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The work is the first attempt to employ the bond valence model (BVM) in the explanation and interpretation of the phase diagrams observed for the quasibinary systems based on the ternary halides Rb3(Cs3)Sb2(Bi2)Br9(I9) (A3B2X9) and K2(Rb2,Cs2,Tl2)TeBr6(I6) (A2BX6) belonging to the structural family of perovskite. The most characteristic features of the phase diagrams of such systems are (a) a monotonic increase in the melting and crystallization temperatures when the smaller A atom is replaced by a larger chemical analogue; (b) a gradual decrease in the melting and crystallization temperatures when the bromine atoms are replaced by iodine atoms, reaching the temperature minimum at a molar ratio of ~1 : 1, and then an increase of the temperatures to the pure iodine component of the system. With the isostructurality of the starting components, in case (a) a continuous series of solid solutions (CSSS) of substitution is formed, without a temperature minimum; if the starting components belong to different structural types, then a peritectic interaction with the wide concentration limits of solid solutions is observed. Under the same conditions concerning the isostructurality/non-isostructurality of starting components, in case (b), correspondingly, either a CSSS of substitution with a temperature minimum is formed or eutectic interaction with the wide concentration limits of solid solutions is observed. Within the framework of the BVM, in case (a) a monotonic increase of the melting and crystallization temperatures when replacing a smaller atom A with a larger analogue can be interpreted as a consequence of reducing the deficit of the bond valence sum (BVS) for cations A, resulting in the stabilization of the structure as a whole. In case (b), partial replacement of one halogen ion by a halogen ions of another sort leads either to a deficit (if a larger anion is replaced by a smaller one) or to an excess (if a smaller anion is replaced by a larger one) of the BVS values for the cations A and for the anion that replaced the main halogen sort. An increase in the excess or deficit of the BVS values destabilizes the structure of ternary halides, reducing the melting and crystallization temperatures; the maximum destabilization is achieved at a ~1 : 1 molar ratio of the components, which is expressed in reaching the characteristic temperature minimum of the respective systems. The approach described in the work can expectedly be employed in explanation and interpretation of another phase diagrams based on the structures featuring the closest packing formed by alkaline metals and halogens. Keywords: ternary halides; crystal structures; phase diagrams; bond valence model.

Copper (II) orthophosphate trihydrate Cu3(PO4)2·3H2O has been synthesized by the exchange chemical reactions in aqueous solutions from the compounds Cu(NO3)2·3H2O, NH4OH and H3PO4. The final product has been investigated by using atomic absorption spectroscopy (AAS), infrared spectrometry (IRS), differential thermal analysis (DTA) and X-ray powder diffraction (XRD) techniques. For the first time, the experimental heat capacity Ср° of Cu3(PO4)2·3H2O has been investigated in the temperature range 198‒402 K. Combining the experimental results with the literature data made it possible to determine the thermodynamic and thermochemical properties, such as enthalpy НТ° , entropy SТ° , Gibbs energy GТ° , enthalpy of formation ΔHf°(T), Gibbs energy of formation ΔGf°(T) and logarithm of the equilibrium constant of formation reaction log[Kf°(T)], for the title compound. It was found that at the extreme temperatures of the experiment, Cu3(PO4)2·3H2O has Ср° = 245.96 J·mol–1·K–1, Н° = –3169.59 kJ·mol–1, S° = 311.34 J·mol–1·K–1, G° = –3231.24 kJ·mol–1 (at 198 K); Ср° = 455.31 J·mol–1·K–1, Н° = –3097.93 kJ·mol–1, S° = 551.48 J·mol–1·K–1, G° = –3319.62 kJ·mol–1, ΔHf° = –3138.48 kJ·mol–1, ΔGf° = –2625.39 kJ·mol–1, log[K ] = 341.13 (at 402 K).

The possibility of analytical determination of the uranyl cation UO22+ (taken in the form of the complex uranyl benzoate anion) by using the potentiometric titration technique has been theoretically investigated via DFT modeling and OPLS-AA force field molecular dynamics. The results of the quantum chemical calculations indicate that, among the benchmarked candidate carboxylate anions, the benzoate anion is seemingly characterized by the optimum combination of the binding properties for complexation with the uranyl cation: it shows a relatively high binding to the uranyl cation and, simultaneously, a high binding of the formed uranyl benzoate anion to the cetylpyridinium cation used as a titrant. Moreover, among the considered uranyl-carboxylate anions, the uranyl benzoate anion has been found to be the most lipophilic, which characterizes this form as the most suitable for uranyl determination.

The concept of chemical bonding is one of the key concepts in the modern chemical science. The main types of chemical bonds traditionally distinguished in the scientific literature are ionic, covalent and metallic; whereas hydrogen bonds and intermolecular interaction forces are usually taken as secondary bonds. It should be noted, however, that there are no sharp boundaries for the above types of chemical bonds. In order to predict the type of chemical bond between atomic particles, a special atomic property called the electronegativity [i.e. the ability of a given atom in a molecule to attract electron density (or valent electrons)] is widely used. The concept of electronegativity and the first scale of electronegativities of chemical elements were proposed by L. Pauling in 1932; later, several alternative scales of electronegativities were developed, including those by Mulliken and by Allred–Rochow. Using the difference between the electronegativities of atoms (DEN) and the sum of the electronegativities of atoms (SEN), one can obtain quantitative parameters which characterize the chemical bonds in specific compounds. In particular, the difference in the electronegativities of the A and B atoms characterizes the degree of ionicity for the A–B bond, while the sum of electronegativities indicates either the degree of covalency (at relatively large SEN values) or the degree of metallicity (at low SEN values). The sum of electronegativities can be replaced, if necessary, by the average electronegativity (EN av. ) of the compound. Taking the elementary substances Cs and F 2 and the binary compound CsF as reference points in the coordinates EN av. –DEN, a diagram triangle was constructed, which conveniently and clearly illustrates the type of chemical bond of different chemical compounds. The analysis of the ternary chalcogenide A I B V C VI 2 (A I – Li, Na, K, Rb, Cs; B V – As, Sb, Bi; C VI – Se, Te) compounds (which have been studied for a long time by the researchers of the Uzhhorod National University) by using the aforementioned diagram triangle in the coordinates EN av. –DEN has revealed the fact that the considered compounds are characterized by the combined (so-called "metavalent") chemical bonding recently identified in the specialized scientific literature as a separate bonding type.

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.

Сімейство потрійних галогенідів A3B2C9 (A – K, Rb, Cs; B – As, Sb, Bi; C – Cl, Br, I) класифіковано та проаналізовано на основі відповідних даних з літератури по неорганічній хімії та кристалохімії, а також на основі експериментальних результатів, одержаних в лабораторіях кафедри неорганічної хімії Ужгородського національного університету протягом останніх трьох десятиліть.Показано, що властивості вищевказаних сполук, такі як симетрія кристалів, температура плавлення Tпл. і ширина забороненої зони DE, демонструють досить сильні залежності/кореляції від величини їх середнього заряду атомних ядер Zсер.; і тому можна очікувати, що ці властивості можуть будуть ефективно передбачені для ще недосліджених сполук, що належать до тієї ж групи хімічних речовин.Хлориди вищезгаданого типу характеризуються Zсер. £ 31.0, тоді як броміди і йодиди мають значення Zсер. 31.5¸0 42.0 та 43.0¸58.0, відповідно.Встановлено, що хімічне заміщення Cl®Br®I у вищезгаданих потрійних сполуках A3B2C9 призводить до значного зменшення величини DE, тоді як заміщення As®Sb®Bi призводить до збільшення ширини забороненої зони DE для відповідних хлоридів і бромідів. Найвищі значення DE спостерігаються й очікуються для калієвих представників сполук A3B2C9; рубідієві аналоги мають дещо менші значення ширини забороненої зони, тоді як цезієві сполуки мають найменші значення DE. Очікується, що монокристали тернарних галогенідів K3(Rb3,Cs3)Bi2Cl9 з найбільш широкими забороненими зонами DE будуть придатні для використання в якості матеріалів для виготовлення широкосмугових оптичних фільтрів (від інфрачервоного до видимого діапазону спектру); декілька представників розглянутої родини A3B2C9 могли б бути використані як відрізаючі оптичні фільтри.Також було показано, що всі потрійні галогеніди вищевказаного типу A3B2C9 кристалізуються в одному з чотирьох можливих структурних аристотипів; і, як і інші розглянуті властивості, симетрія кристалів цих галогенідів залежить від значень Zсер..Підхід, що використовується в цьому дослідженні, є простим і прямолінійним, тому його можна рекомендувати для рутинних досліджень неорганічних матеріалів, що належать до одного і того ж масиву хімічно і структурно подібних сполук., The family of the ternary halides A3B2C9 (A – K, Rb, Cs; B – As, Sb, Bi; C – Cl, Br, I) have been classified and analyzed based on the relevant literature data on inorganic chemistry and crystal chemistry, and also based on the experimental results obtained in the laboratory of the Department of Inorganic Chemistry of the Uzhhorod National University over the last three decades.It was shown that the properties of the above compounds, such as crystal symmetry, melting point TM and band gap DE, demonstrate reasonably strong dependencies/correlations on their average nuclear charges Zave; so the above properties are expected to be efficiently predictable for the yet uncharacterized compounds belonging to the same family of chemicals.The chlorides the above type are characterized by Zave £ 31.0, while the bromides and iodides have the Zave values of 31.5 ¸ 42.0 and 43.0 ¸ 58.0, respectively.It has been established that the chemical substitution Cl®Br®I in the above ternary A3B2C9 compounds results in a significant decrease of the DE values, whereas the substitution As®Sb®Bi leads to an increase of the DE band gap for the relevant chlorides and bromides. The highest DE values are observed and expected for the K representatives of the A3B2C9 compounds; the Rb analogs have somewhat smaller values of band gap, while the Cs compounds have the smallest DE values. Single crystals of the K3(Rb3,Cs3)Bi2Cl9 ternary halides with the widest band gaps DE are expected to be suitable for use as the materials for manufacturing the wide-band optical filters (from infrared to visible range of the spectrum); a few representatives of the considered A3B2C9 family could be used as optical cullers.It was also shown that all ternary halides of the above A3B2C9 type crystallize in one of the four possible structural aristotype; and, as with the other considered properties, the crystal symmetry of these halides is dependent on the Zave values.The approach used in this study is simple and straightforward, so it can be recommended for routine investigations of inorganic materials belonging to the same array of chemically and structurally similar compounds.

Using multiple linear regression analysis, a simple yet efficient calculation scheme based on the Shannon effective ionic radii system has been developed for predicting the lattice parameters of the perovskite-related inorganic A2BX6 halides crystallizing in the cubic K2PtCl6 structure type.

A bactericidal and structural study on the "cetylpyridinium chloride-clinoptilolite" associates has been carried out. For the first time, the samples were synthesized using the powdered clinoptilolite from the Sokyrnytsia deposit (Transcarpathian region, Ukraine). Eight "cetylpyridinium chloride-clinoptilolite" associates have been synthesized using different cetylpyridinium chloride concentrations and further characterized by elemental analysis and FTIR techniques. The association of the cetylpyridinium cation with the zeolite anionic matrix has been studied. It was found that the adsorption of the cetylpyridinium cations occurs on the clinoptilolite surface without destroying the anionic zeolite framework. Furthermore, the antibacterial activity of the associates was analyzed, and a significant activity against Staphylococcus aureus and Candida albicans strains was observed, which is caused by the cetylpyridinium cation presence. Unmodified natural and acid-treated clinoptilolites did not show antibacterial activity; however, these can be effectively used as a matrix carrier for the cetylpyridinium cation.

Model calculations of the phonon dispersion dependencies have been carried out for the CU 7 GeSe 5 I and Ag 7 GeSe 5 I superionic crystals. For the first time, within the framework of the superspace symmetry concept the CU 7 GeSe 5 I and Ag 7 GeSe 5 I crystals have been investigated and their (3+d)-dimensional model descriptions have been developed. The description of the models of the considered structures was reduced to the construction of the modulation vectors arrays, definition of the mass modulation functions, construction of the generalized dynamic matrix as a superposition of the dynamic matrices of monoatomic structures; and the eigenvalues of the dispersion dependencies of the single particle perturbations have been obtained for the high symmetry directions of the Brillouin zone. The dynamic matrices $D_{a\beta}(k+q_{i})$ of the protocrystals were calculated taking into account a certain number of the force constant of the influential coordination groups.

A new method for the determination of palladium has been developed based on the dispersive liquid–liquid microextraction preconcentration with UV-VIS spectrometry detection. In the proposed approach, 1-[(5-(3-nitrobenzyl)-1,3-thiazol-2-yl)diazenyl]naphthalen-2-ol (PNBTAN) was used as a new chelating agent, and methyl isobutyl ketone and ethanol were selected as extraction and dispersive solvents. The limit of detection (LOD), based on the signal-to-noise (S/N) ratio of 3, was 0.093 µg mL–1. Linearity was observed over the range of 0.24-1.437 µg mL–1 with the correlation coefficient (R) of 0.9993. The developed method has been successfully tested and applied to the determination of trace amounts of palladium in real objects. Analytical properties of PNBTAN and its complexes with palladium were investigated by theoretical calculations and experimental spectrophotometric method. Electron localization function, Fukui function, and molecular electrostatic potential isosurfaces were analyzed as reactivity descriptors for the explanation of the PNBTAN chelation ability. DFT analysis of eleven possible structures of the Pd:PNBTAN (1:2) complex has established the preferred formation of six-membered -O-Pd-N = N- containing cycles. According to the TD-DFT calculations, the experimentally observed bands at 747 and 680 nm in the UV-VIS spectrum of the Pd:PNBTAN (1:2) complex were assigned to the HOMO→LUMO and HOMO→LUMO+1 electron transitions, respectively.

Previous findings in the chemistry of 5-amino-1,2,4-triazol-3-thioles show the possibility of protonation of such systems on the nitrogen atom in position 1 of the triazole ring. To expand the molecular design synthetic strategies for triazole systems, it was suggested that the weakening of the basicity of the guanidine fragment via the introduction of a phenyl ring from one side and addition of a flexible 3-(carboxymethyl)sulfanyl moiety in position 3 of the cycle can lead to the formation of a triazole compound that would attach a proton on the nitrogen atom in the second position of the ring. Synthesis of the model 3-[(carboxymethyl)sulfanyl]-4-phenyl-5-phenylamino-4H-1,2,4-triazole via the selective S-alkylation of known 4-phenyl-5-phenylamino-1,2,4-triazole-3-thione has been performed. The synthesized triazole amino acid was converted into a corresponding hexabromotellurate salt which has been further explored and characterized via DFT, NMR and XRD methods.

The solvatochromic effect of solvents on the absorption and fluorescence spectra of three carbocyanine dyes, namely 1,1′,3,3,3′,3′-hexamethylindocarbocyanine chloride (HIC); 1,1′,3,3,3′,3′-hexamethylindodicarbocyanine iodide (HIDC); and 3,3′-diethyloxadicarbocyanine iodide (DODC), have been investigated. The experimental ground and excited-state dipole moments of the dyes have been estimated via the well-known models by Lippert-Mataga, Bakhshiev, Kawski-Chamma-Viallet, and the Dimroth-Reichardt’s empirical model. The influence of the solvation effect on the luminescence quantum yields was also examined and a strong correlation between the luminescence quantum yield values and the solvent viscosity was established. The fluorescence signal enhancement sensitivities between dyes were compared based on the Forster-Hoffmann equation. DFT and TDDFT calculations at the CAM-B3LYP/6-31G(d,p) level of theory were performed for the analysis of the nature of the electron transitions in absorption and excitation processes. Six phases different in polarity were considered during these computations, namely the gas, toluene, chloroform, acetone, methanol, and water. Transition electron density plots, Mulliken atomic partial charges, and Mayer bond orders were used for the analysis of the redistribution of electron density upon excitation. The specific behavior of the dyes in the glycerol medium was interpreted via the analysis of non-covalent interactions between the dye and glycerol molecules in terms of the reduced density gradient method.

The 1-[(5-Benzyl-1,3-thiazol-2-yl)diazenyl]naphthalene-2-ol (BnTAN) is a recently synthesized azo dye that can act as a tridentate ligand in complexes with transition metals. In a series of previous works, this analytical reagent was shown to be applicable for selective, reliable, express and relatively inexpensive determination of heavy metals in different objects through the spectrophotometric technique. Although the action of 1-(2-thiazolylazo)-2-naphthol (TAN) dyes as tridentate ligands has been suggested in the literature long time ago, due to the lack of experimental data, it was necessary to investigate the mechanism of formation and the structure of BnTAN complexes with the such transition metals as Cu(II), Zn(II) and Cd(II). Furthermore, the reactivity and properties of different acidity forms and conformers of BnTAN and related TAN dyes were not fully defined, so the determination of these properties by analysis of wavefunction was also necessary. Two standard spectrophotometric methods and voltammetric technique were used to determine the composition of complex of BnTAN with metals ions. All three experimental methods indicate that coordination ratio of metal:dye is equal to 1:2. Moreover, this study reports the stability and geometry of conformers of different forms (anionic/neutral/cationic) of BnTAN, along with a detailed analysis of electronic properties, reactivity and aromaticity of the most stable conformers of BnTAN forms. Each of the above forms has some difference in position of benzyl ring against the thiazole moiety, which is explained in terms of attraction and repulsion of these two fragments induced by partial atomic charges. The crucial influence of hydrogen bond and weak non-covalent interactions between naphthyl, aza- and thiazolyl fragments has been established. The quantum chemical calculations have shown that partial atomic charges of anionic, neutral and cationic forms can explain the reactivity of each BnTAN form, and have also clarified the mechanism of formation of metal complex through the connection of metal with phenol oxygen, thiazolyl nitrogen and one nitrogen of aza group – thus giving two five-membered metal-containing cycles and confirming that BnTAN acts as a tridentate ligand. The obtained results introduce novel and crucial information which can assist in understanding the mechanism of complex formation of BnTAN and display the strength and level of detail of applying quantum chemical methods to reveal the reactivity, energy properties, and electronic properties of this new dye.

The acid-base properties of Allura Red AC and Ponceau 4R azo dyes were investigated by spectrophotometric, potentiometric and tristimulus colourimetry methods. Ionization constants of the functional groups were also found in aqueous solutions of the dyes. It was discovered that the wavelength of the maximum light absorption of Allura Red AC and Ponceau 4R solutions does not change significantly over a wide pH range. As a result, spectrophotometric methods yield little information for assessing the acid-base properties of the dyes. It was shown with a help of the tristimulus colourimetry method that it is possible to determine the ionization constants of the functional groups of the dyes even when there is significant overlap of the absorption bands of the acid-base forms. The basic spectrophotometric characteristics of the main forms of Allura Red AC and Ponceau 4R in water and organic solvents were calculated. The molar absorbance coefficients of azo forms were shown to increase as the dielectric permittivity of the solvent increases. It was determined that in aqueous solution the dyes exist in the azo form over a wide range of acidity – pH 2–12 for Allura Red AC ( λ max = 505 nm; e λ = 3.1·10 4 dm 3 mol −1 cm −1 ) and 1–13 for Ponceau 4R ( λ max = 510 nm; e λ = 1.7·10 −4 dm 3 mol −1 cm −1 ). The most probable protonation/deprotonation schemes were theoretically determined for Allura Red AC and Ponceau 4R using DFT calculations.

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 set of effective ionic radii corresponding to different coordination numbers (CNs) and compatible with the radii system by Shannon [Acta Cryst.(1976), A32, 751–767] has been derived for ammonium: 1.40 Å (CN = IV), 1.48 Å (CN = VI), 1.54 Å (CN = VIII) and 1.67 Å (CN = XII). The bond-valence parametersr0= 2.3433 Å andB= 0.262 Å have been determined for ammonium–fluorine bonds.

A calculation scheme based on the bond valence model and involving the distance least squares refinement procedure has been developed for predicting the crystal structures of the ideal ternary oxide pyrochlores.

3,7,8-Trihydroxy-3-methyl-10-oxo-4,10-dihydro-1H,3H-pyrano [4,3-b]chromene-9-carboxylic acid is a structurally well-characterized fulvic acid (FA) capable to act as a polyfunctional bidentate ligand in the complexes with metal ions. Investigations of the formation mechanisms and structure of the above-mentioned FA complexes with bivalent metals [Cd(II), Cu(II), Mg(II), Ni(II), Pb(II) and Zn(II)] are presently an actual and trending topic in the modern chemistry of humic and fulvic acids. Furthermore, the importance of the theoretical DFT investigations of binding of metals with fulvic acids is stipulated by the lack of the relevant experimental structural data for such complexes. The quantum chemical calculations have shown that, of the four possible FA tautomers, the two FA forms are more stable. The wavefunction analysis and computed reactivity descriptors (electrostatic potential, Hirshfeld surface analysis, natural population analysis charges, and condensed Fukui indexes) give the insight on the properties and reactive ability of these two different forms of the FA. The computed thermochemical parameters of the ion-exchange reaction explain the metal binding affinity and selectivity of the FA forms.

The applicability of cetylpyridinium chloride for potentiometric titration of lipophilic anions has been studied. The specially developed cetylpyridinium-selective plasticized electrode has been used for the investigation of the mechanism of interaction between the cetylpyridinium cation and lipophilic anions, which obviously goes through the association reaction resulting in the formation of water-insoluble precipitates. The investigated 54 anions were placed in the selectivity row that strongly correlates with lipophilicity. Additionally, an attempt has been made to find a simple and reliable descriptor suitable for prediction of the value of the end point potential break and thus indicating the applicability of the described potentiometric method for determination of untested lipophilic anions of interest. It has been established that despite being well known lipophilicity estimators, molar weight, octanol–water distribution coefficient logP, logarithm of solubility logS, and hydrophilicity-lipophilicity index can not be separately used for directly predicting the end point potential break values. However, simultaneous analysis of the above descriptors by using the multiple linear regression technique has resulted in the development of a reasonable QSPR model for the estimation of the potential break values near the end point.

A simple calculation scheme based on the Ahrens ionic radii system is proposed for predicting the lattice parameters of the A I A II B II 2F7 disordered cubic fluoride pyrochlores.

Using the multiple linear regression technique, an efficient empirical model based on the weighted ionic radii has been developed for predicting the cell parameters of the high symmetry argyrodite structures crystallizing in the cubic space group F-43 ​m (No. 216) and having no strictly stoichiometric chemical compositions.

A new thiazolylazo structure, 1-[(5-(3-nitrobenzyl)-1,3-thiazol-2-yl)diazenyl]naphthalen-2-ol (NBnTAN), has been synthesized for the first time. The geometric parameters and properties of the new dye were studied using spectroscopic, DFT and semiempirical methods through the computation of different electronic descriptors (aromaticity, frontier molecular orbitals, dipole moments, partial atomic charges). The solvation effect of different organic liquids on the absorption spectra of the reagent has been studied. 1H, 13C, COSY, HSQC and HMBC NMR, UV–Vis and IR spectra were used to confirm the reagent structure. It has been shown that NBnTAN forms complex compounds with a number of transition metals, allowing the development of selective methods for the determination of these metals.

A few different theoretical methods for assigning the partial atomic charges were benchmarked for calculation of the hydrophilic/lipophilic index (HLI). The coefficients were selected to produce the best correlation of the HLI values with the experimental octanol-water partition. Different parameters were checked in calculations of partial charges to get the best performance of the HLI values obtained. Thus, four partitioning schemes (Coulson, Mulliken, Merz-Kollman, Ford-Wang) were benchmarked for calculations of atomic charges with six semiempirical methods (AM1, PM3, RM1, PM6, PM6-D3H4, PM7). Moreover, five distinct types of partial atomic charges (Mulliken, Hirshfeld, Löwdin, CHELPG, NPA), obtained at the Hartree-Fock and DFT levels of theory with three basis sets, were tested for their ability to produce the HLI values with the best correlation to experimental logP coefficients of 50 mono-charged organic anions. In the case of the semiempirical methods, the best correlation between the HLI and logP values (the correlation coefficient r = 0.9216) was obtained with the AM1 Ford-Wang parametric electrostatic potential charges. The Mulliken and Coulson charges calculated with the PM7 method can be used as an alternative to AM1, with the r values of 0.9107 and 0.8984, respectively. In the case of the DFT, the PBE/def2-TZVP natural population analysis charges produce the best correlation (r = 0.9220). Nevertheless, in spite of a marginally lower performance (r = 0.9159), the NPA charges computed at the PBE/def2-SVP level are more robust and can be regarded as the optimum choice for calculating the HLI values. Graphical abstract The hydrophilic/lipophilic index (HLI).

The extended variant of the bond valence (s)–bond length (r) correlation curve for boron(III)–oxygen bonds has been closely approximated using the three-parameter function s = [k/(r – l)] – m, where s is measured in valence units (vu), r is measured in Å, k = 0.53 Å·vu, l = 0.975(1) Å and m = 0.32 vu. The function s = exp[(r 0 – r)/b] traditionally used in the modern bond valence model requires the separate set of the bond valence parameters (r 0 = 1.362 Å; b = 0.23 Å) in order to approximate the above s–r curve for the bonds shorter than ∼1.3 Å.

Cu7PS6 crystals were grown using direct crystallisation from the melt (Bridgman–Stockbarger technique). The crystal structure of Cu7PS6 was determined by X-ray powder diffraction. Cu7PS6 crystallise in the cubic structure, space group P213 (No. 198), the lattice parameter a = 9.6706(1) Å, formula units per cell Z = 4. Electrical properties of Cu7PS6 crystals were studied in the frequency range 10–1010 Hz and in the temperature interval 296–351 K. The performed analysis shows that the Cu7PS6 crystals are mixed electron-ionic conductors with some growth defects.

The oxidation-state independent `bond valence (s)versusbond length (r)' correlation curve for manganese–oxygen bonds has been closely approximated using the modified two-parameter Trömels=f(r) function [Trömel (1983).Acta Cryst.B39, 664–669],s= [(r0−l)/(r−l)]2, wherer0= 1.763 (2) Å andl= 1.148 (9) Å. Ther0andlrefinable parameters of the above function can be regarded as the alternative bond-valence parameters intended for use in the modern bond-valence model [Brown (2009).Chem. Rev.109, 6858–6919] in cases where the traditional bond-valence parameters (r0;n) and (r0;b) fail.

Single crystals of the copper-containing Cu7-nPS6-nBrn (0 ≤ n ≤ 1) argyrodites have been grown by direct solidification using the Bridgman–Stockbarger technique. All compounds have been structurally characterized using the X-ray powder diffraction technique. Compositional dependencies of electrical conductivity and activation energy were studied. Two simple structural indicators have been proposed in order to predict the ionic conductivity in argyrodites under investigations. Interrelation between structure and mechanism of ionic conductivity was discussed.

For the crystal structures of oxoborates, the value of ∼ 1.2 A can be regarded as the lower physical limit for BIII—O bond lengths. The oxoborate crystal structures with BIII—O bond lengths shorter than ∼ 1.2 A have been found to be either doubtful or clearly erroneous.

The improved values of the bond-valence parameters for the Sb3+/O2–ion pair,r0= 1.927 Å andb= 0.446 Å, have been deduced from the crystal structures of the α and β polymorphs of Sb2O3and from the set of precisely determined complex structures containing [Sb3+On] coordination shells.

The crystal structure of Sb 3 O 6.5 has been refined using the Rietveld analysis of X-ray powder diffraction data. The refinement procedure was stopped when the intensity residual R B = 6.1% had been reached. Sb 3 O 6.5 crystallizes in a cubic structure of the defect pyrochlore type, space group Fd -3 m (No. 227), with the lattice parameter a = 10.3024(5) A, Z = 8, D c = 5.701(1) g/cm 3 .

The crystal structure of the ternary iodide Cs2TeI6 has been refined by Rietveld analysis of X-ray powder diffraction data. The refinement procedure was stopped when the intensity residual RB = 3.7 % had been reached. Cs2TeI6 crystallizes in the cubic K2PtCl6 structure type, space group Fm-3m (No. 225), with the lattice parameter a = 11.6939(8) A, Z = 4, Dc = 4.797(1) g/cm . The reliability of the structural model obtained for Cs2TeI6 in the Rietveld refinement was confirmed by a bond-valence analysis of the structure. For the first time, the bond-valence parameters (r0 = 2.782 A and b = 0.37 A) have been determined for the Te /I ion pair, from a set of 14 well-determined coordination shells [TeIn]. These parameters show a reasonably high performance and can be recommended for routine bond-valence analyses of structures containing Te–I chemical bonds.

The crystal structure of Hg2Sb2O7 has been refined using X-ray powder diffraction technique. Hg2Sb2O7 crystallizes in the cubic pyrochlore structure type, space group F d 3 ¯ m , with the lattice parameter a = 10.3525(5) A, Z = 8, Dc = 9.060(1) g/cm3. The Rietveld refinement procedure was stopped when the intensity residual RB = 3.25% had been reached. In the bond-valence analysis of the crystal structure of Hg2Sb2O7, the values of the bond-valence parameters reported for the Sb5+/O2− ion pair have been found to be doubtful. Using the new calculation scheme, the improved bond-valence parameters for the Sb5+/O2− ion pair (r0 = 1.908 A and b = 0.409 A) have been derived from the crystal structure of Sb2O5.

Li2B4O7:Cu single-crystal annealing in the reducing environment results in a sharp drop of intensity of thermoluminescence (TSL) and X-ray luminescence (XL) peaks. It was suggested that during annealing in the reducing environment, an oxygen vacancy is produced in the LTB structure at the bridging oxygen atom site. Oxygen vacancy charge compensation takes place at the expense of reduction of the doping Cu+ ion to the Cu0 state. In this case the A0-type thermoluminescence center formation mechanism due to irradiation becomes impossible.

The influence of reducing annealing and repeated oxidizing annealing of the Li2B4O7:Mn single crystals on their thermostimulated luminescence (TSL) and X-ray luminescence (XL) has been studied. Because of the oxygen vacancies formation and the dopant ions reduction, the reducing annealing results in a drastic decrease of the luminescence intensity along with the simultaneous shift of a part of the maxima and redistribution of the peak intensities. The repeated annealing in the oxidizing environment leads only to the partial reduction of the luminescent properties of the Li2B4O7:Mn crystals.

The relationship between the bond valencesand the thermal expansion rate of chemical bonds (dr/dT) has been closely approximated by using the alternative three-parameter empirical model (dr/dT) = (u+vs)–1/w, whereu,vandware the refinable parameters. Unlike thes–(dr/dT) model developed by Brownet al.[(1997),Acta Cryst.B53, 750–761], this alternative model can be optimized for particulars–(dr/dT) datasets in the least-squares refinement procedure. For routine calculations of the thermal expansion rates of chemical bonds, the alternative model with the parametersu= −63.9,v= 2581.0 andw= 0.647 can be recommended.

The crystal structures of Tl 2 TeBr 6 and Tl 2 Tel 6 have been determined using X-ray powder diffraction techniques. Tl 2 TeBr 6 crystallizes in the tetragonal space group P4/mnc, with the lattice parameters: a = 7.468(1) A, c = 10.682(2) A, Z = 2. Tl 2 TeI 6 crystallizes in the monoclinic space group P2 1 /c, with the lattice parameters: a = 7.765(2) A, b = 8.174(2) A, c = 13.756(5) A, β = 124.2(1)°, Z = 2. The Rietveld refinement procedures were stopped when the intensity residuals R B = 0.038 for Tl 2 TeBr 6 and R B = 0.049 for Tl 2 TeI 6 had been reached. The crystal structures of both investigated ternary halides belong to the large family of K 2 PtC 6 -related structures.

The `bond valence (s)–bond length (r)' correlation reported earlier for H—O bonds [Brown (2009). Chem. Rev. 109, 6858–6919] has been closely approximated using the function s = (α − βr)1/γ, where α = 1.185 (10), β = 0.321 (8) and γ = 0.36.

The compound Rb3Bi2I9 was synthesized by melting a stoichiometric mixture of RbI and BiI3 and annealing for 1 month some degrees below the melting temperature of 785±5K; a large single crystal of the title compound has been grown from the melt by directional solidification using the vertical Bridgman-Stockbarger technique. X-ray structure determination of the compound involved single-crystal diffractometry, direct and Patterson methods and least-squares refinement. Rb3Bi2I9 exhibits a new type of crystal structure, crystallizing in the monoclinic space group Pc with unit-cell parameters a=14.690(4), b=8.195(2), c=25.645(6) A, β=125.39(2)°, V=2517(2) A3, Z=4. The unit-cell of Rb3Bi2I9 has six pseudohexagonal RbI3 layers which are stacked along the direction near to the normal of the XY plane. Each BiI6 octahedron shares three corners with three other octahedra to form parallel Bi2I9 corrugated layers intersecting Z axis of the structure at an angle near 120°.

The calculation scheme for determining the bond-valence parameters (r 0 and b) resulting in the exact solution of the bond-valence sum rule for a given set of coordination shells is presented.

The compound Rb3Bi2I9 was synthesized by melting a stoichiometric mixture of RbI and BiI3 and annealing for 1 month some degrees below the melting temperature of 785±5K; a large single crystal of the title compound has been grown from the melt by directional solidification using the vertical Bridgman-Stockbarger technique. X-ray structure determination of the compound involved single-crystal diffractometry, direct and Patterson methods and least-squares refinement. Rb3Bi2I9 exhibits a new type of crystal structure, crystallizing in the monoclinic space group Pc with unit-cell parameters a=14.690(4), b=8.195(2), c=25.645(6) A, β=125.39(2)°, V=2517(2) A3, Z=4. The unit-cell of Rb3Bi2I9 has six pseudohexagonal RbI3 layers which are stacked along the direction near to the normal of the XY plane. Each BiI6 octahedron shares three corners with three other octahedra to form parallel Bi2I9 corrugated layers intersecting Z axis of the structure at an angle near 120°.

Using the least-squares refinement procedure, high-performance Brown–Wu bond-valence parameters, r 0 and n, reported for the Sn2+/O2−, Sb3+/O2−, Te4+/O2− and I5+/O2− ion pairs have been converted into the commonly used bond-valence parameters, r 0 and b. The r 0 and b values obtained can be recommended as a replacement for the conventional bond-valence parameters based on the `universal constant' b = 0.37 Å.

The crystal structure of Hg2Sb2O7 has been refined using X-ray powder diffraction technique. Hg2Sb2O7 crystallizes in the cubic pyrochlore structure type, space group F d 3 ¯ m , with the lattice parameter a = 10.3525(5) A, Z = 8, Dc = 9.060(1) g/cm3. The Rietveld refinement procedure was stopped when the intensity residual RB = 3.25% had been reached. In the bond-valence analysis of the crystal structure of Hg2Sb2O7, the values of the bond-valence parameters reported for the Sb5+/O2− ion pair have been found to be doubtful. Using the new calculation scheme, the improved bond-valence parameters for the Sb5+/O2− ion pair (r0 = 1.908 A and b = 0.409 A) have been derived from the crystal structure of Sb2O5.

Systematic variations of the bond-valence sums calculated from the poorly determined bond-valence parameters [Sidey (2008), Acta Cryst. B64, 515–518] have been illustrated using a simple graphical scheme.