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Two crystal structures of 2-4-6 trinitrotoluene (TNT) are given, the monoclinic form (a 0 = 1.49113 (1) nm, b 0 = 0.60340 (1) nm, c 0 = 2.08815(3) nm, β = 110.365 (1)°, V = 1.76137 (4) nm3, space group = P21/a, T = 100 K) and the orthorhombic form (a 0 = 1.4910 (2) nm, b 0 = 0.6031 (2) nm, c 0 = 1.9680 (4) nm, V = 1.7706 (7) nm3, space group = Pca21, T = 123 K). Of these two forms, the most stable is the monoclinic and the less stable is the orthorhombic form. These two polymorphs are shown to be orientational, rather than configurational in character. Due to their restricted molecular motifs, no strong hydrogen bonding exists and the crystalline form is dominated by van der Waals type forces. The two structures are shown to be closely related and an analysis of the two structures shows that they are effectively large scale polytypes. Calorimetric studies show that the two polymorphs are monotropic and that the enthalpy of transformation is very low, concurring with the similarity shown by the diffraction data and calculated lattice energies. The thermal expansion coefficients are defined, and it is shown that both polymorphs have similar thermal expansions.

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One hundred 4,4'-disubstituted benzenesulfonamidobenzenes, X-C(6)H(5)-SO(2)-NH-C(6)H(5)-Y, where X, Y = NO(2), CN, CF(3), I, Br, Cl, F, H, Me, OMe, have been synthesized and their crystal structures determined. The resulting set of 133 structures, which includes polymorphic forms, is used to make a comparative study of the molecular packing and the nature of the intermolecular interactions, including the formation of hydrogen-bonding motifs and the influence of the two substituents X and Y on these features. Nine distinct supramolecular connectivity motifs of hydrogen bonding are encountered. There are 74% of all the structures investigated which exhibit one of two motifs based on N-H...O=S interactions, a dimer or a chain. There are three other, infrequent motifs, also employing N-H...O=S links, which exhibit more complexity. Four different chain motifs result from either N-H...O=N, N-H...C[triple-bond]N or N-H...OMe interactions, arising from the presence of a nitro (position Y), nitrile (X or Y) or methoxy (Y) substituent. The program XPac [Gelbrich & Hursthouse (2005). CrystEngComm, 7, 324-336] was used to systematically analyse the packing relationships between crystal structures. Similar discrete (zero-dimensional) and extended (one-dimensional and two-dimensional) structure components, as well as cases of isostructurality were identified. A hierarchy for the classification of the 56 distinct structure types of this set is presented. The most common type, a series of 22 isostructures containing the simple centrosymmetric N-H...O=S-bonded dimer, is discussed in detail.

or I are reported. Comparisons carried out with the program XPac show that all investigated structures display a common 3D arrangement of N-H … N bonded centrosymmetric dimers. This isostructural series is exceptional in its completeness and in the diversity of the substituents involved. Accordingly, the XPac dissimilarity index x, a measure of how far two structures deviate from perfect geometrical similarity, varies from 0.9 for the interchange R 1 = Br A Cl to 9.5 for the simultaneous interchange of R 1 = I A H and R 2 = CF 3 A I. XPac plots of individual dissimilarity parameters have been used to elucidate details of geometrical similarities and differences between structures. This indicated that the geometry is preserved most closely within bc-layers that are composed of 1D slipped stacks of N-H … N bonded dimers, with interlayer van der Waals interactions being dominated by R 1 … R 2 contacts. The main mode of geometrical adjustment for the size of R 1 is a parallel shift of neighbouring layers against one another in the direction perpendicular to the layer plane, whilst the relative orientations of molecules within each layer are altered to a much smaller extent, even for those structure pairs representing R 1 substituents that are very different in size. This study shows that the ability of two compounds to crystallise in fundamentally the same crystal structure depends not only on how much their molecules differ in shape but also, critically, on the specific tolerance characteristics of the crystal packing arrangement concerned. As a comparison with the present study, dissimilarity indices are reported for a set of 24 isostructural 4,49-substituted benzenesulfonamidobenzenes previously subjected to XPac analysis.

A comprehensive characterization (thermal, spectroscopic, crystallographic, temperature- and moisture-dependent stability, and transition characteristics) of solvates of aripiprazole (APZ) with methanol (1:1), ethanol (2:1), dichloroethane (2:1), and a monohydrate is presented. To gain insight into packing similarities and differences, the four hydrate/solvate crystal structures and five APZ modifications were compared using the program XPac. It was found that all forms apart from the hydrate are based on either a common dimeric or catemeric motif of H-bonded APZ molecules, and this analysis confirmed also the isostructurality of the three solvates and pointed to possible mechanisms for the desolvation of the solvates and the transformation between forms X° and I. The fact that the intermolecular interactions in the monohydrate are completely different from those found in the isostructural solvates was further confirmed by analyzing the Hirshfeld fingerprint plots. The desolvation of all solvated forms results in form III. The order of their measured stabilities correlates well with variations in the intermolecular APZ/solvent interactions. Additionally, solubility and solvent-mediated transition rates were determined in a 1-PrOH/water mixture (3:7) for transformations to the monohydrate from the metastable form III and from the thermodynamically stable form at room temperature (form X°).

Four series of dyes with dimethylamino electron donor groups and N‐R‐pyridinium (R = methyl Me, phenyl Ph, 2,4‐dinitrophenyl 2,4‐DNPh, or 2‐pyrimidyl 2‐Pym) electron acceptors are studied as their hexafluorophosphate salts. The intramolecular charge‐transfer (ICT) energies (Emax) of these compounds decrease within each of the series in the order R = Me > Ph > 2,4‐DNPh > 2‐Pym, as the electron‐accepting ability of the pyridinium ring increases. Hyper‐Rayleigh scattering with femtosecond 1300 or 800 nm lasers yields fluorescence‐free first hyperpolarizabilities β, and static first hyperpolarizabilities β0[H] are obtained via the two‐state model. Dipole moment changes Δμ12 for the ICT transitions obtained from Stark spectroscopy afford β0[S] values by using β0 = 3Δμ12(μ12)2/2(Emax)2 (μ12 = transition dipole moment). The β0[S] data show that the combination of pyridyl N‐arylation with conjugation extension affords large increases in β0. The β0[H] data generally agree with this conclusion, but resonance effects may explain some apparent anomalies. X‐ray structural studies on various salts reveal that the use of tosylate anions is not a generally applicable approach to engineering noncentrosymmetric structures of pyridinium salts. However, trans‐N‐phenyl‐4‐(4‐dimethylaminophenyl‐4‐buta‐1,3‐dienyl)pyridinium hexafluorophosphate adopts the polar space group Cc, and shows a very large powder second harmonic generation efficiency from a 1907 nm laser, which is similar to that of the well‐studied material trans‐4′‐(dimethylamino)‐N‐methyl‐4‐stilbazolium tosylate (DAST).