N-atom Acceptors Research Articles

Theoretical Study of the Thermal Decomposition of Urea Derivatives.

An extensive theoretical study of the thermal decomposition of alkyl- and phenylureas, which are widely used in the pesticides, pharmaceuticals, and materials industries, has been carried out using electronic structure calculations and reaction rate theories. Enthalpies of formation and bond dissociation energies (BDE) of 11 urea derivatives have been calculated using different levels of theory (CBS-QB3, CCSD(T)/CBS//M06-2X/6-311++G(3df,2pd), and CBS-QM062X) according to the size of the system. Potential energy surfaces for the unimolecular decomposition pathways of these urea derivatives were also systematically computed for the first time. Several pericyclic reactions can be envisaged, as a function of the size and the nature of the N substituents, and all of these pathways were explored. Our calculations show that these compounds are solely decomposed by four-center pericyclic reactions, yielding substituted isocyanates and amines, and that initial bond fissions are not competitive. Based on the set of urea derivatives studied, a new reaction rate rule for their thermal decomposition was defined and involves the nature of the transferred H atom (primary or secondary/alkyl or benzyl) and the nature of the N-atom acceptor (primary, secondary, or tertiary). This new reaction rate rule allows us to determine the product branching ratios in the thermal decomposition of a given urea derivative and its total rate of decomposition. Applications on urea derivatives used in the chemical industry are presented and illustrate the usefulness of this new rate rule that allows to predict the previously unknown thermal decomposition kinetics of a large number of these compounds.

5-Amino-1-(2',3'-O-iso-propyl-idene-d-ribit-yl)-1H-imidazole-4-carboxamide: a crystal structure with Z' = 4.

The title compound, C12H20N4O5, crystallizes in the monoclinic space group P21, with four crystallographically independent mol-ecules in the asymmetric unit. The four mol-ecules have a very similar conformation that is basically determined by the formation of two intra-molecular hydrogen bonds between the amino NH2 donors and the carbonyl and ring O-atom acceptors, forming, respectively, R(6) and R(7) ring motifs.. In the crystal, inter-molecular hydrogen bonding leads to the formation of R22(10) ring patterns, involving one amide CONH2 donor and an imidazole N-atom acceptor. The cluster of the four independent mol-ecules has approximate non-crystallographic C2 point symmetry. The structural analysis also shows that during the synthesis of the title compound, the reductive cleavage of the d-ribose ring of the inosine precursor proceeds stereoselectively, with retention of configuration.

The coordination complex structures and hydrogen bonding in the three-dimensional alkaline earth metal salts (Mg, Ca, Sr and Ba) of (4-aminophenyl)arsonic acid

(4-Aminophenyl)arsonic acid (p-arsanilic acid) is used as an antihelminth in veterinary applications and was earlier used in the monosodium salt dihydrate form as the antisyphilitic drug atoxyl. Examples of complexes with this acid are rare. The structures of the alkaline earth metal (Mg, Ca, Sr and Ba) complexes with (4-aminophenyl)arsonic acid (p-arsanilic acid) have been determined, viz. hexaaquamagnesium bis[hydrogen (4-aminophenyl)arsonate] tetrahydrate, [Mg(H2O)6](C6H7AsNO3)·4H2O, (I), catena-poly[[[diaquacalcium]-bis[μ2-hydrogen (4-aminophenyl)arsonato-κ2O:O']-[diaquacalcium]-bis[μ2-hydrogen (4-aminophenyl)arsonato-κ2O:O]] dihydrate], {[Ca(C6H7AsNO3)2(H2O)2]·2H2O}n, (II), catena-poly[[triaquastrontium]-bis[μ2-hydrogen (4-aminophenyl)arsonato-κ2O:O']], [Sr(C6H7AsNO3)2(H2O)3]n, (III), and catena-poly[[triaquabarium]-bis[μ2-hydrogen (4-aminophenyl)arsonato-κ2O:O']], [Ba(C6H7AsNO3)2(H2O)3]n, (IV). In the structure of magnesium salt (I), the centrosymmetric octahedral [Mg(H2O)6]2+ cation, the two hydrogen p-arsanilate anions and the four water molecules of solvation form a three-dimensional network structure through inter-species O-H and N-H hydrogen-bonding interactions with water and arsonate O-atom and amine N-atom acceptors. In one-dimensional coordination polymer (II), the distorted octahedral CaO6 coordination polyhedron comprises two trans-related water molecules and four arsonate O-atom donors from bridging hydrogen arsanilate ligands. One bridging extension is four-membered via a single O atom and the other is eight-membered via O:O'-bridging, both across inversion centres, giving a chain coordination polymer extending along the [100] direction. Extensive hydrogen-bonding involving O-H...O, O-H...N and N-H...O interactions gives an overall three-dimensional structure. The structures of the polymeric Sr and Ba complexes (III) and (IV), respectively, are isotypic and are based on irregular MO7 coordination polyhedra about the M2+ centres, which lie on twofold rotation axes along with one of the coordinated water molecules. The coordination centres are linked through inversion-related arsonate O:O'-bridges, giving eight-membered ring motifs and forming coordination polymeric chains extending along the [100] direction. Inter-chain N-H...O and O-H...O hydrogen-bonding interactions extend the structures into three dimensions and the crystal packing includes π-π ring interactions [minimum ring centroid separations = 3.4666 (17) Å for (III) and 3.4855 (8) Å for (IV)].

Crystal structure of 4,5-di-nitro-1H-imidazole.

The title compound, C3H2N4O4, forms crystals with two mol­ecules in the asymmetric unit which are conformationally similar. With the exception of the O atoms of the nitro groups, the mol­ecules are essentially planar. In the crystal, adjacent mol­ecules are associated by N—H⋯N hydrogen bonds involving the imidazole N—H donors and N-atom acceptors of the unsaturated nitro­gen of neighboring rings, forming layers parallel to (010).

Crystal structure of N-[(8E)-12-methyl-14-phenyl-10,13,14,16-tetra-aza-tetra-cyclo-[7.7.0.0(2,7).0(11,15)]hexa-deca-1(16),2,4,6,9,11(15),12-heptaen-8-yl-idene]hydroxyl-amine 1,4-dioxane hemisolvate.

In the title solvate, C19H13N5O·0.5C4H8O2, the main mol­ecule is almost planar (r.m.s. deviation for the non-H atoms = 0.066 Å). The hydroxyl­amine group is disordered over two orientations in a 0.761 (4):0.239 (4) ratio. The complete dioxane solvent mol­ecule is generated by a crystallographic inversion centre. In the crystal, both disorder components of the hydroxyl­amine group form O—H⋯N hydrogen bonds to the same N-atom acceptor, thereby generating [010] chains. The chains encompass [010] channels occupied by the solvent mol­ecules. Aromatic π–π stacking is also observed [shortest centroid–centroid separation = 3.3394 (19) Å].

Crystal structures of 2,6-bis-[(1H-1,2,4-triazol-1-yl)meth-yl]pyridine and 1,1-[pyridine-2,6-diylbis(methyl-ene)]bis-(4-methyl-1H-1,2,4-triazol-4-ium) iodide triiodide.

In the structures of the 2,6-bis-(1,2,4-triazoly-3-yl)methyl-substituted pyridine compound, C11H11N7, (I) and the iodide triiodide salt, C13H17N7 (2+)·I(-)·I3 (-), (II), the dihedral angles between the two triazole rings and the pyridine ring are 66.4 (1) and 74.6 (1)° in (I), and 68.4 (2)° in (II), in which the dication lies across a crystallographic mirror plane. The overall packing structure for (I) is two-dimensional with the layers lying parallel to the (001) plane. In (II), the triiodide anion lies within the mirror plane, occupying the space between the two triazole substituent groups and was found to have minor disorder [occupancy ratio 0.9761 (9):0.0239 (9)]. The overall packing of structure (II) can be described as two-dimensional with the layers stacking parallel to the (001) plane. In the crystal, the predominant inter-molecular inter-actions in (I) and (II) involve the acidic hydrogen atom in the third position of the triazole ring, with either the triazole N-atom acceptor in weak C-H⋯N hydrogen bonds in (I), or with halide counter-ions through C-H⋯I inter-actions, in (II).

Proton-Transfer and Non-transfer Compounds of the Multi-purpose Drug Dapsone [4-(4-Aminophenylsulfonyl)aniline] with 3,5-Dinitrosalicylic Acid and 5-Nitroisophthalic Acid

The structures of the compounds from the reaction of the drug dapsone [4-(4-aminophenylsulfonyl)aniline] with 3,5-dinitrosalicylic acid, the salt hydrate [4-(4-aminophenylsulfonyl)anilinium 2-carboxy-4,6-dinitrophenolate monohydrate] (1) and the 1:1 adduct with 5-nitroisophthalic acid [4-(4-aminophenylsulfonyl)aniline 5-nitrobenzene-1,3-dicarboxylic acid] (2) have been determined. Crystals of 1 are triclinic, space group P-1, with unit cell dimensions a = 8.2043(3), b = 11.4000(6), c = 11.8261(6) Å, α = 110.891(5)°, β = 91.927(3)°, γ = 98.590(4)° and Z = 4. Compound 2 is orthorhombic, space group Pbcn, with unit cell dimensions a = 20.2662(6), b = 12.7161(4), c = 15.9423(5) Å and Z = 8. In 1, intermolecular analinium N–H···O and water O–H···O and O–H···N hydrogen-bonding interactions with sulfone, carboxyl, phenolate and nitro O-atom and aniline N-atom acceptors give a two-dimensional layered structure. With 2, the intermolecular interactions involve both aniline N–H···O and carboxylic acid O–H···O and O–H···N hydrogen bonds to sulfone, carboxyl, nitro and aniline acceptors, giving a three-dimensional network structure. In both structures π–π aromatic ring associations are present. The structures of both an uncommon proton-transfer salt of the drug dapsone with 3,5-dinitrosalicylic acid and a molecular adduct with 5-nitroisophthalic acid are reported, together with their hydrogen-bonding patterns.

3,3′-({4-[(4,5-Dicyano-1H-imidazol-2-yl)diazenyl]phenyl}imino)dipropionic acid

The title compound, C17H15N7O4, is a push–pull non-linear optical chromophore containing a di­alkyl­amino donor group and the di­cyano­imidazolyl acceptor separated by a π-conjugated path. The benzene and imidazole rings are not coplanar, making a dihedral angle of 10.0 (2)°. In the crystal, mol­ecules are linked by an extended set of hydrogen bonds and several motifs are recognized. Pairs of mol­ecules are held together by hydrogen bonding between carb­oxy O—H donor groups and diazenyl N-atom acceptors, forming R 2 2(24) ring patterns across inversion centres. Four-mol­ecule R 4 4(28) ring motifs are formed, again across inversion centres, through hydrogen bonding involving carb­oxy O—H donor groups and diazenyl and imidazole N-atom acceptors. Four-mol­ecule R 4 4(42) patterns are formed among mol­ecules related by translation and involve carb­oxy O—H and imidazole N—H donor groups with carbonyl O-atom and imidazole N-atom acceptors.

2-{[2-(Pyridin-4-yl)-1H-benzimidazol-1-yl]methyl}phenol

In the title compound, C19H15N3O, the benzimidazole ring system makes dihedral angles of 44.36 (7) and 75.67 (7)° with the pyridine and benzene rings, respectively. In the crystal, phenolic O—H⋯N hydrogen bonds to benzimidazole N-atom acceptors give rise to a chain extending along [011].

2,5-Diaminothiophene-3,4-dicarbonitrile

In the title compound, C6H4N4S, the planar mol­ecule lies across a crystallographic mirror plane. In the crystal, the mol­ecules form centrosymmetric dimers through cyclic amino N—H⋯N hydrogen-bonding associations with cyano N-atom acceptors [graph set R 2 2(12)] and these dimers are extended through amine–cyano N—H⋯N associations into a three-dimensional network.

1,4-Bis(4H-1,2,4-triazol-4-yl)benzene dihydrate

The asymmetric unit of the title compound, C10H8N6·2H2O, comprises half the organic species, the mol­ecule being completed by inversion symmetry, and one water mol­ecule. The dihedral angle between the 1,2,4-triazole ring and the central benzene ring is 32.2 (2)°. The water mol­ecules form O—H⋯N hydrogen bonds with N-atom acceptors of the triazole rings. C—H⋯N hydrogen bonds are also observed, giving a three-dimensional framework.

4-{[4-(Hy-droxy-meth-yl)piperidin-1-yl]meth-yl}phenol.

In the title compound, C13H19NO2, the piperidine ring has a chair conformation with the exocyclic N—C bond in an equatorial position. In the crystal, mol­ecules are linked head-to-tail by phenol O—H⋯O hydrogen bonds to hy­droxy­methyl­ene O-atom acceptors, forming chains which extend along [100]. These chains form two-dimensional networks lying parallel to (101) through cyclic hydrogen-bonding associations [graph set R 4 4(30)], involving hy­droxy O—H donors and piperidine N-atom acceptors.

2,6-Bis(4H-1,2,4-triazol-4-yl)pyridine dihydrate

The asymmetric unit of the title compound, C9H7N7·2H2O, comprises three formula units. The dihedral angles between the triazole rings and the respective central pyridine rings are 4.87 (16)/1.39 (17), 6.46 (16)/7.61 (16) and 7.00 (16)/3.77 (17)°. The water mol­ecules form O—H⋯O hydrogen bonds between themselves and O—H⋯N hydrogen bonds with the N-atom acceptors of the triazole rings, producing a three-dimensional framework.

2,6-Bis(4H-1,2,4-triazol-4-yl)pyridine dihydrate

In the asymmetric unit of the title compound, C9H7N7·2H2O, there are two formula units in which the two triazole rings of each of the organic component mol­ecules form dihedral angles of 7.0 (4)/6.9 (4) and 2.7 (4)/3.6 (4)° with the respective central pyridine rings. The four water mol­ecules of solvation form O—H⋯O hydrogen bonds among themselves and O—H⋯N bonds with the N-atom acceptors of the triazine rings, giving a three-dimensional framework structure.

3-Chloropyridin-2-amine

In the title compound, C5H5ClN2, a by-product in the synthesis of ethyl 2-(3-chloro­pyridin-2-yl)-5-oxopyrazolidine-3-carboxyl­ate, the amine groups form inter­molecular hydrogen-bonding associations with pyridine N-atom acceptors, giving centrosymmetric cyclic dimers. Short inter­molecular Cl⋯Cl inter­actions [3.278 (3) Å] also occur.

Sesquicaesium hemisodium tetracyanidoplatinate(II) sesquihydrate

The title compound, Cs1.5Na0.5[Pt(CN)4]·1.5H2O, was isolated from solution as a salt. The tetra­cyanidoplatinate (TCP) anions are stacked in a linear quasi-one-dimensional arrangement along the b axis, with Pt⋯Pt inter­actions of 3.6321 (5) Å. The mixed alkali metal TCP contains three distinct alkali metal positions in the structure that do not show any mixed occupancy: Cs1 (site symmetry 2), Cs2 (general position) and Na1 (site symmetry ). The Na+ ion contains an octa­hedral coordination environment composed of two water mol­ecules and four N-terminal cyanides, which serve to bridge TCP anions. The Cs+ cations contain mono- and bicapped square-prismatic environments, where the square prisms are formed from cyanide N atoms with water mol­ecules capping the faces. The 1.5 water mol­ecules per formula unit are a result of two fully occupied sites, one on a general position and one on a twofold rotation axis. Weak hydrogen-bonding inter­actions are observed between one water mol­ecule and terminal N-atom acceptors from TCP, while the second water mol­ecule is not involved in hydrogen bonding.

μ-1,2-Bis(diphenylphosphino)ethane-κ2P:P′]bis{[1,2-bis(diphenylphosphino)ethane-κ2P,P′]cyanidocopper(I)} methanol disolvate

The title centrosymmetric complex, [Cu2(CN)2(C26H24P2)3]·2CH3OH, consists of two five-membered [Cu(dppe)CN] rings [dppe is 1,2-bis­(diphenyl­phosphino)ethane] bridged by one μ2-dppe ligand, and two methanol solvent mol­ecules. The angles around the central metal atom indicate that each CuI atom is located in the center of a distorted tetra­hedron. The coordination sphere of each CuI atom is formed by three P atoms from two dppe ligands, and one C atom from the cyanide ligand. The crystal structure is stabilized by O—H⋯N hydrogen bonds, which are formed by the O—H donor group from methanol and the N-atom acceptor from a cyanide ligand.

(Acetylacetone 3-hydroxy-2-naphthoylhydrazonato-κ3O,N′,O′)(methoxo-κO)oxidovanadate(V)

The tridentate Schiff base ligand in the title compound, [V(C16H14N2O3)(CH3O)O], has its O, N and O′ atoms spanning three basal positions of the square-based-pyrimidally VV atom. The fourth basal site is occupied by a methoxo ligand, which results from a deprotonated methanol solvent molecule, and the oxido ligand occupies the apical position. The hy­droxy H atom forms an intra­molecular O—H⋯N hydrogen bond with an N-atom acceptor site.

2,2′-o-Phenylenediacetonitrile

In the title compound, NCCH2C6H4CH2CN, the bond lengths and angles are within normal ranges. The benzene ring makes dihedral angles of 4.94 (8) and 77.04 (8)° with the C—C—C—N mean planes. Weak non-conventional C—H⋯N hydrogen bonds are effective in the stabilization of the crystal structure. The weak C—H⋯N contacts form anti­parallel chains running in the a + c direction, and ring systems with two N-atom acceptors and four H-atom donors.

1H-Benzimidazol-2-ylmethyl phenyl ether

There are two mol­ecules in the asymmetric unit of the title compound, C14H10N2O: the dihedral angles between their aromatic ring planes are 47.4 (4) and 46.8 (3)°. In the crystal structure, mol­ecules are linked by N—H⋯N hydrogen bonds from the secondary nitro­gen N—H donor to the tertiary N-atom acceptor of a symmetry-related neighbour, resulting in hydrogen-bonded chains. The two independent chains both propagate in [100].