Pseudopolymorphs of chelidamic acid and its dimethyl ester

Different tautomeric and zwitterionic forms of chelidamic acid (4‐hydroxypyridine‐2,6‐dicarboxylic acid) are present in the crystal structures of chelidamic acid methanol monosolvate, C₇H₅NO₅·CH₄O, (Ia), dimethylammonium chelidamate (dimethylammonium 6‐carboxy‐4‐hydroxypyridine‐2‐carboxylate), C₂H₈N⁺·C₇H₄NO₅⁻, (Ib), and chelidamic acid dimethyl sulfoxide monosolvate, C₇H₅NO₅·C₂H₆OS, (Ic). While the zwitterionic pyridinium carboxylate in (Ia) can be explained from the pK_a values, a (partially) deprotonated hydroxy group in the presence of a neutral carboxy group, as observed in (Ib) and (Ic), is unexpected. In (Ib), there are two formula units in the asymmetric unit with the chelidamic acid entities connected by a symmetric O—H...O hydrogen bond. Also, crystals of chelidamic acid dimethyl ester (dimethyl 4‐hydroxypyridine‐2,6‐dicarboxylate) were obtained as a monohydrate, C₉H₉NO₅·H₂O, (IIa), and as a solvent‐free modification, in which both ester molecules adopt the hydroxypyridine form. In (IIa), the solvent water molecule stabilizes the synperiplanar conformation of both carbonyl O atoms with respect to the pyridine N atom by two O—H...O hydrogen bonds, whereas an antiperiplanar arrangement is observed in the water‐free structure. A database study and ab initio energy calculations help to compare the stabilities of the various ester conformations.     

Five N′‐benzylidene‐N‐methylpyrazine‐2‐carbohydrazides

The compounds N′‐benzylidene‐N‐methylpyrazine‐2‐carbohydrazide, C₁₃H₁₂N₄O, (IIa), N′‐(2‐methoxybenzylidene)‐N‐methylpyrazine‐2‐carbohydrazide, C₁₄H₁₄N₄O₂, (IIb), N′‐(4‐cyanobenzylidene)‐N‐methylpyrazine‐2‐carbohydrazide dihydrate, C₁₄H₁₁N₅O·2H₂O, (IIc), N‐methyl‐N′‐(2‐nitrobenzylidene)pyrazine‐2‐carbohydrazide, C₁₃H₁₁N₅O₃, (IId), and N‐methyl‐N′‐(4‐nitrobenzylidene)pyrazine‐2‐carbohydrazide, C₁₃H₁₁N₅O₃, (IIe), have dihedral angles between the pyrazine rings and the benzene rings in the range 55–78°. These methylated pyrazine‐2‐carbohydrazides have supramolecular structures which are formed by weak C—H...O/N hydrogen bonds, with the exception of (IIc) which is hydrated. There are π–π stacking interactions in all five compounds. Three of these structures are compared with their nonmethylated counterparts, which have dihedral angles between the pyrazine rings and the benzene rings in the range 0–6°.     

Synthesis and crystal structures of some bis(3‐methyl‐1H‐indol‐2‐yl)(salicyl)methanes

Four 2,2′‐bisindolylmethanes (BIMs), a useful class of polyindolyl species joined to a central carbon, were synthesized using salicylaldehyde derivatives and simple acid catalysis; these are 2‐[bis(3‐methyl‐1H‐indol‐2‐yl)methyl]‐6‐methylphenol, (IIa), 2‐[bis(3‐methyl‐1H‐indol‐2‐yl)methyl]‐4,6‐dichlorophenol, (IIb), 2‐[bis(3‐methyl‐1H‐indol‐2‐yl)methyl]‐4‐nitrophenol, (IIc), and 2‐[bis(3‐methyl‐1H‐indol‐2‐yl)methyl]‐4,6‐di‐tert‐butylphenol, (IId). BIMs (IIa) and (IIb) were characterized crystallographically as the dimethyl sulfoxide (DMSO) disolvates, i.e. C₂₆H₂₄N₂O·2C₂H₆OS and C₂₅H₂₀Cl₂N₂O·2C₂H₆OS, respectively. Both form strikingly similar one‐dimensional hydrogen‐bonding chain motifs with the DMSO solvent molecules. BIM (IIa) packs into double layers of chains whose orientations alternate every double layer, while (IIb) forms more simply packed chains along the a axis. BIM (IIa) has a remarkably long c axis.     

Three anilides of 2,2′‐thiodibenzoic acid

The structures of N,N′‐bis(2‐methylphenyl)‐2,2′‐thiodibenzamide, C₂₈H₂₄N₂O₂S, (Ia), N,N′‐bis(2‐ethylphenyl)‐2,2′‐thiodibenzamide, C₃₀H₂₈N₂O₂S, (Ib), and N,N′‐bis(2‐bromophenyl)‐2,2′‐thiodibenzamide, C₂₆H₁₈Br₂N₂O₂S, (Ic), are compared with each other. For the 19 atoms of the consistent thiodibenzamide core, the r.m.s. deviations of the molecules in pairs are 0.29, 0.90 and 0.80 Å for (Ia)/(Ib), (Ia)/(Ic) and (Ib)/(Ic), respectively. The conformations of the central parts of molecules (Ia) and (Ib) are similar due to an intramolecular N—H...O hydrogen‐bonding interaction. The molecules of (Ia) are further linked into infinite chains along the c axis by intermolecular N—H...O interactions, whereas the molecules of (Ib) are linked into chains along b by an intermolecular N—H...π contact. The conformation of (Ic) is quite different from those of (Ia) and (Ib), since there is no intramolecular N—H...O hydrogen bond, but instead there is a possible intramolecular N—H...Br hydrogen bond. The molecules are linked into chains along c by intermolecular N—H...O hydrogen bonds.     

Pseudopolymorphs of 2,6‐diaminopyrimidin‐4‐one and 2‐amino‐6‐methylpyrimidin‐4‐one: one or two tautomers present in the same crystal

The derivatives of pyrimidin‐4‐one can adopt either a 1H‐ or a 3H‐tautomeric form, which affects the hydrogen‐bonding interactions in cocrystals with compounds containing complementary functional groups. In order to study their tautomeric preferences, we crystallized 2,6‐diaminopyrimidin‐4‐one and 2‐amino‐6‐methylpyrimidin‐4‐one. During various crystallization attempts, four structures of 2,6‐diaminopyrimidin‐4‐one were obtained, namely solvent‐free 2,6‐diaminopyrimidin‐4‐one, C₄H₆N₄O, (I), 2,6‐diaminopyrimidin‐4‐one–dimethylformamide–water (3/4/1), C₄H₆N₄O·1.33C₃H₇NO·0.33H₂O, (Ia), 2,6‐diaminopyrimidin‐4‐one dimethylacetamide monosolvate, C₄H₆N₄O·C₄H₉NO, (Ib), and 2,6‐diaminopyrimidin‐4‐one–N‐methylpyrrolidin‐2‐one (3/2), C₄H₆N₄O·1.5C₅H₉NO, (Ic). The 2,6‐diaminopyrimidin‐4‐one molecules exist only as 3H‐tautomers. They form ribbons characterized by R²₂(8) hydrogen‐bonding interactions, which are further connected to form three‐dimensional networks. An intermolecular N—H...N interaction between amine groups is observed only in (I). This might be the reason for the pyramidalization of the amine group. Crystallization experiments on 2‐amino‐6‐methylpyrimidin‐4‐one yielded two isostructural pseudopolymorphs, namely 2‐amino‐6‐methylpyrimidin‐4(3H)‐one–2‐amino‐6‐methylpyrimidin‐4(1H)‐one–dimethylacetamide (1/1/1), C₅H₇N₃O·C₅H₇N₃O·C₄H₉NO, (IIa), and 2‐amino‐6‐methylpyrimidin‐4(3H)‐one–2‐amino‐6‐methylpyrimidin‐4(1H)‐one–N‐methylpyrrolidin‐2‐one (1/1/1), C₅H₇N₃O·C₅H₇N₃O·C₅H₉NO, (IIb). In both structures, a 1:1 mixture of 1H‐ and 3H‐tautomers is present, which are linked by three hydrogen bonds similar to a Watson–Crick C–G base pair.     

Three new fluorinated N‐phenyl‐substituted pentacyclic ethanoanthracenedicarboximides

Diels–Alder reaction between maleimides featuring 3,5‐di‐, 2,4,6‐tri‐ and pentafluorinated N‐phenyl substituents and anthracene yields the corresponding pentacyclic ethanoanthracenedicarboximide compounds, namely N‐(3,5‐difluorophenyl)‐9,10‐dihydro‐9,10‐ethanoanthracene‐11,12‐dicarboximide, C₂₄H₁₅F₂NO₂, (IIa), N‐(2,4,6‐trifluorophenyl)‐9,10‐dihydro‐9,10‐ethanoanthracene‐11,12‐dicarboximide, C₂₄H₁₄F₃NO₂, (IIb), N‐(2,3,4,5,6‐pentafluorophenyl)‐9,10‐dihydro‐9,10‐ethanoanthracene‐11,12‐dicarboximide, C₂₄H₁₂F₅NO₂, (IIc). The crystal structures of (IIa)–(IIc) reveal an expected molecular geometry with a `V'‐shape of the anthracene‐derived tricyclic moiety. The crystal packings of (IIa) and (IIb) are dominated by π–π and C—H...O/F interactions, while F...F and C—H...π contacts are absent. In contrast, (IIc) shows F...F and C—H...O/F contacts, but no π‐involved contacts of relevance.     

Channel‐forming solvates of 6‐chloro‐2,5‐dihydroxypyridine and its solvent‐free tautomer 6‐chloro‐5‐hydroxy‐2‐pyridone

On crystallization from CHCl₃, CCl₄, CH₂ClCH₂Cl and CHCl₂CHCl₂, 6‐chloro‐5‐hydroxy‐2‐pyridone, C₅H₄ClNO₂, (I), undergoes a tautomeric rearrangement to 6‐chloro‐2,5‐dihydroxypyridine, (II). The resulting crystals, viz. 6‐chloro‐2,5‐dihydroxypyridine chloroform 0.125‐solvate, C₅H₄ClNO₂·0.125CHCl₃, (IIa), 6‐chloro‐2,5‐dihydroxypyridine carbon tetrachloride 0.125‐solvate, C₅H₄ClNO₂.·0.125CCl₄, (IIb), 6‐chloro‐2,5‐dihydroxypyridine 1,2‐dichloroethane solvate, C₅H₄ClNO₂·C₂H₄Cl₂, (IIc), and 6‐chloro‐2,5‐dihydroxypyridine 1,1,2,2‐tetrachloroethane solvate, C₅H₄ClNO₂·C₂H₂Cl₄, (IId), have I4₁/a symmetry, and incorporate extensively disordered solvent in channels that run the length of the c axis. Upon gentle heating to 378 K in vacuo, these crystals sublime to form solvent‐free crystals with P2₁/n symmetry that are exclusively the pyridone tautomer, (I). In these sublimed pyridone crystals, inversion‐related molecules form R²₂(8) dimers via pairs of N—H...O hydrogen bonds. The dimers are linked by O—H...O hydrogen bonds into R⁴₆(28) motifs, which join to form pleated sheets that stack along the a axis. In the channel‐containing pyridine solvate crystals, viz. (IIa)–(IId), two independent host molecules form an R²₂(8) dimer via a pair of O—H...N hydrogen bonds. One molecule is further linked by O—H...O hydrogen bonds to two 4₁ screw‐related equivalents to form a helical motif parallel to the c axis. The other independent molecule is O—H...O hydrogen bonded to two related equivalents to form tetrameric R⁴₄(28) rings. The dimers are π–π stacked with inversion‐related dimers, which in turn stack the R⁴₄(28) rings along c to form continuous solvent‐accessible channels. CHCl₃, CCl₄, CH₂ClCH₂Cl and CHCl₂CHCl₂ solvent molecules are able to occupy these channels but are disordered by virtue of the site symmetry within the channels.     

Bis(2,5‐dimethoxy‐4‐methylphenyl)methane and bis(2,5‐dimethoxy‐3,4,6‐trimethylphenyl)methane

Bis(2,5‐di­methoxy‐4‐methyl­phenyl)­methane, C₁₉H₂₄O₄, (IIa), was obtained and characterized as a minor product from the reaction of tolu­hydro­quinone di­methyl ether (1,4‐dimethoxy‐2‐methylbenzene) with N‐(hydroxy­methyl)­tri­fluoro­acet­amide. Similarly, bis(2,5‐di­methoxy‐3,4,6‐tri­methyl­phenyl)­methane, C₂₃H₃₂O₄, (IIb), was prepared from the corresponding reaction of tri­methyl­hydro­quinone di­methyl ether (2,5‐dimethoxy‐1,3,4‐trimethylbenzene). The mol­ecules of (IIa) and (IIb) each lie on a twofold axis passing through the methyl­ene group. The dihedral angle between the planar phenyl rings is 73.4 (1)° in (IIa) and 77.9 (1)° in (IIb). The external bond angles around the bridging methyl­ene group are 116.6 (2) and 117.3 (2)° for (IIa) and (IIb), respectively. In (IIa), the methoxy substituents lie in the plane of the ring and are conjugated with the aromatic system, whereas in (IIb), they are almost perpendicular to the phenyl ring and are positioned on opposite sides.     

catena‐Poly[[[(benzene‐1,3,5‐tricarboxylic acid)(1,10‐phenanthroline)cadmium(II)]‐μ‐oxalato] 1H‐benzotriazole solvate monohydrate]

In the title compound, [Cd(C₂O₄)(C₁₂H₈N₂)(C₉H₆O₆)]·C₆H₅N₃·H₂O, the Cd^II atom has a distorted pentagonal–bipyramidal geometry, defined by two N atoms and five O atoms from bidentate 1,10‐phenanthroline ligands, oxalate ligands and benzene‐1,3,5‐tricarboxylic acid ligands. The oxalate ligands in the asymmetric unit possess inversion symmetry. The triazole molecule is not coordinated to the Cd atom. The structure of the title compound features a one‐dimensional chain running along the crystallographic a axis, and a three‐dimensional supramolecular network is formed via aromatic π–π interactions and hydrogen‐bonding interactions.     

Isotype Borophosphate MII(C2H10N2)[B2P3O12(OH)] (MII = Mg,Mn, Fe,Ni, Cu,Zn): Verbindungen mit Tetraeder‐Schichtverbänden

Isotypic Borophosphates M^II(C₂H₁₀N₂)[B₂P₃O₁₂(OH)] (M^II = Mg, Mn, Fe, Ni, Cu, Zn): Compounds containing Tetrahedral Layers The isotypic compounds M^II(C₂H₁₀N₂) · [B₂P₃O₁₂(OH)] (M^II = Mg, Mn, Fe, Ni, Cu, Zn) were prepared under hydrothermal conditions (T = 170 °C) from mixtures of the metal chloride (chloride hydrate, resp.), Ethylenediamine, H₃BO₃ and H₃PO₄. The orthorhombic crystal structures (Pbca, No. 61, Z = 8) were determined by X‐ray single crystal methods (Mg(C₂H₁₀N₂)[B₂P₃O₁₂(OH)]: a = 936.81(2) pm, b = 1221.86(3) pm, c = 2089.28(5) pm) and Rietveld‐methods (M^II = Mn: a = 931.91(4) pm, b = 1234.26(4) pm, c = 2129.75(7) pm, Fe: a = 935.1(3) pm, b = 1224.8(3) pm, c = 2088.0(6) pm, Ni: a = 939.99(3) pm, b = 1221.29(3) pm, c = 2074.05(7) pm, Cu: a = 941.38(3) pm, b = 1198.02(3) pm, c = 2110.01(6) pm, Zn: a = 935.06(2) pm, b = 1221.33(2) pm, c = 2094.39(4) pm), respectively. The anionic part of the structure contains tetrahedral layers, consisting of three‐ and nine‐membered rings. The M^II‐ions are in a distorted octahedral or tetragonal‐bipyramidal [4 + 2] (copper) coordination formed by oxygen functions of the tetrahedral layers. The resulting three‐dimensional structure contains channels running along [010]. Protonated Ethylenediamine ions are fixed within the channels by hydrogen bonds.     

Probing the supramolecular interaction synthons of 1‐benzofuran‐2,3‐dicarboxylic acid in its monoanionic form

1‐Benzofuran‐2,3‐dicarboxylic acid (C₁₀H₆O₅) is a dicarboxylic acid ligand which can readily engage in organometallic complexes with various metal ions. This ligand is characterized by an intramolecular hydrogen bond between the two carboxyl residues, and, as a monoanionic species, readily forms supramolecular adducts with different organic and inorganic cations. These are a 1:1 adduct with the dimethylammonium cation, namely dimethylammonium 3‐carboxy‐1‐benzofuran‐2‐carboxylate, C₂H₈N⁺·C₁₀H₅O₅⁻, (I), a 2:1 complex with Cu²⁺ ions in which four neutral imidazole molecules also coordinate the metal atom, namely bis(3‐carboxy‐1‐benzofuran‐2‐carboxylato‐κO³)tetrakis(1H‐imidazole‐κN³)copper(II), [Cu(C₁₀H₅O₅)₂(C₃H₄N₂)₄], (II), and a 4:1 adduct with [La(H₂O)₇]³⁺ ions, namely heptaaquabis(3‐carboxy‐1‐benzofuran‐2‐carboxylato‐κO³)lanthanum 3‐carboxy‐1‐benzofuran‐2‐carboxylate 1‐benzofuran‐2,3‐dicarboxylic acid solvate tetrahydrate, [La(C₁₀H₅O₅)₂(H₂O)₇](C₁₀H₅O₅)·C₁₀H₆O₅·4H₂O, (III). In the crystal structure, complex (II) resides on inversion centres, while complex (III) resides on axes of twofold rotation. The crystal packing in all three structures reveals π–π stacking interactions between the planar aromatic benzofuran residues, as well as hydrogen bonding between the components. The significance of this study lies in the first crystallographic characterization of the title framework, which consistently exhibits the presence of an intramolecular hydrogen bond and a consequent monoanionic‐only nature. It shows further that the anion can coordinate readily to metal cations as a ligand, as well as acting as a monovalent counter‐ion. Finally, the aromaticity of the flat benzofuran residue provides an additional supramolecular synthon that directs and facilitates the crystal packing of compounds (I)–(III).     

Competing intermolecular interactions in some `bridge‐flipped' isomeric phenylhydrazones

To examine the roles of competing intermolecular interactions in differentiating the molecular packing arrangements of some isomeric phenylhydrazones from each other, the crystal structures of five nitrile–halogen substituted phenylhydrazones and two nitro–halogen substituted phenylhydrazones have been determined and are described here: (E)‐4‐cyanobenzaldehyde 4‐chlorophenylhydrazone, C₁₄H₁₀ClN₃, (Ia); (E)‐4‐cyanobenzaldehyde 4‐bromophenylhydrazone, C₁₄H₁₀BrN₃, (Ib); (E)‐4‐cyanobenzaldehyde 4‐iodophenylhydrazone, C₁₄H₁₀IN₃, (Ic); (E)‐4‐bromobenzaldehyde 4‐cyanophenylhydrazone, C₁₄H₁₀BrN₃, (IIb); (E)‐4‐iodobenzaldehyde 4‐cyanophenylhydrazone, C₁₄H₁₀IN₃, (IIc); (E)‐4‐chlorobenzaldehyde 4‐nitrophenylhydrazone, C₁₃H₁₀ClN₃O₂, (III); and (E)‐4‐nitrobenzaldehyde 4‐chlorophenylhydrazone, C₁₃H₁₀ClN₃O₂, (IV). Both (Ia) and (Ib) are disordered (less than 7% of the molecules have the minor orientation in each structure). Pairs (Ia)/(Ib) and (IIb)/(IIc), related by a halogen exchange, are isomorphous, but none of the `bridge‐flipped' isomeric pairs, viz. (Ib)/(IIb), (Ic)/(IIc) or (III)/(IV), is isomorphous. In the nitrile–halogen structures (Ia)–(Ic) and (IIb)–(IIc), only the bridge N—H group and not the bridge C—H group acts as a hydrogen‐bond donor to the nitrile group, but in the nitro–halogen structures (III) (with Z′ = 2) and (IV), both the bridge N—H group and the bridge C—H group interact with the nitro group as hydrogen‐bond donors, albeit via different motifs. The occurrence here of the bridge C—H contact with a hydrogen‐bond acceptor suggests the possibility that other pairs of `bridge‐flipped' isomeric phenylhydrazones may prove to be isomorphous, regardless of the change from isomer to isomer in the position of the N—H group within the bridge.     

2‐Ammonio‐5‐chloro‐4‐methylbenzenesulfonate,its 1‐methyl‐2‐pyrrolidone and dimethyl sulfoxide monosolvates and a corrected structure of 2,2′‐(1,4‐phenylene)di(4,5‐dihydroimidazolium) bis(4‐aminobenzenesulfonate) dihydrate

2‐Ammonio‐5‐chloro‐4‐methylbenzenesulfonate, C₇H₈ClNO₃S, (Ia), is an intermediate in the synthesis of lake red azo pigments. The present structure determination from single‐crystal data confirms the results of a previous powder diffraction determination [Bekö, Thoms, Brüning, Alig, van de Streek, Lakatos, Glaubitz & Schmidt (2010). Z. Kristallogr. 225 , 382–387]. The zwitterionic tautomeric form is confirmed. During a polymorph screening, two additional pseudopolymorphs were obtained, viz. 2‐ammonio‐5‐chloro‐4‐methylbenzenesulfonate 1‐methyl‐2‐pyrrolidone monosolvate, C₇H₈ClNO₃S·C₅H₉NO, (Ib), and 2‐ammonio‐5‐chloro‐4‐methylbenzenesulfonate dimethyl sulfoxide monosolvate, C₇H₈ClNO₃S·C₂H₆OS, (Ic). The molecules of (Ib) have crystallographic m symmetry. The 1‐methyl‐2‐pyrrolidone solvent molecule has an envelope conformation and is disordered around the mirror plane. The structure shows hydrogen‐bonded ladders of molecules [graph‐set notation C₂²(6)R₂²(12)] in the [010] direction. The benzene groups of adjacent ladders are also stacked in this direction. A different type of hydrogen‐bonded ladder [graph‐set notation C(6)R₂²(4)R₄⁴(12)] occurs in (Ic). In (Ia), (Ib) and (Ic), the molecules correspond to the zwitterionic tautomer. The structure of the cocrystal of 4‐aminobenzenesulfonic acid with 1,4‐bis(4,5‐dihydroimidazol‐2‐yl)benzene [Shang, Ren, Wang, Lu & Yang (2009). Acta Cryst. E 65 , o2221–o2222] is corrected; it actually contains 4‐aminobenzenesulfonate anions and 2,2′‐(1,4‐phenylene)di(dihydroimidazolium) dications, i.e. 2,2′‐(1,4‐phenylene)di(4,5‐dihydroimidazolium) bis(4‐aminobenzenesulfonate) dihydrate, C₁₂H₁₆N₄²⁺·2C₆H₆NO₃S⁻·2H₂O. Hence, all known structures of aminobenzenesulfonic acid complexes contain ionic or zwitterionic molecules; there is no known structure with a neutral aminobenzenesulfonic acid molecule.     

Conformations and resulting hydrogen‐bonded networks of hydrogen {phosphono[(pyridin‐1‐ium‐3‐yl)amino]methyl}phosphonate and related 2‐chloro and 6‐chloro derivatives

In the crystal structures of the conformational isomers hydrogen {phosphono[(pyridin‐1‐ium‐3‐yl)amino]methyl}phosphonate monohydrate (pro‐E), C₆H₁₀N₂O₆P₂·H₂O, (Ia), and hydrogen {phosphono[(pyridin‐1‐ium‐3‐yl)amino]methyl}phosphonate (pro‐Z), C₆H₁₀N₂O₆P₂, (Ib), the related hydrogen {[(2‐chloropyridin‐1‐ium‐3‐yl)amino](phosphono)methyl}phosphonate (pro‐E), C₆H₉ClN₂O₆P₂, (II), and the salt bis(6‐chloropyridin‐3‐aminium) [hydrogen bis({[2‐chloropyridin‐1‐ium‐3‐yl(0.5+)]amino}methylenediphosphonate)] (pro‐Z), 2C₅H₆ClN₂⁺·C₁₂H₁₆Cl₂N₄O₁₂P₄²⁻, (III), chain–chain interactions involving phosphono (–PO₃H₂) and phosphonate (–PO₃H⁻) groups are dominant in determining the crystal packing. The crystals of (Ia) and (III) comprise similar ribbons, which are held together by N—H...O interactions, by water‐ or cation‐mediated contacts, and by π–π interactions between the aromatic rings of adjacent zwitterions in (Ia), and those of the cations and anions in (III). The crystals of (Ib) and (II) have a layered architecture: the former exhibits highly corrugated monolayers perpendicular to the [100] direction, while in the latter, flat bilayers parallel to the (001) plane are formed. In both (Ib) and (II), the interlayer contacts are realised through N—H...O hydrogen bonds and weak C—H...O interactions involving aromatic C atoms.     

A concise synthesis of a highly substituted 6‐(1H‐benzimidazol‐1‐yl)‐5‐nitrosopyrimidin‐2‐amine: synthetic sequence and the molecular and supramolecular structures of one product and two intermediates

A concise and efficient synthesis of 6‐benzimidazolyl‐5‐nitrosopyrimidines has been developed using Schiff base‐type intermediates derived from N⁴‐(2‐aminophenyl)‐6‐methoxy‐5‐nitrosopyrimidine‐2,4‐diamine. 6‐Methoxy‐N⁴‐{2‐[(4‐methylbenzylidene)amino]phenyl}‐5‐nitrosopyrimidine‐2,4‐diamine, (I), and N⁴‐{2‐[(ethoxymethylidene)amino]phenyl}‐6‐methoxy‐5‐nitrosopyrimidine‐2,4‐diamine, (III), both crystallize from dimethyl sulfoxide solution as the 1:1 solvates C₁₉H₁₈N₆O₂·C₂H₆OS, (Ia), and C₁₄H₁₆N₆O₃·C₂H₆OS, (IIIa), respectively. The interatomic distances in these intermediates indicate significant electronic polarization within the substituted pyrimidine system. In each of (Ia) and (IIIa), intermolecular N—H…O hydrogen bonds generate centrosymmetric four‐molecule aggregates. Oxidative ring closure of intermediate (I), effected using ammonium hexanitratocerate(IV), produced 4‐methoxy‐6‐[2‐(4‐methylphenyl‐1H‐benzimidazol‐1‐yl]‐5‐nitrosopyrimidin‐2‐amine, C₁₉H₁₆N₆O₂, (II) [Cobo et al. (2018). Private communication (CCDC 1830889). CCDC, Cambridge, England], where the extent of electronic polarization is much less than in (Ia) and (IIIa). A combination of N—H…N and C—H…O hydrogen bonds links the molecules of (II) into complex sheets.     

Tris(1,10‐phenanthroline‐κ2N,N′)iron(II) bis(2,4,5‐tricarboxybenzoate) monohydrate and tris(2,2′‐bipyridine‐κ2N,N′)iron(II) 2,5‐dicarboxybenzene‐1,4‐dicarboxylate–benzene‐1,2,4,5‐tetracarboxylic acid–water (1/1/2)

The title compounds, tris(1,10‐phenanthroline‐κ²N,N′)iron(II) bis(2,4,5‐tricarboxybenzoate) monohydrate, [Fe(C₁₂H₈N₂)₃](C₁₀H₅O₈)₂·H₂O, (I), and tris(2,2′‐bipyridine‐κ²N,N′)iron(II) 2,5‐dicarboxybenzene‐1,4‐dicarboxylate–benzene‐1,2,4,5‐tetracarboxylic acid–water (1/1/2), [Fe(C₁₀H₈N₂)₃](C₁₀H₄O₈)·C₁₀H₆O₈·2H₂O, (II), were obtained during an attempt to synthesize a mixed‐ligand complex of Fe^II with an N‐containing ligand and benzene‐1,2,4,5‐tetracarboxylic acid via a solvothermal reaction. In both mononuclear complexes, each Fe^II metal ion is six‐coordinated in a distorted octahedral manner by six N atoms from three chelating 1,10‐phenanthroline or 2,2′‐bipyridine ligands. In compound (I), the Fe^II atom lies on a twofold axis in the space group C2/c, whereas (II) crystallizes in the space group P2₁/n. In both compounds, the uncoordinated carboxylate anions and water molecules are linked by typical O—H...O hydrogen bonds, generating extensive three‐dimensional hydrogen‐bond networks which surround the cations.     

Five pseudopolymorphs and a cocrystal of nitrofurantoin

The antibiotic nitrofurantoin {systematic name: (E)‐1‐[(5‐nitro‐2‐furyl)methylideneamino]imidazolidine‐2,4‐dione} is not only used for the treatment of urinary tract infections, but also illegally applied as an animal food additive. Since derivatives of 2,6‐diaminopyridine might serve as artificial receptors for its recognition, we crystallized one potential drug–receptor complex, nitrofurantoin–2,6‐diacetamidopyridine (1/1), C₈H₆N₄O₅·C₉H₁₁N₃O₂, (I·II). It is characterized by one N—H...N and two N—H...O hydrogen bonds and confirms a previous NMR study. During the crystallization screening, several new pseudopolymorphs of both components were obtained, namely a nitrofurantoin dimethyl sulfoxide monosolvate, C₈H₆N₄O₅·C₂H₆OS, (Ia), a nitrofurantoin dimethyl sulfoxide hemisolvate, C₈H₆N₄O₅·0.5C₂H₆OS, (Ib), two nitrofurantoin dimethylacetamide monosolvates, C₈H₆N₄O₅·C₄H₉NO, (Ic) and (Id), and a nitrofurantoin dimethylacetamide disolvate, C₈H₆N₄O₅·2C₄H₉NO, (Ie), as well as a 2,6‐diacetamidopyridine dimethylformamide monosolvate, C₉H₁₁N₃O₂·C₃H₇NO, (IIa). Of these, (Ia), (Ic) and (Id) were formed during cocrystallization attempts with 1‐(4‐fluorophenyl)biguanide hydrochloride. Obviously nitrofurantoin prefers the higher‐energy conformation in the crystal structures, which all exhibit N—H...O and C—H...O hydrogen‐bond interactions. The latter are especially important for the crystal packing. 2,6‐Diacetamidopyridine shows some conformational flexibility depending on the hydrogen‐bond pattern.     

Three solvates of a bis‐mesoionic fluorescent yellow pigment

p‐Phenylenebis(2‐oxo‐3‐phenyl‐1,2‐dihydropyrido[1,2‐a]pyrimidin‐5‐ium‐4‐olate), C₃₄H₂₂N₄O₄, is a bis‐mesoionic yellow pigment that shows fluorescence in the solid state. During a polymorph screening, single crystals of three solvates were grown and their crystal structures determined. Solvent‐free crystals were not obtained. A solvate with N‐methylpyrrolidone (NMP) and propan‐2‐ol, C₃₄H₂₂N₄O₄·2C₅H₉NO·C₃H₈O, (Ia), and an NMP trisolvate, C₃₄H₂₂N₄O₄·3C₅H₉NO, (Ib), crystallize with pigment molecules on inversion centres. The NMP/propan‐2‐ol mixed solvate (Ia) forms O—H...O hydrogen bonds between the different solvent molecules. In both structures, at least one of the solvent molecules is disordered. A third solvate structure, C₃₄H₂₂N₄O₄·0.5C₅H₉NO·C₄H₁₀O, (Ic), was obtained by crystallization from NMP and butan‐1‐ol. In this case, there are two symmetry‐independent pigment molecules, both situated on inversion centres. The solvent molecules are heavily disordered and their contribution to the scattering was suppressed. This solvate displays a channel structure, whereas the other two solvates form layer structures.     

Structural effects on the solid‐state photodimerization of 2‐pyridone derivatives in inclusion compounds

The structures of six crystalline inclusion compounds between various host molecules and three guest molecules based on the 2‐pyridone skeleton are described. The six compounds are 1,1′‐biphenyl‐2,2′‐dicarboxylic acid–2‐pyridone (1/2), C₁₄H₁₀O₄·2C₅H₅NO, (I–a), 1,1′‐biphenyl‐2,2′‐dicarboxylic acid–4‐methyl‐2‐pyridone (1/2), C₁₄H₁₀O₄·2C₆H₇NO, (I–c), 1,1′‐biphenyl‐2,2′‐dicarboxylic acid–6‐methyl‐2‐pyridone (1/2), C₁₄H₁₀O₄·2C₆H₇NO, (I–d), 1,1,6,6‐tetraphenyl‐2,4‐hexadiyne‐1,6‐diol–1‐methyl‐2‐pyridone (1/2), C₃₀H₂₂O₂·2C₆H₇NO, (II–b), 1,1,6,6‐tetraphenyl‐2,4‐hexadiyne‐1,6‐diol–4‐methy‐2‐pyridone (1/2), C₃₀H₂₂O₂·2C₆H₇NO, (II–c), and 4,4′,4′′‐(ethane‐1,1,1‐triyl)triphenol–6‐methyl‐2‐pyridone–water (1/3/1), C₂₀H₁₈O₃·3C₆H₇NO·H₂O, (III–d). In two of the compounds, (I–a) and (I–d), the host molecules lie about crystallographic twofold axes. In two other compounds, (II–b) and (II–c), the host molecules lie across inversion centers. In all cases, the guest molecules are hydrogen bonded to the host molecules through O—H...O=C hydrogen bonds [the range of O...O distances is 2.543 (2)–2.843 (2) Å. The pyridone moieties form dimers through N—H...O=C hydrogen bonds in five of the compounds [the range of N...O distances is 2.763 (2)–2.968 (2) Å]. In four compounds, (I–a), (I–c), (I–d) and (II–c), the molecules are arranged in extended zigzag chains formed via host–guest hydrogen bonding. In five of the compounds, the guest molecules are arranged in parallel pairs on top of each other, related by inversion centers. However, none of these compounds underwent photodimerization in the solid state upon irradiation. In one of the crystalline compounds, (III–d), the guest molecules are arranged in stacks with one disordered molecule. The unsuccessful dimerization is attributed to the large interatomic distances between the potentially reactive atoms [the range of distances is 4.027 (4)–4.865 (4) Å] and to the bad overlap, expressed by the lateral shift between the orbitals of these atoms [the range of the shifts from perfect overlap is 1.727 (4)–3.324 (4) Å]. The bad overlap and large distances between potentially photoreactive atoms are attributed to the hydrogen‐bonding schemes, because the interactions involved in hydrogen bonding are stronger than those in π–π interactions.     

The three‐dimensional coordination polymer poly[[aqua[μ4‐2,2′‐(diazene‐1,2‐diyl)dibenzoato]lead(II)] 1,2‐bis(pyridin‐4‐yl)ethylene hemisolvate]

A novel three‐dimensional coordination polymer, {[Pb(C₁₄H₈N₂O₄)(H₂O)]·0.5C₁₂H₁₀N₂}_n, has been synthesized by hydrothermal reaction of Pb(OAc)₂·3H₂O (OAc is acetate), 2,2′‐(diazene‐1,2‐diyl)dibenzoic acid (H₂L) and 1,2‐bis(pyridin‐4‐yl)ethylene (bpe). The asymmetric unit contains a crystallographically independent Pb^II cation, one L²⁻ ligand, an aqua ligand and half a bpe molecule. Each Pb^II centre is seven‐coordinated by six O atoms of bridging–chelating carboxylate groups from L²⁻ ligands and by one O atom from a coordinated water molecule. The Pb^II cations are bridged by L²⁻ ligands, forming [PbO₂]_n chains along the a axis. These chains are further connected by L²⁻ ligands along the b and c axes to give a three‐dimensional framework with a 4¹²6³ topology. The channel voids are occupied by bpe molecules.