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

Abstract

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-2H-1,2,3-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 E_C(O)NH/E_C=N. Also present in (E)-N^'-((2-phenyl-2H-1,2,3-triazol-4-yl)methylene)isonicotinohydrazide is an interesting R⁴₄(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.

Keywords:
benzotriazoles; hydrazones; acylhydrazones; hydrates; intermolecular interactions

Introduction

1,2,3-Triazole derivatives have found applications in many areas.^1-3 Particularly important uses have been in the medical field, including as antiviral,^4-6 antimalarial,⁷ antitubercular,^8-10 antifungal,^11-13 anti-HIV,¹⁴ β-lactamase inhibition,¹⁵ anti-epileptic,¹⁶ anti-HSV,¹⁷ anti-inflammatory,¹⁸ antimicrobial^19,20 and α-glycosidase inhibition agents.^21-24 A recent α-glycosidase inhibition study involved a number of different 1-phenyl-1H- and 2-phenyl-2H-1,2,3-triazolyl derivatives.²⁴ See Figure 1 for the tautomeric forms of the parent compounds: 1H-1,2,3-triazole and 2H-1,2,3-triazole.

Figure 1
(a) 1H-1,2,3-triazole; (b) 2H-1,2,3-triazole.

The crystal structures of four of the moderately active hydrazonyl derivatives in the glycosidase inhibition study²⁴ have been determined, namely of (Z)-1-phenyl-4-[((2-phenylhydrazono)methyl)]-1H-1,2,3-triazole (1a), (Z)-4-[(2-(2,4-dimethylphenyl)hydrazono)methyl]-2-phenyl-2H-1,2,3-triazole (2a), (E)-4-[(2-(2,4-dinitrophenyl)hydrazono)methyl]-2-phenyl-2H-1,2,3-triazole (2b), and (E)-N^'-((2-phenyl-2H-1,2,3-triazol-4-yl)methylene)isonicotinohydrazide dihydrate, (3·2H₂O), see Scheme 1.

Scheme 1
Preparation of compounds.

An antifungal activity study of related 1H-1,2,3-triazolyl hydrazones was also published very recently.¹³ The crystal structure of one of the compounds, (E)-4-[2-ClC₆H₄-NH-N=CH)-1-(2-ClC₆H₄)-1H-1,2,3-triazole (1b), was reported and has been deposited in the Cambridge Crystallographic Data Centre (CCDC No. 976935; ref code: FONZAL), but only the molecular configuration had been reported in the article.¹³ In this article, we report the crystal structures of 1a, 2a, 2b and (3·2H₂O), and make comparisons with that of 1b.

Experimental

X-Ray crystallography

Data for compounds 1a, 2a and (3·2H₂O) 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 DENZO²⁵ and COLLECT²⁶ 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 2007/2.²⁷ The program, MERCURY²⁸ was used in the preparation of the Figures. SHELXL97²⁹ and PLATON³⁰ 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.³¹ Difference map provided position for the N-H hydrogen atoms in all four compounds and for the water hydrogen atoms in (3·2H₂O). All other hydrogen atoms were placed in calculated positions. Crystal data and structure refinement details are listed in Table 1.

Table 1
Crystal data and structure refinement

	1a	2a	2b	(3.2H2O)
Empirical formula	C15H13N5	C17H17N5	C15H11N7O4	C15H16N6O3
Formula weight	263.30	291.38	353.31	328.34
Temperature / K	100(2)	100(2)	120(2)	100(2)
Crystal system, space group	triclinic, P-1	monoclinic, P21/n	triclinic, P-1	monoclinic, P21/c
Unit cell dimensions
a / Å	5.7096(4)	15.139(7)	9.2315(3)	9.2332(6)
b / Å	7.2055(5)	5.5315(17)	9.5903(5)	11.9186(7)
c / Å	15.7986(11)	17.352(8)	9.6938(6)	14.0316(9)
α / degree	98.715(10	90	89.796(6)	90
β / degree	99.437(10)	94.300(4)	65.000(8)	95.041(7)
γ / degree	90.9490(10)	90	85.248(7)	90
Volume / Å3	633.19(8)	1448.9(10)	774.67(7)	1538.16(17)
Z	2	4	2	4
Density (calculated) / (mg m-3)	1.381	1.336	1.515	1.418
Absorption coefficient / mm-1	0.088	0.084	0.115	0.103
F(000)	276	616	364	688
Crystal size / mm	0.11 × 0.07 × 0.03	0.24 × 0.04 × 0.04	0.96 × 0.53 × 0.23	0.16 × 0.096 × 0.06
θ range for data collection / degree	2.65 to 27.48	3.45 to 27.62	3.10 to 27.43	3.06 to 27.48
Index ranges	-6 ≤ h ≤ 7; -9 ≤ k ≤ 9; -20 ≤ l ≤ 20	-16 ≤ h ≤ 19; -7 ≤ k ≤ 4; -22 ≤ l ≤ 21	-11 ≤ h ≤ 11; -12 ≤ k ≤ 12; -12 ≤ l ≤ 12	-8 ≤ h ≤ 11; -15 ≤ k ≤ 11; -18 ≤ l ≤ 18
Reflections collected	7812	8351	9903	9099
Independent reflections	2856 (Rint = 0.0398)	3306 (Rint = 0.0218)	3511 (Rint = 0.0205)	3511 (Rint = 0.0438)
Reflections observed (> 2sigma)	1959	2891	2982	2481
Data completeness	0.98	0.98	1.00	1.00
Data/restraints/parameters	2856 / 0 / 184	3306 / 0 / 204	3511 / 0 / 238	3511 / 0 / 232
Goodness-of-fit on F2	0.89	1.06	1.10	1.02
Final R indices [I > 2sigma(I)]	R1 = 0.042 wR2 = 0.102	R1 = 0.053 wR2 = 0.116	R1 = 0.035 wR2= 0.097	R1 = 0.043 wR2 = 0.101
R indices (all data)	R1 = 0.071 wR2 = 0.114	R1 = 0.062 wR2 = 0.122	R1 = 0.041 wR2 = 0.105	R1 = 0.066 wR2 = 0.108
Largest diff. peak and hole / (e Å-3)	0.26 and -0.28	0.21 and -0.22	0.24 and -0.23	0.26 and -0.27
CCDC No.	1434781	1434786	1434776	1434783

Results and Discussion

The compounds were prepared as previously reported²⁴ 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 (3·2H₂O).

Molecular conformations

The asymmetric unit in each of 1a, 2a and 2b consists of a single molecule, that of (3·2H₂O) a molecule of 3 and two molecules of water. Figure 2 illustrates the numbering schemes for all the molecules. Selected bond lengths and angles are listed in Table 2. Comparison of the bond lengths in the triazolyl rings in the 1H-1,2,3-triazole, compound 1a, and the 2H-1,2-3-triazole compounds, 2a, 2b and (3·2H₂O), indicate that the major differences are found in the C4-C5 and C5-N1 bond lengths. The bond lengths in the hydrazonyl linker, C13-N5-N4-C6-C4, in compounds 1a, 1b and 2a, indicate that electron delocalization occurs within the link, as do the bond lengths in the acylhydrazonyl linker, C14-C13(O1)-N5-N4-C6-C4, in molecule 3.

Figure 2
Atom arrangements and numbering schemes for (a) 1a, (b) 2a, (c) 2b, and (d) (3^.2H₂O). Ellipsoids are drawn at the 50% level. Hydrogen atoms are drawn as spheres of arbitrary radius. Intramolecular hydrogen bonds are drawn as thin dashed lines.

Table 2
Selected bond lengths (Å) and angles (degree)

	1a	2a	2b	(3.2H2O)
C13-N5	1.4005(18)	1.395(2)	1.3524(14)	1.3519(13)
N5-N4	1.3626(18)	1.3502(18)	1.3757(13)	1.3772(15)
N4-C6	1.2940(19)	1.295(3)	1.2812(14)	1.2769(18)
C6-C4	1.455(2)	1.446(3)	1.4551(15)	1.4494(18)
C4-C5	1.377(2)	1.403(3)	1.4031(16)	1.397(2)
C5-N1	1.3466(19)	1.323(3)	1.3245(16)	1.3245(16)
N1-N2	1.3600(17)	1.3452(17)	1.3449(13)	1.3429(16)
N2-N3	1.3155(17)	1.339(2)	1.3550(13)	1.3318(15)
N3-C4	1.375(2)	1.346(2)	1.3384(14)	1.3342(18)
C13-N5-N4	118.14(12)	119.79(14)	118.97(9)	117.58(12)
N5-N4-C6	118.39(15)	118.44(15)	115.19(10)	116.68(12)
N4-C6-C4	129.14(15)	129.27(15)	118.73(10)	118.03(13)
C18-C13-N5-N4	21.9(2)	1.3(2)	8.82(17)
C15-C14-C13-N5				8.2(2)
C18-C14-C13-N5				173.02(13)
C15-C14-C13-O1				171.29(13)
C18-C14-C13-O1				7.5(2)
C14-C13-N5-N4	159.39(14)	179.36(15)	172.05(11)	179.94(11)
C13-N5-N4-C6	177.85(13)	179.16(16)	177.03(11)	175.48(13)
N5-N4-C6-C4	1.4(2)	0.2(3)	176.56(11)	179.05(12)
N4-C6-C4-N3	1.8(3)	2.4(3)	179.51(12)	176.87(13)
N4-C6-C4-C5	178.51(15)	176.1(2)	0.7(2)	1.1(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 (3·2H₂O) (Figure 2); compound 1b¹³ 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). In Figure 3b 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.

Figure 3
(a) The (E)-geometric form determined for 1b in the solid state;¹³ (b) potential (Z)-forms of 1b. Ar = 2-chlorophenyl.

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 bond (E_C=N and Z_C=N), making four possible arrangements in all about the C(O)-NH-N=CH-aryl fragment.^32-35

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-1,2,3-triazolyl 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 phenyl groups and the triazolyl ring are very similar to the single dihedral angle between the two phenyl rings in each of 1a, 2a, 2b and 3, which indicates that the deviation from planarity can be considered to have arisen from rotations about the C13-N5 and C7-N2 bonds occurring in the same sense. This is not the case in the 1H-1,2,3-triazolyl compound, 1b. For 1b, the dihedral angles point to rotations about the C13-N5 and C7-N2 bonds occurring in the opposite senses, with the result that the two phenyl groups have a small dihedral angle of ca. 6º, compared to ca. 51º in 1a. If rotations about these C13-N5 and C7-N2 bonds did occur in the same sense, it would place either Cl1 too close to N5, or Cl2 too close to N2.

Table 3
Angles between the best planes through the aryl rings

Compound	Angle between free phenyl and triazole / degree	Angle between free phenyl and phenyl on triazole / degree	Angle between triazole andattached phenyl / degree
1a	23.72(8)	51.15(7)	28.54(8)
2a	2.58(9)	7.13(8)	4.64(9)
2b	14.06(7)	8.66(6)	6.92(7)
(3.2H2O)	6.35(7)	11.19(7)	5.28(7)
1b 13	23.34(8)	6.57(8)	27.67(8)

Figure 4
Molecular conformations. Hydrogen atoms have been omitted.

Dihedral angles between aryl and triazolyl rings in 1-aryl-1H- and 2-aryl-2H-1,2,3-triazole compounds have been shown to vary considerably, for example, such angles are 0.34(17) and 87.1(2)º, respectively, in 4-(difluoromethyl)-1H-1,2,3-triazole,³⁶ and in one independent molecule of 1-[5-methyl-1-(4-nitrophenyl)methyl-1-(4-methylphenyl)-1H-1,2,3-triazol-4-yl]ethanone.³⁷ The aryl group substituents and crystal packing effects have major influences on such dihedral angles. The dihedral angles in 2a between the phenyl group and (i) the attached ortho-nitro group, O2-N6-O1, and (ii) para-nitro group, O3-N7-O4, are 3.93 and 13.69º, respectively. The small angle between the phenyl and its ortho-nitro group facilitates the formation of the N5-HN5···O1 intramolecular hydrogen bond.

Crystal structures

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).³⁸

Table 4
Geometric parameters (Å, degree) for intra- and intermolecular interactions

Intramolecular hydrogen bonds
Compound	D-H···A	D-H	H···A	D···A	D-H···A
1a	N5-HN5···N3	0.949(17)	2.067(17)	2.7829(18)	131.0(14)
2a	N5-HN5···N3	0.929(17)	2.042(17)	2.768(2)	133.9(15)
2a	C8H8···N1	0.95	2.49	2.808(3)	100
2b	N5-HN5···O1	0.898(14)	1.975(14)	2.6342(14)	129.1(14)
2b	N5-HN5···N6	0.898(14)	2.621(16)	2.9512(15)	102.7(11)
2b	C18-H18···N4	0.95	2.40	2.7320(16)	100
(3⋅2H2O)	C12-H12···N3	0.93	2.50	2.8069(18)	100
Intermolecular hydrogen bonds
Compound	D-H···A	D-H	H···A	D···A	D-H···A
2b	N5-HN5···O1i	0.898(14)	2.520(15)	3.3218(14)	149.0(14)
2b	C5-H5···O3ii	0.95	2.53	3.3984(18)	152
2b	C6-H6···O3iii	0.95	2.60	3.0389(15)	109
2b	C6-H6···O2i	0.95	2.60	3.5082(15)	160
2b	C11-H11···O4iv	0.95	2.52	3.2179(18)	130
(3⋅2H2O)	OW2-HW1A···O1	0.836(18)	2.072(18)	2.8281(150	150.2(17)
(3⋅2H2O)	OW2-HW1A···N4	0.836(18)	2.562(19)	3.2512(16)	140.6(15)
(3⋅2H2O)	OW2-HW1B···OW1	0.959(18)	1.773(18)	2.7198(16)	168.5(16)
(3⋅2H2O)	N5-HN5···OW2v	0.869(18)	2.048(18)	2.8974(17)	165.6(14)
(3⋅2H2O)	OW1-HW2A···OW2vi	0.787(18)	2.119(18)	2.8742(16)	161.0(18)
(3⋅2H2O)	OW1-HW2B···N8vii	0.886(18)	1.975917)	2.8457(17)	167.2(16)
(3⋅2H2O)	C6-H6···OW2v	0.93	2.55	3.3076(18)	138
(3⋅2H2O)	C9-H9···OW1viii	0.93	2.56	3.4728(19)	169
(3⋅2H2O)	C15-H15···OW2v	0.93	2.52	3.3985(18)	158
Symmetry codes: i = 1 - x, 1 - y, -1 - z; ii = 1 - x, 2 - y, -z; iii = x, y, -1 + z; iv = -1 + x, 1 + y, -1 + z; v = -x, -½ + y, ½ + z; vi = -x, 1 - y, 1 - x; vii = 1 + x, ½ - y, ½ + z; viii = 1 - x, y, z.
Y-X···π interactionsa
Compound	Y-X···Cga	X···Cg	Xperp	γ	Y-X···Cg	Y···Cg
1a	C9-H9···Cg3i	2.68	2.67	5.81	131	3.3796(17)
1a	C12-H12···Cg3ii	2.63	2.62	6.29	131	3.3403(16)
1a	C15-H15···Cg2iii	2.78	2.75	8.72	131	3.4822(17)
1a	C18-H18···Cg2iv	2.76	2.72	10.36	129	3.4370(16)
2a	C19-H19B···Cg2v	2.81	2.68	17.59	150	3.692(2)
2b	N7-O4···Cg2vi	3.7402(11)	3.37	25.73	74.54(6)	3.6125(12)
Symmetry codes: i = -x, 1 - y, 1 - z; ii = 1 - x, 2 - y, 1 - z; iii = -x, 2 - y, 1 - x; iv = 1 - x, 1 - y, 1 - z; v = x, 1 + y, z; vi = 1 - x, 2 - y, -1 - z.
π···π interactionsa
Compound	Cg(I)···Cg(J)	Cg···Cg	α	β	γ	CgIperp	CgJperp
1a	Cg1···Cg1i	4.2304(9)	0.02	34.8	34.8	3.48	3.475
2a	Cg1···Cg2ii	3.726(2)	4.58(9)	27.4	22.8	3.4350(7)	3.3089(6)
2a	Cg2···Cg1ii	3.726(2)	4.58(9)	22.8	27.4	3.3089(6)	3.4350(7)
2a	Cg3···Cg1iii	4.065(2)	2.64(9)	33.3	30.7	3.493597)	3.3986(7)
2b	Cg1···Cg1iv	3.8953(8)	0.03	32.4	32.4	3.27	3.265
2b	Cg2···Cg3v	4.0523(9)	8.66	30.4	36.7	3.25	3.294
2b	Cg3···Cg1v	3.8968(7)	14.05	26.6	26.2	3.50	3.484
(3⋅2H2O)	Cg1···Cg2vi	3.5089(8)	5.28	12.6	7.5	3.48	3.425
(3⋅2H2O)	Cg1···Cg2vii	3.9188(8)	8.00	32.3	36.0	3.17	3.314
(3⋅2H2O)	Cg3···Cg2vii	3.9611(8)	14.12	44.0	23.8	3.63	3.246
Symmetry operation: i = 1 - x, 1 - y, 1 - z; ii = 1 - x, -y, 1 - z; iii = x, 1 + y, z; iv = -x, 2 - y, -1 - z; v = 1 - x, 2 - y, -1 - z; vi = 1 + x, y, z; vii = 1 + x, ½ - y, ½ + z.

• ^a
  In compounds 1a and 2b, Cg1, Cg2 and Cg3 are the centroids of the ring containing N2, C10 and C16, respectively; in compound 3, Cg1, Cg2 and Cg3 are the centroids of the ring containing N2, C16 and C10, respectively; in compound 2a, Cg1, Cg2, Cg3, Cg4, Cg5 and Cg6 are the centroids of the ring containing N2A, C10A, C16A, N2B, C10B and C16B, respectively; β is the angle between the vectors Cg···Cg and CgIperp, where CgIperp is the perpendicular distance of CgI from the plane of ring J. Similarly, γ is the angle between the vectors Cg···Cg and CgJ_perp. CgJ_perp is the perpendicular distance of CgI from the plane of ring I.

The combination of the C-H···π interactions, C9-H9···π(phenyl-b), C12-H12···π(phenyl-b), C15-H15···π(phenyl-a) and C18-H18···π(phenyl-a), provides sheets of molecules in the ab plane, as shown in Figure 5. Phenyl-a and phenyl-b are the phenyl groups with atoms C7-C12 and C13-C18, respectively. The triazole ring is not involved in C-H···π interactions. The PLATON analysis³¹ indicates the possibility of π(triazolyl)···π(triazolyl) stacking interactions.³⁹ However, although the perpendicular distance between parallel triazole rings is only 3.475 Å, the Cg···Cg distance is large at 4.2304(9) Å, resulting in ring offsets of 2.413 Å, which indicates that the triazole rings do not overlap.

Figure 5
Compound 1a. Part of the sheet of molecules obtained from C9-H9···π(phenyl-a), C12-H12···π(phenyl-a), C15-H15···π(phenyl-b) and C18-H18···π(phenyl-b) in the ab plane; phenyl-a and phenyl-b are the free and triazole-bound phenyl, respectively.

Compound 2a

The major intermolecular interactions in 2a are π···π stacking interactions. Dimers are generated from pairs of π(triazole)···π(phenyl-a) interactions. These dimeric units are further linked by π(triazole)···π(phenyl-b) and by C-H···π(phenyl-a) interactions into two molecule wide columns, where phenyl-a and phenyl-b refer to the phenyl group attached to the triazole and the other phenyl group, respectively (Figure 6a). These two-molecular wide columns are free standing and so 2a has a one-dimensional structure. As shown in Figure 6b, such columns of molecules are propagated in different directions, with angles between the best planes of ca. 76º.

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.

Compound 2b

As well as the classical intramolecular N-H···O hydrogen bond, there is also a classical intermolecular N-H···O hydrogen bond, and weaker intermolecular C-H···O hydrogen bonds, π···π stacking and N-O···π interactions (Table 4).^40,41 In the following discussion, the overall structure is broken down into three sub-structures. Firstly, pairs of the classical intermolecular N5-HN5···O1 and weaker C11-H11···O4 hydrogen bonds form centrosymmetric dimers, as shown in Figure 7a. Included within these dimers are intramolecular N5-HN5···O1 hydrogen bonds: together, these hydrogen bonds generate a set of R²₂(8), R²₂(4) and R²₂(8) rings. The O1···O1 distance in the O1-NH5-O1-NH5 ring is short. Secondly, ladders of molecules, containing R²₂(24) and R⁴₂(24) rings,⁴² are generated from the combination of C5-H5···O3 and C6-H6···O3 hydrogen bonds: in these ladders, the C5-H5···O3 hydrogen bonds form the rings of the ladder and the C6-H6···O3 form the sides (see Figure 7b). The third sub-structure is a sheet of molecules generated from π(triazole)···π(nitrophenyl), π(phenyl)···π(nitrophenyl) and π(triazole)···π(triazole) stacking interactions, N7-O4···π(phenyl) and C11-H11···O4 hydrogen bonds. The π(triazole)···π(nitrophenyl), π(phenyl)···π(nitrophenyl) and N7-O4···π(phenyl) interactions generate dimeric units, which are linked into single-molecule wide columns by the π(triazole)···π(triazole) interactions. These single-molecule wide columns are further linked into bi-molecule wide columns by the C11-H11···O4 hydrogen bonds (see Figure 7c). Overall, a three-dimensional array is produced.

Figure 7
Compound 2b. (a) A centrosymmetric dimer generated from pairs of N5-HN5···O1 and C6-H6···O2 intermolecular hydrogen bonds: also indicated are intramolecular N5-HN5···O1 hydrogen bonds, together these hydrogen bonds generate a set of R²₂(8), R²₂(4) and R²₂(8) rings; (b) ladders of molecules, containing R²₂(24) and R⁴₂(24) rings, are generated from the combination of C5-H5···O3 and C6-H6···O3 intermolecular hydrogen bonds; (c) part of a sheet of molecules generated from π(triazole)···π(nitrophenyl), π(phenyl)···π(nitrophenyl), π(triazole)···π(triazole) and N7-O4···π(phenyl) interactions and C11-H11···O4 intermolecular hydrogen bonds. Intermolecular interactions are drawn as thin dashed lines. Symmetry operations are listed in Table 4.

Compound (3·2H₂O)

The intermolecular interactions in compound (3·2H₂O) are π···π stacking interactions and O-H···X (X = O and N), N-H···O and C-H···O hydrogen bonds (Table 4). As expected, the two water molecules are strongly involved in the supramolecular arrangements. A sheet containing molecules of 3 and water, with oxygen atom, OW1, is generated from combinations of π(triazolyl)···π(phenyl), π(triazolyl)···π(pyridinyl) and π(phenyl)···π(pyridinyl) interactions, and C9-H9···OW1 and OW1-HW2B···N8 hydrogen bonds, as illustrated in Figure 8a. Molecules in each layer of the sheet are linked by C9-H9···OW1 and OW1-HW2B···N8 hydrogen bonds, and layers are linked by the three different π···π interactions. The two water molecules make very different connections to other molecules, as shown in Figures 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 (3·2H₂O) is the R⁴₄(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.

Figure 8
Compound (3·2H₂O). (a) A sheet of 3 and hydrate molecules (with OW1) is generated from combinations of π(triazolyl)···π(phenyl), π(triazolyl)···π(pyridinyl) and π(phenyl)···π(pyridinyl) interactions, and C9-H9···OW1 and OW1-HW2B···N8 hydrogen bonds; (b) and (c) short contacts to the hydrate molecules, HW1A-OW2-HW2A and HW2A-OW1-HW2B, respectively; (d) a R⁴₄(8) ring generated from four hydrate molecules, showing contacts with molecules 3; (e) packing of the molecules looking down the c-axis. Table 4 lists the symmetry operations. The intermolecular interactions are drawn as thin dashed lines.

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 (3·2H₂O).

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 1a and 2a arise from the stabilizing presence of intramolecular N5-HN5···N3 hydrogen bonds, while in 2b the presence of intramolecular N5-HN5···O1 hydrogen bonds, in lieu of potential N5-HN5···N3 hydrogen bonds, reinforces the (E)-geometry. An E_C(O)NH/E_C=N arrangement about the C(O)-NH-C=N fragment, and an interesting R⁴₄(8) ring composed of four hydrate molecules, are features of the crystal structure of the hydrated acylhydrazone, (3·2H₂O).

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-1,2,3-triazole 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, 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.

Supplementary Information

Full details of the crystal structure determinations in cif format are available in the online version as Supplementary 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 (3·2H₂O), respectively. Copies of these can be obtained free of charge on written application to CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (fax: [phone]); on request by e-mail to [e-mail] or by access to http://www.ccdc.cam.ac.uk.

https://minio.scielo.br/documentstore/1678-4790/S7WHPdd6zzRGHGdbH8SPNdf/a243f39d125772868561bbd7811fea6584cc8805.pdf

Acknowledgments

The use of the NCS crystallography service at Southampton and the valuable assistance of the staff there are gratefully acknowledged. JLW thanks FAPERJ and CNPq (Brazil) for support. SMSVW and JLW thank PhD John N. Low for discussions.

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Publication Dates

• Publication in this collection
  Dec 2016

History

• Received
  24 Nov 2015
• Accepted
  27 Apr 2016