Benzoyl transfer reactivities of racemic 2,4-di-O-acyl-myo-inosityl 1,3,5-orthoesters in the solid state: molecular packing and intermolecular interactions correlate with the ease of the reaction

Racemic 2,4-di-O-acyl-myo-inosityl 1,3,5-orthoesters undergo transesterification catalyzed by sodium carbonate with varying ease of reaction in the solid state; reactions in solution and melt do not show such varied differences. An interesting crystal of a 1:1 molecular complex of highly reactive racemic 2,4-di-O-benzoyl-myo-inosityl 1,3,5-orthoformate and its orthoacetate analogue exhibited better reactivity than the latter component alone. Single-crystal X-ray structures of the reactants have been correlated with the observed differences in the acyl-transfer efficiencies in the solid state. Although each of the derivatives helically self-assembles around the crystallographic 2(1) axis linked through O-H...O hydrogen bonding, the pre-organization of the reactive groups (C=O [El] and OH [Nu]), C-H...O and the C-H...pi interactions are significantly more favourable for the reactive derivatives than the less reactive ones. Bond-length distributions also showed differences; the O-C bond of the axial benzoyl group, which gets cleaved during the reaction, is longer (1.345-1.361 A) relative to the chemically equivalent O-C bond of the equatorial benzoyl group (1.316-1.344 A) in the reactive derivatives. These bond-length differences are not significant in the less reactive derivatives. The overall molecular organization is different too; the strikingly discrete helices, which may be viewed as "reaction tunnels" and are held by interhelical interactions, are clearly evident in the reactive derivatives in comparison with the less reactive ones.     

Hydrogen‐bonding patterns in bis[2,4,6‐triazaniumylcyclohexane‐1,3,5‐tris(olate)‐κ3O,O′,O′′]germanium(IV) tetrachloride hexahydrate

A first preliminary report on the crystal structure of a hydrated salt formulated as [Ge(taci)₂]Cl₄·13H₂O (taci is 1,3,5‐triamino‐1,3,5‐trideoxy‐cis‐inositol) appeared more than 20 years ago [Ghisletta (1994). PhD thesis, ETH Zürich. Switzerland]. At that time it was not possible to discriminate unambiguously between the positions of some of the chloride ions and water O atoms, and disorder was thus postulated. In a new determination, a conclusive scheme of hydrogen bonding proves to be a particularly appealing aspect of the structure. Single crystals of the title compound, C₁₂H₃₀GeN₆O₆⁴⁺·4Cl⁻·6H₂O or [Ge(taci)₂]₂Cl₈·12H₂O, were grown from an aqueous solution by slow evaporation of the solvent. The two [Ge(taci)₂]⁴⁺ cations exhibit a double‐adamantane‐type structure with exclusive O‐atom coordination and approximate D_3d symmetry. The taci ligands adopt a zwitterionic form with deprotonated hydroxy groups and protonated amino groups. Both cations are hydrogen bonded to six water molecules. The structure of the hydration shell of the two cations is, however, slightly different. The {[Ge(taci)₂]·6H₂O}⁴⁺ aggregates are interlinked in all three dimensions by further hydrogen bonds of the types N—H...Cl...H—N, N—H...O(H)₂...H—N, (Ge)O...H—O(H)...H—N, N—H...O(H)—H...Cl...H—N, (Ge)O...H—O—H...Cl...H—N, N—H...O(H)—H...Cl...H—(H)O...H—N, (Ge)O...H—O—H...Cl...H—(H)O...H—N and Ge(O)...H—O—H...Cl...H—O—H...O(Ge).     

Hydrogen bonding in polyamino‐polyalcohols: a monohydrated cocrystal of 1,3‐diamino‐5‐azaniumyl‐1,3,5‐trideoxy‐cis‐inositol iodide and 1,3,5‐triamino‐1,3,5‐trideoxy‐cis‐inositol

In the title monohydrated cocrystal, namely 1,3‐diamino‐5‐azaniumyl‐1,3,5‐trideoxy‐cis‐inositol iodide–1,3,5‐triamino‐1,3,5‐trideoxy‐cis‐inositol–water (1/1/1), C₆H₁₆N₃O₃⁺·I⁻·C₆H₁₅N₃O₃·H₂O, the neutral 1,3,5‐triamino‐1,3,5‐trideoxy‐cis‐inositol (taci) molecule and the monoprotonated 1,3‐diamino‐5‐azaniumyl‐1,3,5‐trideoxy‐cis‐inositol cation (Htaci⁺) both adopt a chair conformation, with the three O atoms in axial and the three N atoms in equatorial positions. The cation, but not the neutral taci unit, exhibits intramolecular O—H...O hydrogen bonding. The entire structure is stabilized by a complex three‐dimensional network of intermolecular hydrogen bonds. The neutral taci entities and the Htaci⁺ cations are each aligned into chains along [001]. In these chains, two O—H...N interactions generate a ten‐membered ring as the predominant structural motif. The rings consist of vicinal 2‐amino‐1‐hydroxyethylene units of neighbouring molecules, which are paired via centres of inversion. The chains are interconnected into undulating layers parallel to the ac plane, and the layers are further held together by O—H...N hydrogen bonds and additional interactions with the iodide counter‐anions and solvent water molecules.     

Crystal structures of the pyrazinamide–p‐aminobenzoic acid (1/1) cocrystal and the transamidation reaction product 4‐(pyrazine‐2‐carboxamido)benzoic acid in the molten state

The synthesis of pharmaceutical cocrystals is a strategy to enhance the performance of active pharmaceutical ingredients (APIs) without affecting their therapeutic efficiency. The 1:1 pharmaceutical cocrystal of the antituberculosis drug pyrazinamide (PZA) and the cocrystal former p‐aminobenzoic acid (p‐ABA), C₇H₇NO₂·C₅H₅N₃O, (1), was synthesized successfully and characterized by relevant solid‐state characterization methods. The cocrystal crystallizes in the monoclinic space group P2₁/n containing one molecule of each component. Both molecules associate via intermolecular O—H...O and N—H...O hydrogen bonds [O...O = 2.6102 (15) Å and O—H...O = 168.3 (19)°; N...O = 2.9259 (18) Å and N—H...O = 167.7 (16)°] to generate a dimeric acid–amide synthon. Neighbouring dimers are linked centrosymmetrically through N—H...O interactions [N...O = 3.1201 (18) Å and N—H...O = 136.9 (14)°] to form a tetrameric assembly supplemented by C—H...N interactions [C...N = 3.5277 (19) Å and C—H...N = 147°]. Linking of these tetrameric assemblies through N—H...O [N...O = 3.3026 (19) Å and N—H...O = 143.1 (17)°], N—H...N [N...N = 3.221 (2) Å and N—H...N = 177.9 (17)°] and C—H...O [C...O = 3.5354 (18) Å and C—H...O = 152°] interactions creates the two‐dimensional packing. Recrystallization of the cocrystals from the molten state revealed the formation of 4‐(pyrazine‐2‐carboxamido)benzoic acid, C₁₂H₉N₃O₃, (2), through a transamidation reaction between PZA and p‐ABA. Carboxamide (2) crystallizes in the triclinic space group P with one molecule in the asymmetric unit. Molecules of (2) form a centrosymmetric dimeric homosynthon through an acid–acid O—H...O hydrogen bond [O...O = 2.666 (3) Å and O—H...O = 178 (4)°]. Neighbouring assemblies are connected centrosymmetrically via a C—H...N interaction [C...N = 3.365 (3) Å and C—H...N = 142°] engaging the pyrazine groups to generate a linear chain. Adjacent chains are connected loosely via C—H...O interactions [C...O = 3.212 (3) Å and C—H...O = 149°] to generate a two‐dimensional sheet structure. Closely associated two‐dimensional sheets in both compounds are stacked via aromatic π‐stacking interactions engaging the pyrazine and benzene rings to create a three‐dimensional multi‐stack structure.     

Tuning the energy level of TAPC: crystal structure and photophysical and electrochemical properties of 4,4′‐(cyclohexane‐1,1‐diyl)bis[N,N‐bis(4‐methoxyphenyl)aniline]

The energy level of a hole‐transporting material (HTM) in organic electronics, such as organic light‐emitting diodes (OLEDs) and perovskite solar cells (PSCs), is important for device efficiency. In this regard, we prepared 4,4′‐(cyclohexane‐1,1‐diyl)bis[N,N‐bis(4‐methoxyphenyl)aniline] ( TAPC‐OMe ), C₄₆H₄₆N₂O₄, to tune the energy level of 4,4′‐(cyclohexane‐1,1‐diyl)bis[N,N‐bis(4‐methylphenyl)aniline] ( TAPC ), which is a well‐known HTM commonly used in OLED applications. A systematic characterization of TAPC‐OMe , including ¹H and ¹³C NMR, elemental analysis, UV–Vis absorption, fluorescence emission, density functional theory (DFT) calculations and single‐crystal X‐ray diffraction, was performed. TAPC‐OMe crystallized in the triclinic space group P, with two molecules in the asymmetric unit. The dihedral angles between the central amine triangular planes and those of the phenyl groups varied from 26.56 (9) to 60.34 (8)° due to the steric hindrance of the central cyclohexyl ring. This arrangement might be induced by weak hydrogen bonds and C—H…π(Ph) interactions in the extended structure. The emission maxima of TAPC‐OMe showed a significant bathochomic shift compared to that of TAPC . A strong dependency of the oxidation potentials on the nature of the electron‐donating ability of substituents was confirmed by comparing oxidation potentials with known Hammett parameters (σ).     

Masking of Lewis acidity trends in the solid‐state structures of trichlorido‐ and tribromido(2,2′:6′,2′′‐terpyridine‐κ3N,N′,N′′)gallium(III)

The molecular structures of trichlorido(2,2′:6′,2′′‐terpyridine‐κ³N,N′,N′′)gallium(III), [GaCl₃(C₁₅H₁₁N₃)], and tribromido(2,2′:6′,2′′‐terpyridine‐κ³N,N′,N′′)gallium(III), [GaBr₃(C₁₅H₁₁N₃)], are isostructural, with the Ga^III atom displaying an octahedral geometry. It is shown that the Ga—N distances in the two complexes are the same within experimental error, in contrast to expected bond lengthening in the bromide complex due to the lower Lewis acidity of GaBr₃. Thus, masking of the Lewis acidity trends in the solid state is observed not only for complexes of group 13 metal halides with monodentate ligands but for complexes with the polydentate 2,2′:6′,2′′‐terpyridine donor as well.     

Synthesis and crystal structures of a 3‐acetylated (20S,24S)‐ocotillol‐type saponin and its C‐24 epimer

In order to study the in vivo protective effect on myocardial ischemia, (20S ,24R )‐epoxydammarane‐12β,25‐diol, (V), and (20S ,24S )‐epoxydammarane‐12β,25‐diol, (VI), were synthesized through a novel synthetic route. Two key intermediates, namely (20S ,24R )‐3‐acetyl‐20,24‐epoxydammarane‐3β,12β,25‐triol, (III) [obtained as the hemihydrate, C₃₂H₅₄O₅·0.5H₂O, (IIIa ), and the ethanol hemisolvate, C₃₂H₅₄O₅·0.5C₂H₅OH, (IIIb ), with identical conformations but different crystal packings], and (20S ,24S )‐3‐acetyl‐20,24‐epoxydammarane‐3β,12β,25‐triol, C₃₂H₅₄O₅, (IV), were obtained during the synthesis. The structures were confirmed by ¹H NMR, ¹³C NMR and HRMS analyses, and single‐crystal X‐ray diffraction. Molecules of (IIIa ) are extended into a two‐dimensional network constructed with water molecules linked alternately through intermolecular O—H…O hydrogen bonds, which are further stacked into a three‐dimensional network. Compound (IIIb ) contains two completely asymmetric molecules, which are linked in a disordered manner through intermolecular C—H…O hydrogen bonds. While the crystal stacks in compound (IV) are linked via weak C—H…O hydrogen bonds, the hydrogen‐bonded chains extend helically along the crystallographic b axis.