N—H⋯N and C—H⋯π inter­actions in 4‐amino‐3‐methyl‐5‐(p‐tol­yl)‐4H‐1,2,4‐triazole and 4‐amino‐3‐methyl‐5‐phenyl‐4H‐1,2,4‐triazole

The title compounds, C₁₀H₁₂N₄, (I), and C₉H₁₀N₄, (II), have been synthesized and characterized both spectroscopically and structurally. The dihedral angles between the triazole and benzene ring planes are 26.59 (9) and 42.34 (2)°, respectively. In (I), mol­ecules are linked principally by N—H⋯N hydrogen bonds involving the amino NH₂ group and a triazole N atom, forming R₄⁴(20) and R₂⁴(10) rings which link to give a three‐dimensional network of mol­ecules. The hydrogen bonding is supported by two different C—H⋯π inter­actions from the tolyl ring to either a triazole ring or a tolyl ring in neighboring mol­ecules. In (II), inter­molecular hydrogen bonds and C—H⋯π inter­actions produce R₃⁴(15) and R₄⁴(21) rings.     

4‐(Pyrrol‐1‐yl)‐1,2,4‐triazole

The asymmetric unit of the title compound, C₆H₆N₄, comprises one and a half molecules with a C₂ axis through the second molecule. Each molecule consists of two planar five‐membered rings connected by a triazole–pyrrole N—N bond with the triazole ring close to being at right angles to the pyrrole ring. The molecules are linked by C—H...N hydrogen bonds and weaker offset face‐to‐face π–π interactions.     

5‐Amino‐4‐(4‐diethylaminophenyl)‐2‐phenyl‐7‐(pyrrolidin‐1‐yl)‐1,6‐naph­thyridine‐8‐carbonitrile

In the title compound, C₂₉H₃₀N₆, the naphthyridine ring is almost planar with a dihedral angle of 5.4 (1)° between the pyridyl rings. The dihedral angles between the naphthyridine system and the diethyl­amino­phenyl, phenyl and pyrrolidine rings are 53.1 (1), 19.8 (1) and 20.9 (1)°, respectively. The pyrrolidine ring adopts a half‐chair conformation. The mol­ecule is stabilized by weak C—H?N interactions.     

2‐Amino‐4‐(4‐pyridyl)­pyrimidine and the 1:1 adduct with 4‐amino­benzoic acid

The structure of the title compound, C₉H₈N₄, comprises non‐planar mol­ecules that associate via pyrimidine N—H?N dimer R(8) hydrogen‐bonding associations [N?N 3.1870 (17) Å] and form linear hydrogen‐bonded chains via a pyrimidine N—H?N(pyridyl) interaction [N?N 3.0295 (19) Å]. The dihedral angle between the two rings is 24.57 (5)°. The structure of the 1:1 adduct with 4‐amino­benzoic acid, C₉H₈N₄·C₇H₇NO₂, exhibits a hydrogen‐bond­ing network involving COOH?N(pyridyl) [O?N 2.6406 (17) Å], pyrimidine N—H?N [N?N 3.0737 (19) and 3.1755 (18) Å] and acid N—H?O interactions [N?O 3.0609 (17) and 2.981 (2) Å]. The dihedral angle between the two linked rings of the base is 38.49 (6)° and the carboxyl­ic acid group binds to the stronger base group in contrast to the (less basic) complementary hydrogen‐bonding site.     

2‐[4‐Phenyl‐5‐(2‐pyridyl)‐4H‐1,2,4‐triazol‐3‐yl]nicotinic acid: a case of solvent‐dependent polymorphism

The title compound, C₁₉H₁₃N₅O₂, crystallizes in two monoclinic forms depending on the solvent used. From methanol or acetone, a yellow form [(Ia), m.p. 533 K] in the space group P2₁ is obtained, while with ethanol as the solvent, an orange form [(Ib), m.p. 541 K] in the space group Cc results. The conformers observed in the two polymorphs differ primarily in the relative orientation of pyridine/phenyl and triazole rings. Molecules of both polymorphs form chains through carboxyl O—H...N hydrogen bonding; however, in each crystal structure, a different group acts as acceptor, viz. a triazole and a pyridyl N atom for (Ia) and (Ib), respectively. This is the first case of polymorphism observed for crystals of a 3,4,5‐trisubstituted 1,2,4‐triazole derivative.     

trans‐4‐[4‐(Dimethylamino)phenyl­iminomethyl]‐N‐phenylpyridinium hexafluorophosphate

The crystal structure of the dipolar chromophoric title compound, C₂₀H₂₀N₃⁺·PF₆^?, is described. The phenyl­ene and pyridyl rings are almost coplanar [dihedral angle 7.5 (2)°], but the phenyl substituent forms a dihedral angle of 56.6 (1)° with the pyridyl ring. The compound crystallizes in the non‐centrosymmetric space group Cc and is a likely candidate for the display of quadratic non‐linear optical effects.     

N‐Cyclo­hexyl‐2‐[5‐(4‐pyridyl)‐4‐(p‐tolyl)‐4H‐1,2,4‐triazol‐3‐yl­sulfanyl]­acetamide dihydrate

In the title compound, C₂₂H₂₅N₅OS·2H₂O, the mol­ecules are stacked in columns running along the b axis. In this arrangemant, the mol­ecules are linked to each other by a combination of one two‐centre N—H⋯O hydrogen bond and four two‐centre O—H⋯O hydrogen bonds containing two types of ring motif, viz.R₄⁴(10) and R₃³(11). In the crystal structure, centrosymmetric π–π inter­actions between the triazole rings, with a distance of 3.691 (2) Å between the ring centroids, also affect the packing of the mol­ecules.     

The infinite double‐stranded chain polymer catena‐poly­[[bis­(dicyan­amido)­zinc(II)]‐di‐μ‐1,2‐bis(1,2,4‐triazol‐1‐yl)­ethane‐κ4N4:N4′]

The coordination geometry of the Zn^II atom in the title complex, [Zn(C₂N₃)₂(C₆H₈N₆)₂]_n or [Zn(dca)₂(bte)₂]_n, where bte is μ‐1,2‐bis(1,2,4‐triazol‐1‐yl)­ethane and dca is dicyan­amide, is distorted compressed octahedral, in which the Zn^II atom lies on an inversion center and coordinates four N atoms from the triazole rings of four symmetry‐related bte ligands and two N atoms from two symmetry‐related monodentate dca ligands. The structure is polymeric, with 18‐membered spiro‐fused rings extending in the b direction and each 18‐membered ring involving two inversion‐related bte mol­ecules.     

Racemic isopropyl 1,4‐dihydro‐2,6‐dimethyl‐4‐(6‐methyl‐2‐pyridyl)‐3‐nitropyridine‐5‐carboxylate hemi­benzene solvate

This analysis establishes the rotameric orientation of the pyridyl‐ring N atom of the title compound, C₁₇H₂₁N₃O₄·0.5C₆H₆, as antiperiplanar (ap) to the 1,4‐dihydropyridine H‐4, the absence of an intramolecular hydrogen bond between the 1,4‐dihydropyridine NH and the pyridyl‐N atom, and the unusual planarity of the 1,4‐dihydropyridine ring.     

4,4′‐(Azinodimethylene)dipyridinium bis(tetrafluoroborate) and 4‐[(4‐pyridylmethylene)hydrazonomethyl]pyridinium perchlorate: two different hydrogen‐bonding motifs

In the crystal structures of the title compounds, C₁₂H₁₂N₄²⁺·2BF₄⁻, (I), and C₁₂H₁₁N₄⁺·ClO₄⁻, (II), respectively, infinite two‐ and one‐dimensional architectures are built up via N—H...F [in (I)] and conventional N—H...N [in (II)] hydrogen bonding. The N—N single bond in (I) lies on a crystallographic centre of symmetry; as a result, the two pyridinium rings are parallel. In (II), the pyridinium and pyridyl ring planes are inclined with a dihedral angle of 14.45 (3)°.     

[5‐Benzyl‐3‐phenyl‐2‐(2‐pyridyl‐κN)thiazolidin‐4‐one‐κS]dichloropalladium(II)

The palladium(II) centre in the title compound, [PdCl₂(C₂₁H₁₈N₂OS)], is coordinated to the pyridyl N atom and to the thia­zolidinone S atom of the 5‐benzyl‐3‐phenyl‐2‐(2‐pyridyl)­thia­zolidin‐4‐one ligand, resulting in a five‐membered chelate ring. Two cis‐chloro ligands complete the square‐planar coordination environment of the metal. Although the geometry at the Pd centre is essentially planar, the N—Pd—S bite angle of 85.20 (8)° causes deviations in the cis angles from the ideal value of 90°. Opposite enantiomers form one‐dimensional chains in the cell via a short S?O intermolecular interaction.     

3‐(2‐Furyl)‐6‐(4‐methyl­phenyl)‐7H‐1,2,4‐triazolo­[3,4‐b][1,3,4]thia­diazine and its 6‐phenyl analogue

In the title compounds, C₁₅H₁₂N₄OS, (I), and C₁₄H₁₀N₄OS, (II), the thia­diazine ring adopts a skew‐boat conformation, while the triazole and furyl rings are essentially planar. The phenyl group is twisted by 33.5 (2) and 47.9 (1)° out of the triazole‐ring plane in (I) and (II), respectively.     

catena‐Poly[[diaquadiisothiocyanatoiron(II)]‐μ‐4,4′‐bi‐1,2,4‐triazole]: a one‐dimensional coordination polymer

In the title complex, [Fe(NCS)₂(C₄H₂N₆)₂(H₂O)₂]_n, the Fe^II atom is on an inversion centre and the 4,4′‐bi‐1,2,4‐triazole (btr) group is bisected by a twofold axis through the central N—N bond. The coordination geometry of the Fe^II atom is elongated distorted FeN₄O₂ octahedral, where the cation is coordinated by two N atoms from the triazole rings of two btr groups, two N atoms from NCS⁻ ligands and two water molecules. Btr is a bidentate ligand, coordinating one Fe^II atom through a peripheral N atom of each triazole ring, leading to a one‐dimensional polymeric (chain) structure extending along [101]. The chains are further connected through a network of O—H...N and C—H...S hydrogen bonds.     

catena‐Poly[[silver(I)‐μ‐[(E)‐1,2‐bis(2‐pyridyl)ethylene‐N:N′]] nitrate]

In the title complex, {[Ag(C₁₂H₁₀N₂)]NO₃}_n, the Ag atom, which is in a linear AgN₂ geometry, is surrounded by two trans‐related N atoms of two bpe ligands [Ag—N = 2.173 (3) and 2.176 (3) Å; bpe is trans‐1,2‐bis(2‐pyridyl)­ethyl­ene]. The bpe ligands bridge neighbouring Ag atoms to form zigzag polymeric chains in the lattice. These adjacent one‐dimensional zigzag chains are extended into a three‐dimensional supramolecular array by strong interchain π?π interactions between the pyridyl rings of adjacent chains.     

catena‐Poly[[diisothio­cyanato­cad­mium(II)]‐bis­[μ‐1,3‐bis­(1,2,4‐triazol‐1‐ylmeth­yl)benzene‐κ2N4:N4′]]: a double‐chain coordination polymer

The coordination geometry of the Cd^II atom in the title complex, [Cd(NCS)₂(C₁₂H₁₂N₆)₂]_n or [Cd(NCS)₂(mbtz)₂]_n, where mbtz is 1,3‐bis­(1,2,4‐triazol‐1‐ylmeth­yl)benzene, is a distorted compressed octa­hedron in which the Cd^II atom lies on an inversion centre, coordinated by four N atoms from the triazole rings of four mbtz ligands and two N atoms from two monodentate NCS⁻ ligands. The structure is polymeric, with 24‐membered spiro‐fused rings extending along [100] and with the 24‐membered ring containing two inversion‐related mbtz mol­ecules.     

Tetrakis­[1‐(3‐chloro­propyl)‐1,2,4‐tri­azole‐κN4]­bis­(tetrafluoroborato‐κF)copper(II)

In the title complex, [Cu(BF₄)₂(1tpc)₄] [1tpc is 1‐(3‐chloro­propyl)‐1,2,4‐triazole, C₅H₈ClN₃], the copper(II) centres reside in a tetragonally distorted octahedral coordination environment. Four 1tpc ligands are coordinated to the metal atom via the N4 atom of the triazole rings in a square‐planar arrangement, with Cu—N bond lengths in the range 2.002 (2)–2.019 (2) Å. Two tetra­fluoro­borate anions, in the axial positions above and below the square plane, are weakly coordinated to the copper(II) centre, with Cu—F distances of 2.4009 (18) and 2.5096 (18) Å.     

5‐Nitro‐2,3‐bis(2‐pyridyl)­quinoxaline

In the crystal structure of the title compound, C₁₈H₁₁N₅O₂, two crystallographically independent mol­ecules having the same composition and cis–cis conformation (arrangement of the pyridyl rings) are observed. A C—H⃛N hydrogen bond links the centrosymmetrically related mol­ecules into a discrete pair [C⃛N = 3.462 (4) Å], and the structure is stabilized further by π–π‐stacking interactions between aromatic rings from two adjacent dimers.     

4‐Chloro­aceto­phenone [1‐(4‐methoxyphenyl)­ethyl­idene]­hydra­zone

The crystal structure of the title mixed azine, C₁₇H₁₇ClN₂O, contains four independent mol­ecules, A–D, and mol­ecule B is disordered. All four mol­ecules have an N—N gauche conformation, with C—N—N—C torsion angles of 136.5 (4), 137.0 (4), ?134.7 (4) and ?134.7 (4)°, respectively. The phenyl rings are also somewhat twisted with respect to the plane defined by C_ipso and the imine bond. On average, the combined effect of these twists results in an angle of 64.7° between the best planes of the two phenyl rings. Arene–arene double T‐contacts are the dominant intermolecular inter­action. The methoxy‐substituted phenyl ring of one azine mol­ecule interacts to form a T‐contact with the methoxy‐substituted phenyl ring of an adjacent mol­ecule and, similarly, two chloro‐substituted phenyl rings of neighboring mol­ecules interact to form another T‐contact. The only exception is for mol­ecule B, for which the disorder leads to the formation of T‐­contacts between methoxy‐ and chloro‐substituted phenyl rings. The prevailing structural motif of T‐contact formation between like‐substituted arene rings results in a highly dipole‐parallel‐aligned crystal structure.     

Alkylations of N4‐(4‐Pyridyl)‐3,5‐di(2‐pyridyl)‐1,2,4‐triazole: First Observation of Room‐Temperature Rearrangement of an N4‐Substituted Triazole to the N1 Analogue

Attempts to use alkylation to introduce a positive charge at the nitrogen atom of the 4‐pyridyl ring in the bis(bidentate) triazole ligand N⁴‐(4‐pyridyl)‐3,5‐di(2‐pyridyl)‐1,2,4‐triazole ( pydpt ) were made to ascertain what effect a strongly electron‐withdrawing group would have on the magnetic properties of any subsequent iron(II) complexes. Alkylation of pydpt under relatively mild conditions led in some cases to unexpected rearrangement products. Specifically, when benzyl bromide is used as the alkylating agent, and the reaction is carried out in refluxing acetonitrile, the N⁴ substituent moves to the N¹ position. However, when the same reaction is performed in dichloromethane at room temperature, the rearrangement does not occur and the desired product containing an alkylated N⁴ substituent is obtained. Heating a pure sample of N⁴‐Bzpydpt?Br to reflux in MeCN resulted in clean conversion to N1Bzpydpt.Br . This is consistent with N4‐Bzpydpt.Br being the kinetic product whereas N1Bzpydpt.Br is the thermodynamic product. When methyl iodide is used as the alkylating agent, the N⁴ to N¹ rearrangement occurs even at room temperature, and at reflux pydpt is doubly alkylated. The observation of the lowest reported temperatures for an N⁴ to N¹ rearrangement is due to this particular rearrangement involving nucleophilic aromatic substitution: a possible mechanism for this transformation is suggested.     

(Z)‐7‐Chloro‐3‐[(3‐chloro­phenyl)­methyl­idene]‐4‐p‐tosyl‐3,4‐di­hydro‐2H‐1,4‐benzoxazine

In the title compound, C₂₂H₁₇Cl₂NO₃S, the mol­ecule is a substituted 3,4‐di­hydro‐2H‐1,4‐benzoxazine compound which has three phenyl rings which are essentially planar. The 3,4‐di­hydro‐2H‐oxazine part of the mol­ecule is fused to the benzo ring and has a half‐boat conformation; the dihedral angle between the planar part of the oxazine ring and the benzo ring is 10.2 (2)°. The (3‐chloro­phenyl)­methyl­idene substituent has a Z configuration in relation to the ring N atom of the oxazine moiety. Interestingly, the p‐toluenesulfonyl (p‐tosyl) substituent on the ring N atom protrudes away from the 3‐­chloro­phenyl substituent thus avoiding any steric interaction.