Crystal Structures of 1-Aryl-1 Hand 2-Aryl-2 H-1 , 2 , 3-triazolyl Hydrazones . Conformational Consequences of Different Classical Hydrogen Bonds

The crystal structures of (Z)-1-phenyl-4-[((2-phenylhydrazono)methyl)]-1H-1,2,3-triazole, (Z)-4-[(2-(2,4-dimethylphenyl)hydrazono)methyl]-2-phenyl-2H-1,2,3-triazole, (E)-4-[(2(2,4-dinitrophenyl)hydrazono)methyl]-2-phenyl-2H-1,2,3-triazole, and (E)-N-((2-phenyl-2H1,2,3-triazol-4-yl)methylene)isonicotinohydrazide dihydrate are reported. The formations of (Z)configurations about the C=N bonds in the first two compounds arise from the stabilizing presence of intramolecular N−H···N hydrogen bonds, while in the third compound, the presence of intramolecular N−H···O hydrogen bonds promotes an (E) geometry. The arrangement about the CONHC=N fragment in the hydrated acylhydrazone is EC(O)NH/EC=N. Also present in (E)-N-((2phenyl-2H-1,2,3-triazol-4-yl)methylene)isonicotinohydrazide is an interesting R4(8) ring formed from hydrogen bonds generated from four water molecules. Significant π···π stacking interactions are exhibited in three compounds, but not in the least planar first compound, in which the dominant intermolecular interactions are C−H···π interactions. Other intermolecular interactions in one of the compounds are C−H···π interactions, in another compound are C−H···O hydrogen bonds and N−O···π interactions, and in the last compound are O−H···X (X = O and N), N−H···O and C−H···O hydrogen bonds.


X-Ray crystallography
Data for compounds 1a, 2a and (3 .2H 2 O) were obtained at 100(2) K, while data for compound 2b were collected at 120(2) K.All with Mo Kα radiation by means of a Rigaku Saturn 724+ (2 × 2 bin mode) instrument of the National Crystallography Service (NCS), University of Southampton.Data collection, data reduction and unit cell refinement were achieved with the DENZO 25 and COLLECT 26 programs.Correction for absorption was achieved in each case by a semi-empirical method based upon the variation of equivalent reflections with the Rigaku version of the program SADABS 2007/2. 27The program, MERCURY 28 was used in the preparation of the Figures.SHELXL97 29 and PLATON 30 were used in the calculation of molecular geometry.The structures were solved by direct methods by SHELXT and fully refined by means of the SHELXL using OSCAIL. 31Difference map provided position for the N−H hydrogen atoms in all four compounds and for the water hydrogen atoms in (3 .2H 2 O).All other hydrogen atoms were placed in calculated positions.Crystal data and structure refinement details are listed in Table 1.

Results and Discussion
The compounds were prepared as previously reported 24 from the corresponding aldehydes, see Scheme 1.Samples used in the structure determinations were grown by slow evaporation of solutions in methanol for 1a and 2a, in 2-methoxyethanol for 2b, and in ethyl acetate for 3.The cell dimensions for a sample of 2b, recrystallized from methanol, indicated the same phase as obtained from 2-methoxyethanol.The crystals obtained from recystallisation of 3 from ethyl acetate were of the dihydrate

Molecular conformations
The asymmetric unit in each of 1a, 2a and 2b consists of a single molecule, that of (3•2H 2 O) a molecule of 3 and two molecules of water.Figure 2  The most significant conformational result is that compounds 1a and 2a have (Z) geometries about the C=N bond, in contrast to the (E)-configuration in 2b and (3•2H 2 O) (Figure 2); compound 1b 13 also has the (E)-configuration (Figure 3a).Generally in the absence of special circumstances, (Z)-isomers are thermodynamically less stable than (E)-isomers.The special circumstances in 1a and 2a must be the formations of the classical and strong N5−HN5•••N3 intramolecular hydrogen bonds, which enhance the stability of the (Z)-isomers.On the other hand, the (E)-configuration in the 2,4-dinitrophenyl derivative, 2b does permit the formation of strong classical N4−HN5•••O1 intermolecular hydrogen bonds, involving an oxygen atom of the ortho-nitro group.Such a strong N4−HN5•••O1 intermolecular hydrogen bond in 2b must further enhance the stability of the (E)-configuration of 1b over that of the (Z)-isomer.For compound 1b, it is argued that the ortho-chloro substituent prevents the formation of a (Z)-configuration, due to the potential steric hindrance between chlorine and adjacent atoms (see Figure 3b).][34][35] While the triazolyl ring is planar in all compounds, none of the compounds is planar overall.The deviation from planarity is relatively small for the 2H-1,2,3-triazolyl compounds, 2a, 2b and 3, as shown by the angles between the aryl rings in Table 3, and very much larger for 1a and 1b (see Figure 4).The increased deviation from planarity of the triazole and its attached phenyl ring in a H-1,2,3triazolyl may arise from steric repulsions between the ortho C−H bonds in the triazole ring and the phenyl ring.Of interest, the sums of the dihedral angles between the

Compound 1a
The only classical hydrogen bond present in 1a is the intramolecular N5−HN5•••N3 hydrogen bond (Figure 2a).The intermolecular interactions in 1a are four C−H•••π interactions (Table 4). 38he combination of the C−H        4). 40,41In the following discussion, the overall structure is broken down into three sub-structures.7c).Overall, a three-dimensional array is produced.
The intermolecular interactions in compound (3 .4).As expected, the two water molecules are strongly involved in the supramolecular arrangements.A sheet containing  8b and 8c.There are seven short contacts to the water molecule, HW1A−OW2−HW2A (Figure 8b), but there are only four short contacts to the other water molecule, HW2A−OW1−HW2B (Figure 8c).Such contacts to the watermolecules generate various rings of atoms.However, the most interesting ring present in (3 .2H 2 O) is the R 4 4 (8) ring generated from four water molecules, two of each HW1A−OW2−HW2A and HW2A-OW1-HW2B, see Figure 8d.As shown in Figure 8d, the water molecules in the tetrameric rings make short contacts with various atoms in 3. Overall, a three-dimension array is formed, see Figure 8e.

Conclusions
The significance of the classical intramolecular hydrogen bonds in the molecular conformations is very pronounced in this study.The formations of (Z)-configurations about the C=N bonds in As found in this study, significant π•••π interactions are exhibited by compounds 2a and 2b, but not by the least planar molecule, 1a.In contrast, the only important intermolecular interactions in 1a are C−H•••π interactions.Are these differences between 1a, on one hand, and 2a and 2b, on the other, consequences of compound 1a being an 1H-1,2,3-triazole compound, while 2a and 2b are 2H-1,2,3triazole derivatives?To effectively answer these questions, further structures of related hydrazonyl derivatives of 1,2,3-triazoles need to be determined.
Moreover, there appears to be no obvious reason why 1a cannot adopt a near planar configuration.Other points to be considered are the influences of steric effects or the position of substituents.Compound 1a has no substituents in either the two phenyl rings, while both 2a and 2b have ortho-and para-substituents in the phenyl ring (C13-C18).The other 1H-1,2,3-triazole compound mentioned in this article, 1b, 13 has ortho chloro substituents in both phenyl rings, and does exhibit a much smaller dihedral angle between the two phenyl rings than does 1a, but is still not planar (Table 3).As in 1a,  these can be obtained free of charge on written application to CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (fax: +44 1223 336033); on request by e-mail to deposit@ccdc.cam.ac.uk or by access to http://www.ccdc.cam.ac.uk.
are drawn the two possibilities for (Z)-(1b), arising from the two possible positions of the chloro group in the phenyl ring.The chlorine atom would be uncomfortably close in (i) to the N−H bond and in (ii) to a nitrogen atom.The arrangement about the C(O)−NH−N=CH-aryl fragment in 3 is designated as E C(O)NH /E C=N .As reported for many acylhydrazones, such as 3, there are two potential configurations about the C(O)−NH bond (E C(O)NH and Z C(O)NH ), as well as the two geometric isomers about the C=N
The hydrogen bonding interactions between the water molecules and molecule of 3 clearly stabilize the E C(O)NH /E C=N arrangement about the C(O)−NH−N=CH-aryl fragment in (3 .2H 2 O).

Figure 6 .
Figure 6.Compound 2a.(a) Part of a two-molecular wide column of molecules of 2a generated from π(triazole)•••π(phenyl-a), π(triazole)•••π(phenyl-b) and by C−H•••π(phenyl-a) interactions, where phenyl-a and phenyl-b refer to the phenyl group attached to the triazole and the other phenyl group, respectively; (b) a view, looking down the a-axis of the orientations of the different columns passing through the unit cell.
no π•••π interactions are exhibited by 1b, but the number of different C−H•••π intermolecular interactions is reduced to one.The most important intermolecular interaction in 1b is the classical intermolecular N(hydrazine)−H•••N(triazole) hydrogen bonds, with less important interactions being C−H•••Cl and N(hydrazine)−H•••Cl hydrogen bonds.This prompts the question: does the presence of substituents in the phenyl rings reduce or even prevent C−H•••π interactions in 2a and 2b, which thus results in different sets of intermolecular interactions being taken up?The answer awaits further study.Information, at http://jbcs.sbq.org.br, and have also been deposited with the Cambridge Crystallographic Data Centre with deposition numbers, 1434781, 1434786, 1434776 and 1434783 for 1a, 2a, 2b and (3 .2H 2 O), respectively.Copies of

Table 1 .
Crystal data and structure refinement

Table 3 .
Angles between the best planes through the aryl rings