylamino-1,2,4-triazole 1 and its hexabromotellurate salt 2 was investigated. The X-ray diffraction study of 2 gives the insight on the different interaction types in the crystal. The DFT calculations were used for the comprehensive study of the intramolecular and intermolecular forces that are present in the title 3-methylthio-4-phenyl-5-phenylamino-1,2,4-triazole hexabromotellurate. The presence of three different aromatic moieties in the investigated compounds cause π-π stacking interactions which were studied through the Hirshfeld surface analysis and with the discrimination of weak interaction types by filling color to a reduced density gradient (RDG) function isosurface. The RDG in the crystalline state was calculated upon experimental molecular geometry by partitions of the crystal to QM part that was calculated at M06-L/6-311G(d,p) level, and the semi-empirical QM part that was modeled with the PM7 method in QM/MM-like manner. The reactivity of 3-methylthio-4-phenyl-5-phenylamino-1,2,4-triazole and its protonated form was also discussed in terms of conceptual DFT theory and it shows the tendency of sulfur to be the most active center in an electrophilic and radical attack, whereas the site for nucleophilic substitution is medium dependent and not an unequivocal. NICS(1) index was used for the analysis of aromaticity of three different cyclic moieties. The present study insights the changes in the structure of a polyfunctional substituted triazole upon its protonation and explains these changes with the analysis of weak interactions.

The synthesis of a new hexabromotellurate of triazole ring-containing amino acid is described. XRD, NMR and DFT analysis of the structure of protonated [(5-amino-4-phenyl-4H-1,2,4-triazol-3-yl)sulfanyl]acetic acid testifies the protonation of the first nitrogen atom of the triazole ring. Hirshfeld surface analysis identifies numerous intermolecular interactions in the newly synthesized organic-inorganic hybrid hexabromotellurate. The DFT based comprehensive analysis of the structures of possible conformers also testifies the higher thermodynamic stability of the 1-protonated triazole cation, whereas the starting [(5-amino-4-phenyl-4H-1,2,4-triazol-3-yl)sulfanyl]acetic acid exists in solution in neutral form with the intermolecular hydrogen bond between the carboxylic acid OH group and the second nitrogen of the triazole ring. The experimentally observed NMR upfield shift of the signal of the exocyclic amino group was studied via GIAO computations and was explained through the analysis of the HOMOs of the neutral and protonated forms of the triazole compound.

A new cetylpyridinium picrate ionic liquid has been synthesized and characterized by differential thermal analysis, XRD, FT-IR, and NMR (1H and 13C) spectroscopy. Differential thermal analysis indicates the congruent melting of cetylpyridinium picrate and a temperature range of liquid state is 47–267 °C. A solid form of the sample characterized with a polymorphic transformation at 37 °C, which was confirmed via the XRD analysis. The interionic charge-transfer interactions, namely the charge transfer from the picrate anion to the cetylpyridinium cation, were detected by comparison of NMR spectra of DMSO solutions of the ionic liquid and cetylpyridinium chloride. The H–NMR chemical shifts’ differences of about 0.2 ppm and 0.1 ppm were observed in the case of the o-protons and the α-methylene group protons, respectively. Additionally, the charge-transfering between the attracted ions was confirmed by DFT calculations. Based on the solid state NMR technique, the higher ions mobility was suggested for the solid sample of the ionic liquid in comparison to the solid cetylpyridinium chloride monohydrate. Moreover, the association constants KA at 22, 30, 40, and 50 °C, obtained from the electrical conductivity measurements, clearly testifies much lower dissociation in the case of picrate. The KA values of cetylpyridinium picrate and chloride in DMSO medium at 22 °C equal 748.7 L/mol and 525.0 L/mol, respectively. The performed DFT computations of the reduced density gradient function in four proposed structures of the new ionic liquid cation-anion pair identifies the presence of weak non-covalent C H•••O N interactions between cetyl chain hydrogen atoms and nitro groups of picrate was explored through DFT calculations and analysis of the RDG function.