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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.

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.

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.

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.

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 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 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.

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 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°.