1-(2-Amino­phenyl)-3-(4-pyridyl)prop-2-en-1-one: a three-dimensional framework structure built from N—H...N, C—H...O and C—H...π(arene) hydrogen bonds

The intra­molecular dimensions of the title compound, C₁₄H₁₂N₂O, provide evidence for a polarized electronic structure. The mol­ecule, which is almost completely planar, contains an intra­molecular N—H...O hydrogen bond, and the mol­ecules are linked by a combination of N—H...N, C—H...O and C—H...π(arene) hydrogen bonds to form a three-dimensional framework structure.

S1. Comment

Chalcones (1,3-diarylpropenones) are very versatile synthetic intermediates (Awad et al., 1960; Carrie & Rochard, 1963; Coudert et al., 1988; Insuasty et al., 1992, 1997; Kolos et al., 1996). We report here the molecular and supramolecular structure of the title compound, (I) (Fig. 1), which we compare with the structure of the related compound 1-(6-amino-1,3-benzodioxol-5-yl)-3-(4-pyridyl)prop-2-en-1-one, (II) (Cuervo et al., 2007), which is itself closely related to the series of compounds (III)–(V) (Low et al., 2004) and (VI) (Low et al., 2002) (see scheme). 2-Aminochalcones are key intermediates in the synthesis of 6,7-methylenedioxytetrahydroquinolin-4-ones, compounds with interesting biological and pharmacological properties (Prager & Thredgold, 1968; Donnelly & Farell, 1990; Kurasawa et al., 2002), while more generally, many compounds, both synthetic and naturally occurring, containing the 1,3-dioxolyl group are of importance because of their pharmacological properties (Krause & Goeber, 1972; Schlunke & Egli, 1972; Ohta & Kimoto, 1976; Ma et al., 1987; Gabrielsen et al., 1992).

Compound (I) crystallizes in space group C2/c with Z' = 1, whereas the closely related compound (II) crystallizes with Z' = 2 in space group P1, where the pattern of hydrogen bonding clearly rules out any possibility of additional crystallographic symmetry (Cuervo et al., 2007). The molecule of (I) is very nearly planar, as indicated by the key torsion angles (Table 1). For the molecular fragment between atoms C11 and N34 (Fig. 1), the maximum deviations from the mean plane through the non-H atoms are 0.069 (2) Å for atom O1 and 0.050 (2) Å for atom C11. The dihedral angle between this plane and that of the C11–C16 ring is only 8.62 (9)°. As in compounds (II)–(VI) (Cuervo et al., 2007; Low et al., 2004), there is an intramolecular N—H···O hydrogen bond in (I), forming an S(6) motif (Bernstein et al., 1995), and this may have some influence on the overall molecular conformation.

A more significant factor influencing the conformation of (I) may be the electronic polarization indicated by the intramolecular distances (Table 1). Within the C11–C16 ring, the C13—C14 and C15—C16 distances are significantly shorter than the other C—C distances, indicating some degree of o-quinonoid bond fixation. In addition, the exocyclic bonds C12—N12 and C11—C1 are both short for their types [mean values (Allen et al., 1987) 1.355 and 1.488 Å, respectively; lower quartile values 1.340 and 1.468 Å, respectively]. Similar patterns were observed for the C—C and C—N distances in each of (II)–(VI) (Cuervo et al., 2007; Low et al., 2002, 2004). However, the distance C1—O1 distance in (I) is not particularly long compared with those in (II)–(VI), which range from 1.237 (2) to 1.253 (2) Å with a mean of 1.245 Å for ten independent values [compounds (II), (V) and (VI) all crystallize with Z' = 2, while there are two polymorphs of (IV), one monoclinic and the other triclinic, with Z' = 1 and 2, respectively]. These observations indicate the charge-separated form (Ia) as a significant contributor to the overall electronic structure. Form (Ia) is certainly consistent with the near coplanarity observed between the C11–C16 ring and the rest of the molecular structure, despite the rather short intramolecular H2···H16 distance of only 2.04 Å. By way of comparison, the corresponding intramolecular distance involving the pyridyl ring, H2···H32, is somewhat longer at 2.26 Å, even though the pyridyl ring is effectively coplanar with the spacer unit containing atoms C1–C3. It is tempting, therefore, to interpret the orientation of the C11–C16 ring in terms of the competing effects of the intramolecular hydrogen bond and the electronic polarization on the one hand, and a repulsive intramolecular H···H contact on the other.

The molecules of (I) are linked by N—H···N, C—H···O and C—H···π(arene) hydrogen bonds, the first two of which are almost linear (Table 2). It is convenient to consider as the basic building block in the hydrogen-bonded structure the cyclic centrosymmetric R²₂(14) dimer unit built from paired C—H···O hydrogen bonds (Fig. 2). The reference dimer is centred at (1/2, 1, 1/2) and is directly linked, by means of N—H···N hydrogen bonds, to four further dimers, centred at (0, 1/2, 0), (0, 3/2, 0), (1, 1/2, 1) and (1, 3/2, 1), so forming a sheet lying parallel to (101) (Fig. 3). In addition to the S(6) rings, the sheet contains equal numbers of centrosymmetric large and small rings, arranged alternately in a chess-board fashion. The small rings are of R²₂(14) type. If the large rings are taken to include the intramolecular hydrogen bond, then they are of R⁸₁₀(38) type, otherwise they are of R⁶₆(42) type. The C—H···π(arene) hydrogen bond links a pair of molecules related by a twofold rotation axis into another type of cyclic dimer (Fig. 4). The effect of this cyclic motif is to link each (101) sheet to the two adjacent sheets, so linking the molecules into a continuous three-dimensional framework structure.

It is of interest briefly to compare the hydrogen-bonded structure of (II) (Cuervo et al., 2007) with that reported here for (I). The close similarity between the molecular constitutions of (I) and (II) might have been expected to lead to some similarities in their modes of intermolecular aggregation but in fact the aggregation in (I) and (II) is very different. As noted above, (II) crystallizes with Z' = 2, and each of the two independent molecules is linked by a combination of N—H···N and C—H···O hydrogen bonds, just as in (I), although C—H···π(arene) hydrogen bonds are absent from the structure of (II). However, each of the independent molecules forms an independent substructure, with no hydrogen bonds between molecules of the two types. More striking is the difference between the two substructures: one consists of a chain of edge-fused R²₂(14) and R⁴₆(16) rings, while the other consists of sheets containing equal numbers of S(6) and R⁴₅(33) rings (Cuervo et al., 2007). Thus, the only point of similarity between the hydrogen-bonded structures of (I) and (II) lies in the formation of centrosymmetric R²₂(14) rings containing paired C—H···O hydrogen bonds, as formed by (I) and by one of the molecular types in (II). It is thus worth emphasizing that the molecular constitutions of (I) and (II) differ only by the presence in (II) of a fused dioxolane ring, which does not occupy any of the hydrogen-bonding sites utilized in (I). While this additional ring participates in the sheet formation in (II), it plays no role in the formation of the chain of edge-fused rings. This chain in (II) is built from two hydrogen bonds, one each of N—H···N and C—H···O types, which utilize exactly the same atoms as donors and acceptors as those in (I), except that these hydrogen bonds are mediated by different symmetry operators in the two compounds, consequent upon their different space groups.

S2. Experimental

A mixture of 2'-aminoacetophenone (2.8 mmol), pyridine-4-carbaldehyde (2.8 mmol), ethanol (10 ml) and 20% aqueous sodium hydroxide solution (0.5 ml) was heated under reflux for 20 min. The mixture was cooled to ambient temperature, and the resulting solid precipitate was collected by filtration, washed successively with ethanol (2 × 0.5 ml) and water (2 × 0.5 ml), and finally dried under reduced pressure to yield the title compound as an orange solid (yield 82%, m.p. 440 K). MS (70 eV) m/z (%): 224 (23) [M⁺], 223 (12), 195 (8), 146 (100). Crystals of (I) suitable for single-crystal X-ray diffraction were grown by slow evaporation, at ambient temperature and in air, of a solution in ethanol.

S3. Refinement

All H atoms were located in difference maps and then treated as riding. H atoms bonded to C atoms were permitted to ride in geometrically idealized positions, with C—H = 0.93 Å and U_iso(H) = 1.2U_eq(C). The H atoms bonded to atom N12 were permitted to ride at the positions deduced from the difference maps, with U_iso(H) = 1.2U_eq(N), giving N—H = 0.88 Å.

Computing details

Data collection: COLLECT (Nonius, 1999); cell refinement: DIRAX/LSQ (Duisenberg et al., 2000); data reduction: EVALCCD (Duisenberg et al., 2003); program(s) used to solve structure: SIR2004 (Burla et al., 2005); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and PLATON (Spek, 2009).

Figures

	Fig. 1. The molecular structure of (I), showing the atom-labelling scheme and the intramolecular N—H···O hydrogen bond (dashed line). Displacement ellipsoids are drawn at the 50% probability level.
	Fig. 2. Part of the crystal structure of (I), showing the formation of a cyclic centrosymmetric dimer built from paired C—H···O hydrogen bonds. For the sake of clarity, H atoms bonded to C atoms but not involved in the motif shown have been omitted. Atoms marked with an asterisk (*) are at the symmetry position (1 - x, 2 - y, 1 - z).
	Fig. 3. A stereoview of part of the crystal structure of (I), showing the formation of a hydrogen-bonded sheet parallel to (101) and containing N—H···O, N—H···N and C—H···O hydrogen bonds. For the sake of clarity, H atoms bonded to C atoms but not involved in the motifs shown have been omitted.
	Fig. 4. Part of the crystal structure of (I), showing the formation of a cyclic dimer built from paired C—H···π(arene hydrogen bonds. For the sake of clarity, H atoms not involved in the motif shown have been omitted. The atom marked with a hash (#) is at the symmetry position (1 - x, y, 1/2 - z).

1-(2-Aminophenyl)-3-(4-pyridyl)prop-2-en-1-one

Crystal data

C14H12N2O	F(000) = 944
Mr = 224.26	Dx = 1.292 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 2653 reflections
a = 27.922 (6) Å	θ = 3.2–27.5°
b = 6.4261 (8) Å	µ = 0.08 mm^−1
c = 14.668 (3) Å	T = 296 K
β = 118.849 (18)°	Block, orange
V = 2305.2 (8) Å^3	0.30 × 0.17 × 0.16 mm
Z = 8

Data collection

Bruker Nonius KappaCCD area-detector diffractometer	2141 independent reflections
Radiation source: Bruker Nonius FR591 rotating anode	1403 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.036
Detector resolution: 9.091 pixels mm^-1	θmax = 25.5°, θmin = 3.2°
ϕ and ω scans	h = −33→33
Absorption correction: multi-scan (SADABS; Version 2.10, Sheldrick, 2003)	k = −7→7
Tmin = 0.954, Tmax = 0.987	l = −17→17
17566 measured reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.049	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.126	H-atom parameters constrained
S = 1.08	w = 1/[σ^2(Fo^2) + (0.0458P)^2 + 1.0151P] where P = (Fo^2 + 2Fc^2)/3
2141 reflections	(Δ/σ)max = 0.001
154 parameters	Δρmax = 0.13 e Å^−3
0 restraints	Δρmin = −0.15 e Å^−3

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
C1	0.54321 (7)	0.5981 (3)	0.44396 (15)	0.0621 (5)
O1	0.56037 (5)	0.7445 (2)	0.50476 (12)	0.0842 (5)
C2	0.48413 (7)	0.5926 (3)	0.37024 (14)	0.0649 (5)
H2	0.4698	0.4822	0.3237	0.078*
C3	0.45158 (7)	0.7384 (3)	0.36882 (14)	0.0626 (5)
H3	0.4680	0.8470	0.4157	0.075*
C11	0.57932 (7)	0.4371 (3)	0.44259 (14)	0.0608 (5)
C12	0.63656 (7)	0.4588 (3)	0.50055 (15)	0.0667 (5)
C13	0.66903 (9)	0.2986 (4)	0.49596 (18)	0.0840 (7)
H13	0.7069	0.3115	0.5333	0.101*
C14	0.64724 (12)	0.1269 (5)	0.4393 (2)	0.0985 (8)
H14	0.6701	0.0231	0.4379	0.118*
C15	0.59151 (12)	0.1022 (4)	0.3834 (2)	0.0953 (7)
H15	0.5766	−0.0175	0.3442	0.114*
C16	0.55856 (9)	0.2545 (3)	0.38591 (16)	0.0745 (6)
H16	0.5209	0.2365	0.3486	0.089*
N12	0.66033 (6)	0.6265 (3)	0.55805 (15)	0.0893 (6)
H12A	0.6387	0.7218	0.5616	0.107*
H12B	0.6961	0.6417	0.5923	0.107*
C31	0.39277 (7)	0.7529 (3)	0.30313 (13)	0.0601 (5)
C32	0.36174 (7)	0.6042 (4)	0.23288 (16)	0.0791 (6)
H32	0.3779	0.4843	0.2247	0.095*
C33	0.30680 (9)	0.6335 (4)	0.17490 (19)	0.0964 (8)
H33	0.2866	0.5308	0.1271	0.116*
N34	0.28030 (7)	0.7964 (4)	0.18169 (15)	0.0911 (6)
C35	0.31025 (8)	0.9374 (4)	0.24939 (18)	0.0933 (8)
H35	0.2928	1.0543	0.2568	0.112*
C36	0.36590 (7)	0.9231 (4)	0.31018 (16)	0.0819 (7)
H36	0.3852	1.0299	0.3562	0.098*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0487 (10)	0.0718 (13)	0.0622 (11)	−0.0057 (9)	0.0238 (8)	−0.0036 (10)
O1	0.0475 (7)	0.0860 (10)	0.0983 (10)	−0.0022 (7)	0.0187 (7)	−0.0259 (9)
C2	0.0499 (10)	0.0798 (13)	0.0627 (11)	−0.0073 (10)	0.0254 (8)	−0.0109 (10)
C3	0.0458 (9)	0.0781 (13)	0.0578 (10)	−0.0061 (10)	0.0201 (8)	−0.0066 (10)
C11	0.0588 (10)	0.0681 (13)	0.0591 (10)	0.0050 (10)	0.0312 (9)	0.0064 (10)
C12	0.0553 (11)	0.0820 (14)	0.0621 (11)	0.0107 (11)	0.0278 (9)	0.0155 (11)
C13	0.0731 (13)	0.0977 (18)	0.0880 (15)	0.0285 (14)	0.0443 (12)	0.0261 (14)
C14	0.109 (2)	0.094 (2)	0.1089 (19)	0.0396 (17)	0.0653 (17)	0.0243 (16)
C15	0.120 (2)	0.0780 (16)	0.1002 (17)	0.0125 (15)	0.0632 (16)	−0.0031 (14)
C16	0.0787 (13)	0.0767 (14)	0.0731 (13)	0.0018 (12)	0.0405 (11)	0.0013 (12)
N12	0.0437 (8)	0.1031 (15)	0.1013 (14)	0.0064 (9)	0.0194 (9)	−0.0078 (12)
C31	0.0452 (9)	0.0824 (13)	0.0535 (10)	−0.0035 (9)	0.0245 (8)	−0.0057 (10)
C32	0.0491 (11)	0.0922 (16)	0.0841 (14)	−0.0083 (11)	0.0228 (10)	−0.0216 (12)
C33	0.0537 (12)	0.118 (2)	0.1001 (17)	−0.0159 (13)	0.0231 (12)	−0.0340 (15)
N34	0.0454 (9)	0.1304 (17)	0.0867 (13)	−0.0041 (11)	0.0232 (9)	−0.0191 (13)
C35	0.0561 (12)	0.124 (2)	0.0931 (16)	0.0118 (13)	0.0305 (12)	−0.0241 (16)
C36	0.0516 (11)	0.1071 (18)	0.0746 (13)	0.0018 (11)	0.0207 (10)	−0.0252 (13)

Geometric parameters (Å, º)

C11—C12	1.409 (3)	C14—H14	0.9300
C12—C13	1.395 (3)	C15—H15	0.9300
C13—C14	1.338 (3)	C16—H16	0.9300
C14—C15	1.374 (3)	N12—H12A	0.8799
C15—C16	1.356 (3)	N12—H12B	0.8801
C16—C11	1.392 (3)	C31—C36	1.358 (3)
C12—N12	1.331 (3)	C31—C32	1.365 (3)
C1—C11	1.452 (3)	C32—C33	1.361 (3)
C1—O1	1.224 (2)	C32—H32	0.9300
C1—C2	1.473 (2)	C33—N34	1.313 (3)
C2—C3	1.299 (2)	C33—H33	0.9300
C2—H2	0.9300	N34—C35	1.306 (3)
C3—C31	1.451 (2)	C35—C36	1.371 (3)
C3—H3	0.9300	C35—H35	0.9300
C13—H13	0.9300	C36—H36	0.9300
O1—C1—C11	121.84 (16)	C14—C15—H15	120.4
O1—C1—C2	117.37 (17)	C15—C16—C11	122.1 (2)
C11—C1—C2	120.78 (18)	C15—C16—H16	118.9
C3—C2—C1	121.42 (18)	C11—C16—H16	118.9
C3—C2—H2	119.3	C12—N12—H12A	117.0
C1—C2—H2	119.3	C12—N12—H12B	122.2
C2—C3—C31	128.00 (18)	H12A—N12—H12B	120.8
C2—C3—H3	116.0	C36—C31—C32	116.65 (17)
C31—C3—H3	116.0	C36—C31—C3	119.38 (18)
C16—C11—C12	117.90 (19)	C32—C31—C3	123.97 (18)
C16—C11—C1	121.14 (17)	C33—C32—C31	119.2 (2)
C12—C11—C1	120.95 (18)	C33—C32—H32	120.4
N12—C12—C13	119.41 (19)	C31—C32—H32	120.4
N12—C12—C11	122.41 (18)	N34—C33—C32	124.7 (2)
C13—C12—C11	118.2 (2)	N34—C33—H33	117.6
C14—C13—C12	121.8 (2)	C32—C33—H33	117.6
C14—C13—H13	119.1	C35—N34—C33	115.67 (18)
C12—C13—H13	119.1	N34—C35—C36	123.9 (2)
C13—C14—C15	120.7 (2)	N34—C35—H35	118.1
C13—C14—H14	119.6	C36—C35—H35	118.1
C15—C14—H14	119.6	C31—C36—C35	119.9 (2)
C16—C15—C14	119.2 (2)	C31—C36—H36	120.1
C16—C15—H15	120.4	C35—C36—H36	120.1
C12—C11—C1—C2	169.49 (17)	C13—C14—C15—C16	0.1 (4)
C11—C1—C2—C3	−178.21 (18)	C14—C15—C16—C11	0.8 (3)
O1—C1—C2—C3	0.8 (3)	C12—C11—C16—C15	−1.5 (3)
C1—C2—C3—C31	−178.49 (18)	C1—C11—C16—C15	179.88 (19)
O1—C1—C11—C16	169.07 (18)	C2—C3—C31—C36	−177.3 (2)
C2—C1—C11—C16	−11.9 (3)	C2—C3—C31—C32	2.6 (3)
O1—C1—C11—C12	−9.5 (3)	C36—C31—C32—C33	0.0 (3)
C16—C11—C12—N12	−179.29 (19)	C3—C31—C32—C33	−179.9 (2)
C1—C11—C12—N12	−0.7 (3)	C31—C32—C33—N34	−0.7 (4)
C16—C11—C12—C13	1.4 (3)	C32—C33—N34—C35	0.3 (4)
C1—C11—C12—C13	−179.99 (18)	C33—N34—C35—C36	0.6 (4)
N12—C12—C13—C14	−180.0 (2)	C32—C31—C36—C35	0.9 (3)
C11—C12—C13—C14	−0.6 (3)	C3—C31—C36—C35	−179.2 (2)
C12—C13—C14—C15	−0.1 (4)	N34—C35—C36—C31	−1.3 (4)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N12—H12A···O1	0.88	1.93	2.621 (3)	134
N12—H12B···N34^i	0.88	2.10	2.982 (3)	174
C36—H36···O1^ii	0.93	2.36	3.283 (3)	170
C32—H32···Cg1^iii	0.93	2.87	3.611 (3)	137

Symmetry codes: (i) x+1/2, −y+3/2, z+1/2; (ii) −x+1, −y+2, −z+1; (iii) −x+1, y, −z+1/2.