3-Acetyl-1-(3-methyl­phen­yl)-5-phenyl-1H-pyrazole-4-carbonitrile

In the title compound, C₁₉H₁₅N₃O, the central pyrazole ring makes dihedral angles of 35.52 (12) and 62.21 (11)° with the attached phenyl and methyl-substituted phenyl rings, respectively. The corresponding angle between the phenyl and methyl-substituted phenyl rings is 62.90 (11)°. In the crystal, mol­ecules are connected by weak C—H...O hydrogen bonds, forming supra­molecular chains propagating along the a-axis direction.

5,6-Dimethyl-4-(thio­phen-2-yl)-1H-pyrazolo­[3,4-b]pyridin-3-amine

In the title mol­ecule, C₁₂H₁₂N₄S, the thio­phene ring is disordered over two orientations with a refined site-occupancy ratio of 0.777 (4):0.223 (4). The pyrazolo­pyridine ring system is essentially planar with an r.m.s. deviation of 0.0069 (3) Å and makes dihedral angles of 82.8 (2) and 72.6 (5)°, respectively, with the major and minor components of the thio­phene ring. In the crystal, mol­ecules are linked into a chain along the a axis by a pair of N—H...N(pyrazole) hydrogen bonds and a pair of N—H...N(pyridine) hydrogen bonds, both having a centrosymmetric R₂²(8) graph-set motif. A C—H...π inter­action is also present.

3-(1H-Imidazol-1-yl)-1-phenyl­propan-1-ol

In the title compound, C₁₂H₁₄N₂O, the imidazole ring forms a dihedral angle of 66.73 (5)° with the phenyl ring. In the crystal, mol­ecules are linked via O—H...N and C—H...O hydrogen bonds into sheets lying parallel to (100). The crystal structure is further consolidated by C—H...π inter­actions.

(1Z,2E)-N′-{2-Chloro-1-methyl-2-[2-(4-methyl­phen­yl)hydrazin-1-yl­idene]ethyl­idene}-4-meth­oxy­benzohydrazide

The asymmetric unit of the title compound, C₁₈H₁₉ClN₄O₂, contains two mol­ecules, in which the dihedral angles between the benzene rings are 43.60 (12) and 58.65 (13)°. The hydrazine N atoms are twisted slightly out of the planes of the tolyl and meth­oxy­benzene rings: the C—C—N—N and N—N—C—C torsion angles are 171.1 (2) and −174.4 (2)°, respectively, for one mol­ecule and −177.4 (2) and −170.6 (2)°, respectively, for the other. In the crystal, mol­ecules are linked by N—H...O and C—H...O hydrogen bonds into chains propagating along the b-axis direction.

(E)-N′-(4-Isopropyl­benzyl­idene)isonicotinohydrazide monohydrate

In the title compound, C₁₆H₁₇N₃O·H₂O, the isonicotinohydrazide mol­ecule adopts an E conformation about the central C=N double bond. The dihedral angle between the pyridine and the benzene rings is 54.56 (15)°. In the crystal, mol­ecules are connected via N—H...O, O—H...N and O—H...O hydrogen bonds, forming a three-dimensional network.

1-(4-Methyl­phen­yl)-2-(phenyl­sulfon­yl)ethanone

In the title compound, C₁₅H₁₄O₃S, the benzene and phenyl rings make a dihedral angle of 33.56 (16)°. In the crystal, mol­ecules are linked by C—H...O hydrogen bonds into a layer parallel to the ab plane.

3-Chloro-4-methyl­quinolin-2(1H)-one

The title compound, C₁₀H₈ClNO, is almost planar (r.m.s. deviation for the 13 non-H atoms = 0.023 Å). In the crystal, inversion dimers linked by pairs of N—H...O hydrogen bonds generate R₂²(8) rings. Weak aromatic π–π stacking inter­actions [centroid–centroid distance = 3.7622 (12) Å] also occur.

3-Acetyl-1,5-diphenyl-1H-pyrazole-4-carbonitrile

The title compound, C₁₈H₁₃N₃O, has a butterfly-like structure, in which the pyrazole ring forms dihedral angles of 59.31 (8) and 57.24 (8)° with the two phenyl rings. The dihedral angle between the two phenyl rings is 64.03 (8)°. The pyrazole ring and the C—C=O plane of the acetyl group are twisted slightly, making a dihedral angle of 7.95 (18)°. In the crystal, mol­ecules are linked through weak C—H...N and C—H...O inter­actions into a helical chain along the a-axis direction.

(E)-2-(2,3-Dimethyl­anilino)-N′-[2-methyl-5-(prop-1-en-2-yl)cyclo­hex-2-enyl­idene]benzohydrazide

The asymmetric unit of the title compound, C₂₅H₂₉N₃O, comprises two crystallographically independent mol­ecules. The dihedral angles between the benzene rings in the two mol­ecules are 59.7 (2) and 61.27 (18)°. The cyclo­hexene rings adopt sofa and half-chair conformations. In the crystal, mol­ecules are connected via N—H...O and weak C—H...O hydrogen bonds, forming chains along the a axis. In each mol­ecule, there is an intra­molecular N—H...O hydrogen bond.

(Z)-3-p-Tolyl-2-(p-tolyl­imino)-1,3-thia­zolidin-4-one

In the title compound, C₁₇H₁₆N₂OS, the central thia­zolidin-4-one ring forms dihedral angles of 66.49 (9) and 79.45 (6)° with the two methyl-substituted benzene rings. In the crystal, mol­ecules are stacked in columns along the b axis through C—H...π inter­actions. The H atoms of one of the methyl groups are disordered over two orientations with equal site occupancies.

N′-[(1E,2E)-3,7-Dimethyl­octa-2,6-dien-1-yl­idene]pyridine-4-carbohydrazide

In the title compound, C₁₆H₂₁N₃O, the mol­ecule adopts an E conformation about the central C=N double bond. The 2-methyl­pent-2-ene group is disordered over two sets of sites, with a refined occupancy ratio of 0.785 (8):0.215 (8). The dihedral angle between the essentially planar [the r.m.s. value for the major component is 0.021 (7) and its maximum deviation is 0.025 (4) Å; the r.m.s. value for the minor component is 0.03 (4) and its maximum deviation is 0.05 (3) Å] major and minor components of the 2-methyl­but-2-ene group is 35.9 (13)°. In the crystal, C—H...O and N—H...O hydrogen bonds link the molecules, with the same O atom acting as the acceptor. This results in C¹₁(4) and C¹₁(5) [001] chains.

3-Acetyl-5-phenyl-1-p-tolyl-1H-pyrazole-4-carbonitrile

In the title pyrazole derivative, C₁₉H₁₅N₃O, the central pyrazole ring makes dihedral angles of 42.71 (9) and 61.34 (9)°, respectively, with the phenyl and p-tolyl rings. The dihedral angle between the phenyl and p-tolyl rings is 58.22 (9)°. The 3-acetyl-1H-pyrazole-4-carbonitrile unit is essentially planar, with an r.m.s. deviation of 0.0295 (1) Å for the ten non-H atoms.

3-Methyl-1-benzofuran-2-carbohydrazide

In the asymmetric unit of the title benzofuran derivative, C₁₀H₁₀N₂O₂, there are three crystallograpically independent mol­ecules, which are slightly twisted; the dihedral angle between the benzofuran ring system and the plane of the carbohydrazide unit is 8.64 (11)° in one mol­ecule, whereas the dihedral angles are 9.58 (11) and 6.89 (10)° in the other two mol­ecules. In the crystal, the three independent mol­ecules are linked to each other through N—H...N hydrogen bonds, forming a trimer. The trimers are further linked by weak N—H...O and C—H...O hydrogen bonds into a three-dimensional network. π–π inter­actions with centroid–centroid distances in the range 3.4928 (11)–3.8561 (10) Å are also observed.

(E)-3-Anilino-2-benzoyl-3-(methyl­sulfan­yl)acrylonitrile

In the title acrylonitrile derivative, C₁₇H₁₄N₂OS, the central amino­acryl­aldehyde O=C—C=C—NH unit, wherein an intra­molecular N—H...O hydrogen bond generates an S(6) ring motif, is approximately planar, with an r.m.s. deviation of 0.0234 (2) Å for the five non-H atoms. This plane makes dihedral angles of 41.04 (9) and 84.86 (10)° with the two phenyl rings. The dihedral angle between the two phenyl rings is 54.82 (10)°. An intra­molecular C—H...N hydrogen bond is also present. In the crystal, weak C—H...π and π–π inter­actions, with a centroid–centroid distance of 3.8526 (14) Å, are observed.

(Z)-2-(4-Chloro­benzyl­idene)benzo[d]thia­zolo[3,2-a]imidazol-3(2H)-one

The mol­ecule of the title compound, C₁₆H₉ClN₂OS, is approximately planar, the dihedral angle between the thia­zolo[3,2-a]benzimidazole ring system and the 4-chloro­phenyl ring being 2.10 (5)°. An intra­molecular C—H...S inter­action generates an S(6) ring motif. In the crystal, mol­ecules are stacked into columns along the b axis by π–π inter­actions with centroid–centroid distances of 3.6495 (7)–3.9546 (8) Å.

(1Z,2E)-N′-{1-[2-(4-Bromo­phen­yl)hydrazin-1-yl­idene]-1-chloro­propan-2-yl­idene}thio­phene-2-carbohydrazide

In the title compound, C₁₄H₁₂BrClN₄OS, the thienyl ring is disordered over two orientations with a site-occupancy ratio of 0.853 (2):0.147 (2). The mol­ecule is roughly planar, with the dihedral angles between the thienyl and benzene rings being 6.24 (16) and 9.7 (11)° for the major and minor components, respectively. The central fragment is almost planar [r.m.s. deviation = 0.0275 (2) Å for the ten non-H atoms]. The mean plane through this middle unit makes a dihedral angle of 2.71 (7)° with the benzene ring, whereas these values are 4.46 (15) and 7.7 (11)° for the major and minor components of the thienyl ring, respectively. In the crystal, mol­ecules are linked into dimers by pairs of N—H...O hydrogen bonds, forming R₂²(8) ring motifs. These dimers are arranged into sheets parallel to the ac plane.

(Z)-7-[2-(4-Bromo­phen­yl)hydrazin-1-yl­idene]-6-methyl-3-(pyridin-4-yl)-7H-1,2,4-triazolo[3,4-b][1,3,4]thia­diazine

In the asymmetric unit of the title compound, C₁₆H₁₂BrN₇S, there are two crystallographically independent mol­ecules with similar conformations. Both mol­ecules are slightly twisted; the central 1,2,4-triazolo[3,4-b]-1,3,4-thia­diazine ring system makes dihedral angles of 9.65 (15) and 13.29 (15)° with the pyridine and benzene rings, respectively, in one mol­ecule, whereas the corresponding values in the other mol­ecule are 9.30 (15) and 4.84 (15)°. A weak intra­molecular C—H...N inter­action with an S(6) ring motif is observed in each mol­ecule. In the crystal, the independent mol­ecules are each linked through N—H...N hydrogen bonds and weak C—H...N interactions into ribbons along the c axis. The ribbons are further linked together by weak C—H...N, C—H...π and π–π [centroid–centroid distances = 3.572 (2)–3.884 (2) Å] inter­actions.

1-(4-Fluoro­phen­yl)-2-(phenyl­sulfon­yl)ethanone

In the title compound, C₁₄H₁₁FO₃S, the unit comprising the ethanone and 4-fluoro­phenyl groups is essentially planar, with an r.m.s. deviation of 0.0084 (2) Å for the ten non-H atoms, and it makes a dihedral angle of 37.31 (10)° with the phenyl ring. In the crystal, mol­ecules are linked by pairs of weak C—H...O hydrogen bonds into inversion dimers with R₂²(16) graph-set motifs. The dimers are stacked along the b axis through further C—H...O hydrogen bonds.

2-Phenyl-N′-(2-phenyl­acet­yl)acetohydrazide

In the title compound, C₁₆H₁₆N₂O₂, the N′-acetyl­acetohydrazide group is approximately planar (r.m.s. deviation = 0.018 Å for the eight non-H atoms) and makes dihedral angles of 81.92 (6) and 65.19 (6)° with the terminal phenyl rings. The phenyl rings form a dihedral angle of 62.60 (7)°. In the crystal, mol­ecules are linked into sheets lying parallel to (001) by N—H...O and C—H...O hydrogen bonds. One O atom accepts one N—H...O and one C—H...O hydrogen bond and the other O atom accepts one N—H...O and two C—H...O hydrogen bonds. The N—H...O hydrogen bonds lead to R₂²(8) loops and the C—H...O hydrogen bonds generate R₂¹(6) loops.

6-(4-Bromo­phen­yl)-3-methyl-7H-1,2,4-triazolo[3,4-b][1,3,4]thia­diazine

In the title compound, C₁₁H₉BrN₄S, the 1,2,4-triazole ring is essentially planar (r.m.s. deviation = 0.020 Å) and makes a dihedral angle of 29.1 (5)° with the bromo­benzene ring. The 3,6-dihydro-1,3,4-thia­diazine ring adopts a twist-boat conformation. In the crystal, mol­ecules are linked by C—H...N inter­actions into sheets lying parallel to the (010) plane. The same N atom accepts two such hydrogen bonds.

1-(5-Bromo-1-benzofuran-2-yl)ethanone

The title compound, C₁₀H₇BrO₂, is approximately planar (r.m.s. deviation = 0.057 Å for the 13 non-H atoms). In the crystal, mol­ecules are linked via C—H...O hydrogen bonds into C(5) chains propagating in [100].

2-{2-[(E)-(2-Benzoyl­hydrazin-1-yl­idene)meth­yl]phen­oxy}acetic acid

In the title compound, C₁₆H₁₄N₂O₄, the dihedral angle between the aromatic rings is 12.45 (6)°. The central C(=O)—N—N=C bridge is roughly planar (r.m.s. deviation = 0.0346 Å) and makes dihedral angles of 13.01 (7) and 0.56 (7)° with the attached phenyl and benzene rings, respectively. The acetic acid unit (r.m.s. deviation = 0.0066 Å) is twisted from its attached benzene ring [dihedral angle = 19.48 (6)°]. In the crystal, mol­ecules are linked by O—H...(O,N), N—H...O and C—H...O hydrogen bonds into sheets lying parallel to the bc plane. A weak aromatic π–π stacking inter­action is also observed [centroid–centroid distance = 3.7330 (7) Å].

2-[(1H-Benzimidazol-2-yl)sulfan­yl]-1-phenyl­ethanone

The title compound, C₁₅H₁₂N₂OS, adopts a twisted V-shape, with the S atom as the pivot. The benzimidazole ring system [maximum deviation = 0.015 (1) Å] makes a dihedral angle of 78.56 (7)° with the phenyl ring. The O atom of the ketone group is close to coplanar with its adjacent ring [O—C—C—C torsion angle = 11.0 (2)°]. In the crystal, mol­ecules are linked by N—H...N hydrogen bonds into an infinite chain along [001]. The crystal packing also features a C—H...π inter­action.

1-Chloro-1-[(Z)-2-phenyl­hydrazin-1-yl­idene]propan-2-one

The title compound, C₉H₉ClN₂O, is close to planar (r.m.s. deviation for the non-H atoms = 0.0446 Å); it exists in a cis conformation with respect to the C=N double bond. In the crystal, the ketone O atom accepts both N—H...O and C—H...O hydrogen bonds, which leads to [010] infinite chains incorporating R₂¹(6) loops. The crystal structure also features a C—H...π inter­action.

(Z)-1-(4-Methyl­phen­yl)-2-(phenyl­sulfon­yl)ethanone oxime

The mol­ecule of the title compound, C₁₅H₁₅NO₃S, has a twisted U-shaped conformation: the twist occurs at the central C—S(=O)₂—C—C—C unit and the benzene ring makes a dihedral angle of 28.74 (7)° with the phenyl ring. The S—C—C=N torsion angle is −88.95 (13)°. In the crystal, inversion dimers linked by pairs of O—H...N hydrogen bonds generate R₂²(6) loops, and C—H...O hydrogen bonds connect the dimers into a three-dimensional network.

(N′,N′′Z,N′,N′′E)-N′,N′′-[1-(4-Chloro­phen­yl)ethane-1,2-diyl­idene]bis­(3-methyl-1-benzofuran-2-carbohydrazide)

In the title compound, C₂₈H₂₁ClN₄O₄, the benzofuran ring systems make dihedral angles of 7.43 (8) and 30.92 (9)° with the chloro-substituted benzene ring. The dihedral angle between the two benzofuran ring systems is 27.41 (7)°. The two benzofuran rings are connected to the chloro-substituted benzene ring through C—N—N=C and C—N—N=C—C bridges which are nearly planar [maximum deviations = 0.003 (1) and 0.037 (1) Å]. An intra­molecular N—H...N hydrogen bond generates an S(6) ring motif. In the crystal, mol­ecules are linked by N—H...(O,N) and C—H...O hydrogen bonds into a tape along the c axis and these tapes are further connected by another weak C—H...O hydrogen bond into a sheet parallel to the bc plane. π–π inter­actions [centroid-to-centroid distances = 3.4845 (12)–3.6250 (13) Å] are also observed.

3-(3-Meth­oxy­phen­yl)benzo[d]thia­zolo[3,2-a]imidazol-9-ium hydrogen sulfate

In the title mol­ecular salt, C₁₆H₁₃N₂OS⁺·HSO₄⁻, the thia­zolo[3,2-a]benzimidazolium ring system is roughly planar [maximum deviation = 0.046 (3) Å] and makes a dihedral angle of 58.22 (11)° with the benzene ring. The meth­oxy group is almost coplanar with its attached benzene ring [C_meth­yl—O—C—C = −1.6 (5)°]. In the crystal, the cation is linked to the anion by a bifurcated N—H...(O,O) hydrogen bond, generating an R₁²(4) ring motif. The ion pairs are then connected by a C—H...O hydrogen bond into inversion dimers and these dimers are further linked by O—H...O hydrogen bonds into an infinite tape along [100]. A π–π stacking inter­action [centroid-to-centroid distance = 3.5738 (18) Å] and a short inter­molecular contact [S...O = 2.830 (3) Å] are also observed.

(E)-2-(2,3-Dimethyl­anilino)-N′-(thio­phen-2-yl­methyl­idene)benzohydrazide

In the title compound, C₂₀H₁₉N₃OS, the central benzene ring makes dihedral angles of 45.36 (9) and 55.33 (9)° with the thio­phene ring and the dimethyl-substituted benzene ring, respectively. The dihedral angle between the thio­phene ring and dimethyl-substituted benzene ring is 83.60 (9)°. The thio­phene ring and the benzene ring are twisted from the mean plane of the C(=O)—N—N=C bridge [maximum deviation = 0.0860 (13) Å], with dihedral angles of 23.86 (9) and 24.77 (8)°, respectively. An intra­molecular N—H...O hydrogen bond generates an S(6) ring. In the crystal, mol­ecules are linked by N—H...O and C—H...O hydrogen bonds to the same acceptor atom, forming sheets lying parallel to the bc plane. The crystal packing also features C—H...π inter­actions.

2-(2,3-Dimethyl­anilino)benzohydrazide

In the title compound, C₁₅H₁₇N₃O, the dihedral angle between the benzene rings is 58.05 (9)°. The non-H atoms of the hydrazide group lie in a common plane (r.m.s. deviation = 0.0006 Å) and are close to coplanar with their attached benzene ring [dihedral angle = 8.02 (9)°]. An intra­molecular N—H...O hydrogen bond generates an S(6) ring motif in the mol­ecule, and a short intra­molecular contact (H...H = 1.88 Å) is also observed. In the crystal, mol­ecules are linked by pairs of N—H...N hydrogen bonds into inversion dimers. The crystal packing also features C—H...π inter­actions.

2-Anilino-4-(1,3-benzothia­zol-2-yl)-5-(4-chloro­benzo­yl)thio­phene-3-carbonitrile

In the title compound, C₂₅H₁₄ClN₃OS₂, the central thio­phene ring [maximum deviation = 0.011 (1) Å] makes dihedral angles of 55.72 (5), 13.36 (5) and 46.77 (4)° with the adjacent chloro-substituted benzene ring, the benzene ring and the 1,3-benzothia­zole ring system [maximum deviation = 0.012 (1) Å], respectively. An intra­molecular C—H...S(thienyl) hydrogen bond generates an S(6) ring motif in the mol­ecule. In the crystal, mol­ecules are linked by pairs of N—H...N hydrogen bonds into inversion dimers and the dimers are further connected by C—H...O hydrogen bonds into tapes running along [100]. Aromatic π–π stacking inter­actions are also observed [centroid-to-centroid distances = 3.6116 (6) and 3.7081 (6) Å].

2,3,5-Triphenyl-2H-tetra­zol-3-ium bromide ethanol monosolvate

In the title compound, C₁₉H₁₅N₄⁺·Br⁻·C₂H₅OH, the tetra­zole ring makes dihedral angles of 57.44 (9), 50.92 (9) and 4.65 (8)° with the attached phenyl rings. In the crystal, the cation and the anion are linked to each other by inter­molecular C—H...Br hydrogen bonds into an infinite chain along the b axis. The anion and the ethanol solvent mol­ecule are linked by an O—H...Br hydrogen bond. The crystal studied was an inversion twin with a refined component ratio of 0.632 (5):0.368 (5).

2,3,5-Triphenyl-2H-tetra­zol-3-ium tetra­phenyl­borate

In the title salt, C₁₉H₁₅N₄⁺·C₂₄H₂₀B⁻, the tetra­phenyl­borate anion is in a tetra­hedral geometry around the B atom [C—B—C angles of 107.10 (9)–111.79 (9)°]. In the cation, the tetra­zole ring makes dihedral angles of 3.04 (7), 51.75 (7) and 51.13 (7)° with the attached phenyl rings. In the crystal, C—H...π inter­actions link the cations and anions into ion pairs.

2,3,5-Triphenyl-2H-tetra­zol-3-ium iodide

The asymmetric unit of the title mol­ecular salt, C₁₉H₁₅N₄⁺·I⁻, contains four 2,3,5-triphenyl-2H-tetra­zol-3-ium cations and five iodide anions, with two of the latter lying on crystallographic inversion centres. In each cation, the tetra­zole ring is essentially planar (r.m.s. deviations = 0.004–0.007 Å). The dihedral angles between the tetra­zole ring and its three attached benzene rings in the four independent cations are: 12.9 (4), 67.0 (4), 48.1 (4); 20.8 (4), 51.1 (4), 62.3 (4); 11.4 (4), 52.3 (4), 47.3 (4) and 6.0 (4), 85.7 (4), 43.5 (4)°. A C—H...I hydrogen bond and C—H...π inter­actions are observed in the crystal.

(Z)-2-Benzyl­idenebenzo[d]thia­zolo[3,2-a]imidazol-3(2H)-one

The mol­ecule of the title compound, C₁₆H₁₀N₂OS, is approximately planar, the dihedral angle between the 1,3-benzothia­zolo[3,2-a]imidazol-3(2H)-one and the benzyl­idene moieties being 4.10 (8)°. A weak intra­molecular C—H...S inter­action generates an S(6) ring. No inter­molecular hydrogen bonds are observed in the crystal structure.

1-(1,5-Diphenyl-4-phenyl­sulfonyl-1H-pyrazol-3-yl)ethanone

The asymmetric unit of the title compound, C₂₃H₁₈N₂O₃S, contains two mol­ecules with comparable geometries. In one mol­ecule, the pyrazole ring forms dihedral angles of 61.65 (11), 47.88 (11) and 63.20 (14)° with the three benzene rings. The corresponding values for the other mol­ecule are 77.19 (11), 43.55 (11) and 63.56 (15)°. In the crystal, both mol­ecules are linked into inversion dimers by pairs of C—H...S hydrogen bonds, generating R₂²(14) loops in each case.

3-Oxo-3-(piperidin-1-yl)propane­nitrile

In the title compound, C₈H₁₂N₂O, the piperidine ring exhibits a chair conformation and its least-squares plane (all atoms) makes a dihedral angle of 32.88 (12)° with the propane­nitrile unit (r.m.s. deviation = 0.001 Å). In the crystal, mol­ecules are linked by C—H...O hydrogen bonds, forming chains along [001].

(Z)-2-(5-Acetyl-4-methyl-3-phenyl-2,3-dihydro-1,3-thia­zol-2-yl­idene)-3-(3-methyl-1-benzofuran-2-yl)-3-oxo­propane­nitrile

In the title compound, C₂₄H₁₈N₂O₃S, the benzofuran ring system (r.m.s. deviation = 0.010 Å) forms dihedral angles of 83.13 (17) and 8.92 (14)° with the benzene and thia­zole rings, respectively. The dihedral angle between the benzene and thia­zole rings is 84.51 (19)°. The mol­ecular structure features an intra­molecular C—H...O hydrogen bond, which closes an S(6) ring. There are no inter­molecular hydrogen bonds observed in this structure.