Crystal structures of 2,4,6-tri-iodo-benzo-nitrile and 2,4,6-tri-iodo-phenyl isocyanide.

The title crystals, C7H2I3N, are isomorphous. Both mol-ecules lie across two crystallographic mirror planes and a twofold axis. The principal supra-molecular inter-action is centric R22(10) CN/NC⋯I short contacts involving both ortho I atoms, with two contacts bis-ecting each cyano and iso-cyano group. These form ribbons along [010] and give rise to a planar sheet structure parallel to (100). All pairs of adjacent sheets have centric stacking, a mode not previously reported for sheets of this type. This study completes the series of homo-2,4,6-trihalobenzo-nitriles, in which I atoms give the strongest CN⋯X and NC⋯X inter-actions (X = F, Cl, Br, I).

Two new polytypes of 2,4,6-tri-bromo-benzo-nitrile.

Three polymorphs of 2,4,6-tri-bromo-benzo-nitrile (RCN), C7H2Br3N, two of which are novel and one of which is a redetermination of the original structure first determined by Carter & Britton [(1972). Acta Cryst. B28, 945-950] are found to be polytypic. Each has a layer structure which differs only in the stacking of the layers. Each layer is composed of mol-ecules associated through C N⋯Br contacts which form R (2) 2(10) rings. Two such rings are associated with each N atom; one with each ortho-Br atom. No new polytypes of 1,3,5-tri-bromo-2-iso-cyano-benzene (RNC) were found but a re-determination of the original structure by Carter et al. [(1977). Cryst. Struct. Commun. 6, 543-548] is presented. RNC was found to be isostructural with one of the novel polytypes of RCN. Unit cells were determined for 23 RCN samples and 11 RNC samples. Polytypes could not be distinguished based on crystal habits. In all four structures, each mol-ecule of the asymmetric unit lies across a mirror plane.

Unexpectedly Stable (Chlorocarbonyl)(N-ethoxycarbonylcarbamoyl)disulfane, and Related Compounds That Model the Zumach-Weiss-Kühle (ZWK) Reaction for Synthesis of 1,2,4-Dithiazolidine-3,5-diones.

The Zumach-Weiss-Kühle (ZWK) reaction provides 1,2,4-dithiazolidine-3,5-diones [dithiasuccinoyl (Dts)-amines] by the rapid reaction of O-ethyl thiocarbamates plus (chlorocarbonyl)sulfenyl chloride, with ethyl chloride and hydrogen chloride being formed as coproducts, and carbamoyl chlorides or isocyanates generated as yield-diminishing byproducts. However, when the ZWK reaction is applied with (N-ethoxythiocarbonyl)urethane as the starting material, heterocyclization to the putative "Dts-urethane" does not occur. Instead, the reaction directly provides (chlorocarbonyl)(N-ethoxycarbonylcarbamoyl)disulfane, a reasonably stable crystalline compound; modified conditions stop at the (chlorocarbonyl)[1-ethoxy-(N-ethoxycarbonyl)formimidoyl]disulfane intermediate. The title (chlorocarbonyl)(carbamoyl)disulfane cannot be converted to the elusive Dts derivative, but rather gives (N-ethoxycarbonyl)carbamoyl chloride upon thermolysis, or (N-ethoxycarbonyl)isocyanate upon treatment with tertiary amines. Additional transformations of these compounds have been discovered, providing entries to both known and novel species. X-ray crystallographic structures are reported for the title (chlorocarbonyl)(carbamoyl)disulfane; for (methoxycarbonyl)(N-ethoxycarbonylcarbamoyl)disulfane, which is the corresponding adduct after quenching in methanol; for [1-ethoxy-(N-ethoxycarbonyl)formimidoyl](N'-methyl-N'-phenylcarbamoyl)disulfane, which is obtained by trapping the title intermediate with N-methylaniline; and for (N-ethoxycarbonylcarbamoyl)(N'-methyl-N'-phenylcarbamoyl)disulfane, which is a short-lived intermediate in the reaction of the title (chlorocarbonyl)(carbamoyl)disulfane with excess N-methylaniline. The new chemistry and structural information reported herein is expected to contribute to accurate modeling of the ZWK reaction trajectory.

Four polymorphs (polytypes) of 5,6-dimethylbenzofurazan 1-oxide.

5,6-Dimethylbenzofurazan 1-oxide (Me2BF), C(8)H(8)N(2)O(2), occurs in four polymorphic forms that are polytypes of each other. Each polymorph of Me2BF contains molecules disordered about pseudo-twofold axes and arranged head-to-tail in ribbons, with the ribbons forming approximately planar layers held together by weak C-H···N and C-H···O interactions. Adjacent layers interact in different ways in the different polymorphs. In addition to twinning in the individual polymorphs, four examples of allotwining, that is, oriented overgrowths between different polymorphs, were found.

Planar packing of tetrachlorodicyanobenzenes. II.

Equimolar mixtures of ortho- and meta-, or ortho- and para-, or meta- and para-tetrachlorodicyanobenzene, C(6)Cl(4)(CN)(2), form structures with disordered layers containing both kinds of molecules in rhombohedral or pseudo-rhombohedral cells. These structures are similar to the structure of the rhombohedral form of the meta isomer. The guiding force appears to be an intermolecular synthon, in which a nitrile group in one molecule interacts with Cl atoms in two adjacent molecules with N...Cl distances of approximately 3.1 A.

2,4,6-trifluorobenzonitrile.

The title compound, C(7)H(2)F(3)N, contains three crystallographically independent molecules in the crystal structure; two of these molecules have symmetry m and the third has symmetry mm. Each independent molecule forms a planar or approximately planar layer with its own kind. There are three different types of interlayer contacts, two of which are similar to each other, while the third is distinctly different. The packing within the layers is similar to that found in 2,5- and 3,6-difluorobenzonitrile, with weak C-H...N interactions holding the molecules in the layers. The remarkable feature of this structure is the presence of more than one type of interlayer interaction.

5-Iodobenzofurazan 1-oxide: polymorphs, pseudosymmetry and disorder.

5-Iodobenzofurazan 1-oxide (systematic name: 5-iodobenzo-1,2,5-oxadiazole 1-oxide), C(6)H(3)IN(2)O(2), occurs in two polymorphic forms, both monoclinic in P2(1)/c with Z' = 2. The intermolecular interactions in the two polymorphs are quite different. In polymorph (I), there are strong intermolecular I...O interactions, with I...O distances of 3.114 (8) and 3.045 (8) A. In polymorph (II), there are strong intermolecular I...N interactions, with I...N distances of 3.163 (4) and 3.175 (5) A. In (I), there is about 15% disorder in one molecule and about 5% in the other. In both polymorphs, there are pseudosymmetric relationships between the crystallographically independent molecules.

3,4,6-Trichloro-5-cyano-2-hydroxybenzamide.

The title compound, C(8)H(3)Cl(3)N(2)O(2), forms crystals in which hydrogen-bonding and Cl...N interactions appear to be equally important to the structure. The molecules form ribbons held together alternately by cyclic (CONH)(2) and cyclic (ClCCC[triple-bond]N)(2) interactions. The ribbons assemble into layers through Cl...Cl interactions. The layers are held together by NH...N[triple-bond]C hydrogen bonds, as well as by pi-pi interactions.

4-(4-Chlorobenzylidenehydrazonomethyl)benzonitrile and the bromo and iodo analogs.

4-Cyano-4'-chlorobenzalazine [systematic name: 4-(4-chlorobenzylidenehydrazonomethyl)benzonitrile], C(15)H(10)ClN(3), occurs in two polymorphs. Polymorph A is isostructural with the corresponding dichloro compound. Polymorph B is isostructural with the bromo and iodo analogs, viz. C(15)H(10)BrN(3) and C(15)H(10)IN(3), respectively. The latter three structures all have approximately linear C-N...X-C intermolecular contacts in which the N...X contact distances are longer than those in the corresponding benzylideneanilines.

o-Chloro- and o-bromobenzonitrile: pseudosymmetry and pseudo-isostructural packing.

The structures of o-chlorobenzonitrile, C7H4ClN, (I), and o-bromobenzonitrile, C7H4BrN, (II), have similar packing arrangements, even though Z' = 4 in (I) and Z' = 1 in (II). Both structures involve X...N interactions, as well as weak C-H...X and C-H...N hydrogen bonds. The four crystallographically independent molecules in (I) are related by pseudosymmetry.

2-Formylbenzonitrile.

The title compound, C8H5NO, has an intramolecular O...CN contact involving an O...C distance of 2.797 (2) angstroms and a C-C-N bond angle of 174.5 (2) degrees, both indicative of a weak nucleophilic attack of the aldehyde O atom on the electrophilic C atom in the nitrile group. Calculations at the B3LYP density functional level using the 6-31G* basis set support this interpretation; natural bond-order analysis indicates an n(O1) --> pi(CN)* delocalization energy of 6.3 kJ mol(-1). Similar results were obtained from density functional calculations on three related molecules. The 2-formylbenzonitrile molecules pack in sheets as a consequence of C-H...N and C-H...O hydrogen bonds.

Dimethyl- and diethyldithiocyanatotin(IV).

The structures of dimethyldithiocyanatotin(IV), [Sn(CH3)2(NCS)2], and diethyldithiocyanatotin(IV), [Sn(C2H5)2(NCS)2], have been determined. The dimethyl derivative has 2mm crystallographic symmetry and the diethyl derivative has twofold crystallographic symmetry. The experimental differences in the distances and angles around the Sn atom between the two structures agree reasonably well with the differences expected from the reaction path mapped previously [Britton & Dunitz (1981). J. Am. Chem. Soc. 103, 2971-2979].

3,5-Dihalo-4-hydroxybenzonitriles: isostructures, polymorphs and solvates.

3,5-Dichloro-4-hydroxybenzonitrile and its solvates with benzene and xylene assemble in chain-like arrangements held together by OH...NC interactions. Two polymorphs each of the corresponding dibromo and diiodo compounds form similar chains which are then bound together by X...X interactions to form approximately planar sheets. These sheets are essentially identical in all four of the bromo and iodo compounds and have approximate p2gg two-dimensional symmetry. These four compounds form an extreme example of two-dimensional isostructuality. The polymorphs differ in the stacking arrangements. One of the Br polymorphs is isostructural with one of the I polymorphs.

1:1 complexes of 2,3,5,6-tetrachlorobenzene-1,4-dicarbonitrile with pyrene and phenanthrene: pseudo-isomorphs.

2,3,5,6-Tetrachlorobenzene-1,4-dicarbonitrile forms alternate pi-stacked 1:1 complexes with pyrene, C(8)Cl(4)N(2).C(16)H(10), and phenanthrene, C(8)Cl(4)N(2).C(14)H(10). These complexes are pseudo-isomorphs. Phenanthrene, disordered about a centre of symmetry, takes the position of the pyrene, which sits exactly on this centre of inversion. The tetrachlorobenzenedicarbonitrile molecules in each complex also sit on centres of inversion and are in similar positions within the unit cells in the two structures, except that the orientation of the nitrile groups differs between the two.

4'-Hydroxybiphenyl-4-carbonitrile.

The title compound, C13H9NO, crystallizes with four molecules in the asymmetric unit. Each of the four crystallographically independent molecules forms a chain parallel to the a axis with symmetry-equivalent molecules. These chains are held together by similar O-H...NC hydrogen bonds, with approximately linear O-H...N angles and significantly bent H...N-C angles. The four different molecules are related by strong elements of pseudosymmetry. To better describe the pseudosymmetry, the structure has been reported in the non-standard space group C-1.

p-Decylphenyl isocyanide and p-decylbenzonitrile: isomorphous isonitrile/nitrile isomers.

p-Decylphenyl isocyanide, p-C(10)H(21)-C(6)H(4)-NC or C(17)H(25)N, and p-decylbenzonitrile, p-C(10)H(21)-C(6)H(4)-CN or C(17)H(25)N, are isomorphous. The molecules lie in mirror planes, with the C(6) rings perpendicular to the mirror. The packing of both molecules includes an aliphatic region, with close to ideal packing of the C(10)H(21) chains, and an aromatic region, with phenyl ring-CN interactions. In addition, the CN ends of the molecules are also involved in a CN.NC dipolar interaction.

Diiododurene: four centrosymmetric molecules in general positions.

Diiododurene (1,4-diodo-2,3,5,6-tetramethylbenzene), C(10)H(12)I(2), packs with four molecules in the asymmetric unit. All four of these moleules violate Kitaigorodsky's suggestion that molecules with centers of symmetry will lie on crystallographic centers of symmetry. There is 5.6% disorder at one of the sites. Most of the I atoms are in contact with other I atoms, but only six of the I.I contacts are shorter than 4.2 A. Of these six contacts, one set of three contacts forms a triangular set in which all of the I.I distances are less than 3.9 A.

Five (1H-pyrrol-2-yl)pyridines.

The title (1H-pyrrol-2-yl)pyridines, C(9)H(8)N(2), substituted at the ortho, meta, and para positions of the pyridine ring all have hydrogen-bonded arrangements with geometrically similar, nearly linear, N(pyrrole)-H...N(pyridine) hydrogen bonds of average length. The graph sets for the ortho, meta, and three para polymorphs are R(2)(2)(10), C(6), C(7), C(7), and R(4)(4)(28), respectively.