Two polymorphs of 5‐cyclohexyl‐5‐ethylbarbituric acid and their packing relationships with other barbiturates

Polymorph (Ia) (m.p. 474 K) of the title compound, C₁₂H₁₈N₂O₃, displays an N—H...O=C hydrogen‐bonded layer structure which contains R₆⁶(28) rings connecting six molecules, as well as R₂²(8) rings linking two molecules. The 3‐connected hydrogen‐bonded net resulting from these interactions has the hcb topology. Form (Ib) (m.p. 471 K) displays N—H...O=C hydrogen‐bonded looped chains in which neighbouring molecules are linked to one another by two different R₂²(8) rings. Polymorph (Ia) is isostructural with the previously reported form II of 5‐(2‐bromoallyl)‐5‐isopropylbarbituric acid (noctal) and polymorph (Ib) is isostructural with the known crystal structures of four other barbiturates.     

Silicon Analogues of Triarylmethanol Hosts. Inclusion Properties and Host–guest Structures: A Comparative Study

The simple triarylmethanol hosts, 2 and 4, and their silicon analogues, 1 and 3, have been studied for comparison of the formation of crystalline inclusion compounds. Clathrate formation experiments showed that replacement of the carbinol C atoms in 2 and 4 by Si atoms to give 1 and 3 resulted in a distinct increase of the capability to form inclusion compounds with organic guests, in particular with alcohols. Moreover, the naphthyl derivatives are much more efficient than the phenyl species, irrespective of the carbinol and silanol features. In order to investigate and compare the guest recognition modes and packing relations of hosts 1–4 in their crystalline inclusion compounds, 11 selected co-crystals, namely 1·DMSO (2:1), 3·EtOH (1:1), 3· i-PrOH (1:1), 3·acetone (1:1), 3·DMSO (1:1), 3·THF (1:1), 3·piperidine (1:1), 4·acetone (1:1), 4·DMSO (1:1), 4·1,4-dioxane (1:1) and 4·benzene (1:1), were studied by X-ray diffraction from single crystals. The survey contains additional 11 crystal structures from the literature and provides a detailed discussion of isostructurality relationships.Supplementary Data relevant to this publication have been deposited with the Cambridge Crystallographic Data Centre as supplementary publications nos. CCDC 274780–274790.     

Solvent‐mediated pseudo‐quadruple hydrogen‐bond motifs in three lamotrigine–carboxylic acid complexes

Lamotrigine, an antiepileptic drug, has been complexed with three aromatic carboxylic acids. All three compounds crystallize with the inclusion of N,N‐dimethylformamide (DMF) solvent, viz. lamotriginium [3,5‐diamino‐6‐(2,3‐dichlorophenyl)‐1,2,4‐triazin‐2‐ium] 4‐iodobenzoate N,N‐dimethylformamide monosolvate, C₉H₈Cl₂N₅⁺·C₇H₄IO₂⁻·C₃H₇NO, (I), lamotriginium 4‐methylbenzoate N,N‐dimethylformamide monosolvate, C₉H₇Cl₂N₅⁺·C₈H₈O₂⁻·C₃H₇NO, (II), and lamotriginium 3,5‐dinitro‐2‐hydroxybenzoate N,N‐dimethylformamide monosolvate, C₉H₈Cl₂N₅⁺·C₇H₃N₂O₇⁻·C₃H₇NO, (III). In all three structures, proton transfer takes place from the acid to the lamotrigine molecule. However, in (I) and (II), the acidic H atom is disordered over two sites and there is only partial transfer of the H atom from O to N. In (III), the corresponding H atom is ordered and complete proton transfer has occurred. Lamotrigine–lamotrigine, lamotrigine–acid and lamotrigine–solvent interactions are observed in all three structures and they thereby exhibit isostructurality. The DMF solvent extends the lamotrigine–lamotrigine dimers into a pseudo‐quadruple hydrogen‐bonding motif.     

Molecular Recognition Based on Roof-shaped Diol Hosts. X-Ray Crystal Structures of Inclusion Compounds with Methanol, Pyridine and Toluene

Three crystalline inclusion compounds of roof-shapedtrans-11,12-bis(diaryl-hydroxymethyl)-9,10-dihydro-9,10-ethanoanthracene host molecules [where aryl is 4-methyl-phenyl (3) or4-t-butylphenyl (4)] have been studied by X-ray diffraction.The crystals of both the 3methanol (2 : 1) [a = 10.755(1),b = 11.571(1), c = 14.697(2) Å, = 75.12(1), = 89.67(1), = 87.13(1) °] and the 4-pyridine (2 : 3) compounds[a = 14.045(3), b = 14.366(3), c = 15.607(3) Å, = 91.62(1), = 103.65(1) and =116.05(1)°] are triclinic (P–1),while the 3toluene (1 : 1) complex has orthorhombic (Fddd) symmetry [a = 16.041(1), b = 25.008(1), c = 40.440(4) Å]. The host–guest interactions in both triclinic crystals are characterised by hydrogen bonds, with different patterns however. The determined crystal structures indicate a compromise between the requirement of hydrogen bonding on the one hand and close packing on the other. The highly symmetrical host framework in the toluene (1 : 1) complex of 3 seems to be the result of shape recognition, although atendency towards weak (C_methyl)H _arylinteractions [C_methyl = 3.533(7) and 3.674(6) Å] between the hosts was observed. The present roof-shaped diol hosts give excellent examples of molecular recognition by exhibiting two significantly different conformations, mostly depending on the proton donor/acceptor ability of the guest component. (O)H O intramolecular bonding between the two alcoholic groups characterises the so-called active form, whereas weaker (O)H and interactions stabilise the `inactive'conformation.     

Three isostructural solvates of a tetrahydrofurochromenone derivative

Isostructurality is more likely to occur in multicomponent systems. In this context, three closely related solvates were crystallized, namely, benzene (C₂₇H₂₁BrO₆·C₆H₆), toluene (C₂₇H₂₁BrO₆·C₇H₈) and xylene (C₂₇H₂₁BrO₆·C₈H₁₀) with methyl 3a‐acetyl‐3‐(4‐bromophenyl)‐4‐oxo‐1‐phenyl‐3,3a,4,9b‐tetrahydro‐1H‐furo[3,4‐c ]chromene‐1‐carboxylate, and their crystal structures determined. All three structures belong to the same space group (P ) and display similar unit‐cell dimensions and conformations, as well as isostructural crystal packings. The isostructurality is confirmed by unit‐cell and isostructural similarity indices. In each solvate, weak C—H…O and C—H…π interactions extend the molecules into two‐dimensional networks, which are further linked by C—H…Br and Br…Br interactions into three‐dimensional networks. The conformation of the core molecule is predominantly responsible for governing the isostructurality.     

Crystal Structures and Packing of 2,4,6-tris(4-Fluorophenoxy)-1,3,5-triazine and 2,4,6-tris(3,4-Dimethylphenoxy)-1,3,5-triazine. New Materials for Octupolar Nonlinear Optics

The crystal structures and packing of 2,4,6-tris(4-fluorophenoxy)-1,3,5-triazine and 2,4,6-tris(3,4-dimethylphenoxy)-1,3,5-triazine are discussed. These structures have been determined as a continuation of a series of octupolar NLO materials we have been investigating. The crystal structures are characterized by C–H...F and C–H... hydrogen bonds, respectively. A characteristic of these triazine structures is the presence of dimeric Piedfort Units (PU) that are extended into more elaborate two-dimensional (2-D) networks. The structure of the fluoro derivative is compared with that of the corresponding unsubstituted and chloro/bromo-substituted derivatives. The structure of the dimethyl triazine is compared with that of the corresponding 4-methyl derivative. The noncentrosymmetric nature of the dimethyl derivative was confirmed by a powder SHG signal at 1.064 m of the order of 0.5 × KDP. Interestingly, the dimethyl derivative studied here is isostructural with the corresponding 4-methyl triazine. This H/Me isostructurality is shown to be an uncommon phenomenon by an analysis with the CSD.     

Thermal studies of solvent exchange in isostructural solvates of a tetroxoprim-sulfametrole complex

Isostructural solvates of the 1:1 molecular complex between the antibacterial drugs tetroxoprim (TXP) and sulfametrole (SMTR) with formulae TXP·SMTR·CH₃OH (I), TXP·SMTR·C₂H₅OH (II) and TXP·SMTR·H₂O (III), were investigated to establish their propensity for guest exchange. Separate exposure of powdered (I), (II) and (III) to a saturated atmosphere of each solvent of the complementary solvate pair at ambient temperature resulted in reversible solvent exchange in all cases. DSC and TG were the methods of choice for monitoring the exchange processes since (I)-(III) have distinct onset temperatures of desolvation and characteristic mass losses. Interpretation of the results in terms of the known locations of the solvent molecules in crystals of (I)-(III) led to the conclusion that solvent exchange probably proceeds by a co-operative mechanism involving material transport through channels while the common host framework is maintained. This revised version was published online in July 2006 with corrections to the Cover Date.     

Intermolecular interactions and disorder in six isostructural celecoxib solvates

Six isostructural crystalline solvates of the active pharmaceutical ingredient celecoxib {4‐[5‐(4‐methylphenyl)‐3‐(trifluoromethyl)pyrazol‐1‐yl]benzenesulfonamide; C₁₇H₁₄F₃N₃O₂S} are described, containing dimethylformamide (DMF, C₃H₇NO, 1 ), dimethylacetamide (DMA, C₄H₉NO, 2 ), N‐methylpyrrolidin‐2‐one (NMP, C₅H₉NO, 3 ), tetramethylurea (TMU, C₅H₁₂N₂O, 4 ), 1,3‐dimethyl‐3,4,5,6‐tetrahydropyrimidin‐2(1H)‐one (DMPU, C₆H₁₂N₂O, 5 ) or dimethyl sulfoxide (DMSO, C₂H₆OS, 6 ). The host celecoxib structure contains one‐dimensional channel voids accommodating the solvent molecules, which accept hydrogen bonds from the NH₂ groups of two celecoxib molecules. The solvent binding sites have local twofold rotation symmetry, which is consistent with the point symmetry of the solvent molecule in 4 and 5 , but introduces orientational disorder for the solvent molecules in 1 , 2 , 3 and 6 . Despite the isostructurality of 1 – 6 , the unit‐cell volume and solvent‐accessible void space show significant variation. In particular, 4 and 5 show an enlarged and skewed unit cell, which can be attributed to a specific interaction between an N—CH₃ group in the solvent molecule and the toluene group of celecoxib. Intermolecular interaction energies calculated using the PIXEL method show that the total interaction energy between the celecoxib and solvent molecules is broadly correlated with the molecular volume of the solvent, except in 6 , where the increased polarity of the S=O bond leads to greater overall stabilization compared to the similarly‐sized DMF molecule in 1 . In the structures showing disorder, the most stable orientations of the solvent molecules make C—H…O contacts to the S=O groups of celecoxib.     

Inclusion of the Antidepressant Paroxetine in β-cyclodextrin

The X-ray structure and thermal stability of a -cyclodextrin inclusion complex of the antidepressant paroxetine [(3S-trans)-3-[(1,3-benzodioxol-5-yloxy)methyl]-4-(4-fluorophenyl)piperidine], with the formula ( -cyclodextrin)₂...paroxetine...28H₂O, are reported. On heating, the crystals dehydrate in two stages and begin to decompose from approximately 270 °C. An X-ray diffraction study at 173K showed that the complex crystallizes in the monoclinic system, space group P2₁ with a = 15.2262(3), b = 31.4771(1), c = 15.6739(1) Å, = 104.320(1)° and Z = 2 formula units. Refinement on F² converged at R1 = 0.066, wR₂ = 0.182 (21478 reflections). On encapsulation within a head-to-head -cyclodextrin dimer, the paroxetine molecule adopts an unusual `hairpin' conformation, stabilised by intramolecular ... interaction between the phenyl rings. The guest piperidine ring is located at the primary face of one host molecule of the dimer while the fluorophenyl and benzodioxole moieties respectively occupy the dimer interfacial region and the cavity of the second host molecule. Experimental and computed X-ray powder diffraction patterns for the complex are also reported. The mode of stacking of the dimeric complex units is shown to be one of at least three distinct variants which can be identified for -cyclodextrin complexes with similar unit cell dimensions and crystallizing in the same space group.     

X-ray crystal structures and isostructurality calculation of calix[4]arenes with lower rim propyl and carboxylic acid or mixed carboxylic acid and ester substituents involving solvent complexes with methanol and ethanol

X-ray crystal structures of two calix[4]arenes are reported. They feature aside from two distal n-propyl units, two ethyl acetate or mixed ethyl acetate and acetic acid groups as the characteristic substituents of the lower rim hydroxylic hydrogens. The structures are compared by making use of isostructurality calculations. In case of the semi-ester, solvates with methanol and ethanol as the guest solvents are involved. The carboxy function of the semi-ester does not form a dimer but an intramolecular hydrogen bond to a propoxy group. The solvates can be described as isostructural in spite of the different solvent molecules. Original Russian Text Copyright ? 2009 by T. Gruber, P. Bombicz, W. Seichter, and E. Weber The text was submitted by the authors in English. Zhurnal Strukturnoi Khimii, Vol. 50, No. 3, pp. 544–552, May–June, 2009.