organic compounds
2-Cyano-5-({4-[N-methyl-N-(2-hydroxyethyl)amino] phenyl}diazenyl)pyridine
aDipartimento di Scienze Chimiche, Università degli Studi di Napoli 'Federico II', Complesso di Monte S. Angelo, Via Cinthia, 80126 Napoli, Italy
*Correspondence e-mail: roberto.centore@unina.it
In the title compound, C15H15N5O, the benzene and pyridine rings make a dihedral angle of 30.86 (7)°. In the crystal, chains of molecules are wrapped around the screw axes into compressed helices, through hydrogen bonding between the hydroxy and cyano groups. The chains are linked by weak C—H⋯N and C—H⋯O interactions. The π conjugated unit of the molecule is almost perpendicular to the helix axis, and the formation of the helix is allowed by a gauche-type torsion angle in the hydroxyethyl tail. In this way, consecutive chromophore units along the chain are placed in a strict antiparallel arrangement, and this is energetically favoured because of the high of the molecule.
Related literature
For general information on non-linear optical compounds, see: Singer et al. (1989); Dalton (2002). For structural and theoretical analysis of conjugation in push–pull molecules, see: Gainsford et al. (2008); Centore et al. (2009); Capobianco et al. (2012). For the local packing modes of non-linear optical chromophores, see: Coe et al. (2000); Thallapally et al. (2002); Centore et al. (2006). For theoretical computations on similar compounds, see: Willets et al. (1992); Castaldo et al. (2002); Locatelli et al. (2005). For the CSD see: Allen (2002). For the synthesis of related compounds, see: Bruno et al. (2002); Centore et al. (2007); Centore et al. (2012).
Experimental
Crystal data
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Refinement
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Data collection: COLLECT (Nonius, 1999); cell CELLFITW (Centore, 2004); data reduction: EVALCCD (Duisenberg et al., 2003); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and Mercury (Macrae et al., 2006); software used to prepare material for publication: WinGX (Farrugia, 2012).
Supporting information
10.1107/S1600536812041396/fj2599sup1.cif
contains datablocks global, I. DOI:Structure factors: contains datablock I. DOI: 10.1107/S1600536812041396/fj2599Isup2.hkl
Supporting information file. DOI: 10.1107/S1600536812041396/fj2599Isup3.cml
(I) was prepared by diazotization of 5-amino-2-cyanopyridine followed by coupling with N-methyl-N-(2-hydroxyethyl)aniline. The procedure of diazo-coupling is analogous to that we have already described for the synthesis of similar diazo-chromophores (Bruno et al., 2002; Centore et al., 2007; Centore et al., 2012). Purification of (I) was obtained by recrystallization from ethanol. The final yield for the diazotization/coupling step was 69%. Mp. 166 °C. Single crystals were obtained by slow evaporation from ethanol solutions. 1H-NMR (py-d5) δ 3.06 (3, 3H), 3.71 (t, 2H), 4.00 (t, 2H), 4.80 (s, 1H), 6.92 (d, 2H, J = 11 Hz), 7.84–8.19 (m, 4H), 9.26 (d, 1H, J = 2.6 Hz). Electro-optical absorption spectroscopy data of (I) (dioxane solution; quadratic hyperpolarizability is given according to the phenomenological convention (X convention) (Willets et al., 1992)): λmax = 461.3 nm, µg = 8.16 D, Δµ = 12.5 D, β0 = 69×10-30 esu, µgβ0 = 566×10-48 esu.
The H atom of the hydroxy group was located in difmap. All other H atoms were generated stereochemically. All H atoms were refined by the riding model with Uiso=1.2×Ueq of the
(1.5 for H atoms of the methyl group).Data collection: COLLECT (Nonius, 1999); cell
CELLFITW (Centore, 2004); data reduction: EVALCCD (Duisenberg et al., 2003); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and Mercury (Macrae et al., 2006); software used to prepare material for publication: WinGX (Farrugia, 2012).Fig. 1. ORTEP view of the molecular structure of (I). Thermal ellipsoids are drawn at 30% probability level. | |
Fig. 2. Row of H-bonded molecules of (I). | |
Fig. 3. Lateral packing of (I) along b. |
C15H15N5O | Dx = 1.341 Mg m−3 |
Mr = 281.32 | Melting point: 439 K |
Monoclinic, P21/c | Mo Kα radiation, λ = 0.71073 Å |
a = 17.755 (8) Å | Cell parameters from 76 reflections |
b = 7.240 (4) Å | θ = 5.6–23.2° |
c = 11.045 (8) Å | µ = 0.09 mm−1 |
β = 101.07 (5)° | T = 293 K |
V = 1393.4 (14) Å3 | Plate, red |
Z = 4 | 0.40 × 0.10 × 0.05 mm |
F(000) = 592 |
Bruker–Nonius KappaCCD diffractometer | 2403 independent reflections |
Radiation source: fine-focus sealed tube | 1336 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.069 |
Detector resolution: 9 pixels mm-1 | θmax = 25.0°, θmin = 3.1° |
CCD rotation images, thick slices scans | h = −20→21 |
Absorption correction: multi-scan (SADABS; Bruker, 2001) | k = −7→8 |
Tmin = 0.965, Tmax = 0.996 | l = −13→11 |
8528 measured reflections |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.052 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.139 | H-atom parameters constrained |
S = 1.02 | w = 1/[σ2(Fo2) + (0.0646P)2 + 0.0464P] where P = (Fo2 + 2Fc2)/3 |
2403 reflections | (Δ/σ)max < 0.001 |
191 parameters | Δρmax = 0.14 e Å−3 |
0 restraints | Δρmin = −0.21 e Å−3 |
C15H15N5O | V = 1393.4 (14) Å3 |
Mr = 281.32 | Z = 4 |
Monoclinic, P21/c | Mo Kα radiation |
a = 17.755 (8) Å | µ = 0.09 mm−1 |
b = 7.240 (4) Å | T = 293 K |
c = 11.045 (8) Å | 0.40 × 0.10 × 0.05 mm |
β = 101.07 (5)° |
Bruker–Nonius KappaCCD diffractometer | 2403 independent reflections |
Absorption correction: multi-scan (SADABS; Bruker, 2001) | 1336 reflections with I > 2σ(I) |
Tmin = 0.965, Tmax = 0.996 | Rint = 0.069 |
8528 measured reflections |
R[F2 > 2σ(F2)] = 0.052 | 0 restraints |
wR(F2) = 0.139 | H-atom parameters constrained |
S = 1.02 | Δρmax = 0.14 e Å−3 |
2403 reflections | Δρmin = −0.21 e Å−3 |
191 parameters |
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. |
Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger. |
x | y | z | Uiso*/Ueq | ||
C1 | 0.39381 (17) | 0.5114 (4) | −0.0089 (3) | 0.0658 (9) | |
H1A | 0.4101 | 0.4652 | −0.0821 | 0.079* | |
H1B | 0.3398 | 0.5431 | −0.0314 | 0.079* | |
C2 | 0.40363 (16) | 0.3604 (3) | 0.0877 (3) | 0.0539 (7) | |
H2A | 0.3763 | 0.2511 | 0.0523 | 0.065* | |
H2B | 0.4576 | 0.3290 | 0.1102 | 0.065* | |
C3 | 0.43153 (16) | 0.4817 (4) | 0.3024 (3) | 0.0634 (8) | |
H3A | 0.4355 | 0.3973 | 0.3704 | 0.095* | |
H3B | 0.4154 | 0.6004 | 0.3266 | 0.095* | |
H3C | 0.4806 | 0.4931 | 0.2788 | 0.095* | |
C4 | 0.29960 (14) | 0.4002 (3) | 0.2038 (2) | 0.0389 (6) | |
C5 | 0.27273 (14) | 0.4488 (3) | 0.3117 (2) | 0.0426 (7) | |
H5 | 0.3073 | 0.4906 | 0.3803 | 0.051* | |
C6 | 0.19600 (15) | 0.4353 (3) | 0.3169 (2) | 0.0416 (6) | |
H6 | 0.1799 | 0.4664 | 0.3895 | 0.050* | |
C7 | 0.14206 (14) | 0.3759 (3) | 0.2154 (2) | 0.0356 (6) | |
C8 | 0.16750 (14) | 0.3312 (3) | 0.1079 (2) | 0.0412 (6) | |
H8 | 0.1322 | 0.2941 | 0.0388 | 0.049* | |
C9 | 0.24378 (14) | 0.3407 (3) | 0.1019 (2) | 0.0423 (7) | |
H9 | 0.2593 | 0.3072 | 0.0292 | 0.051* | |
C10 | −0.03818 (14) | 0.3687 (3) | 0.3055 (2) | 0.0377 (6) | |
C11 | −0.09206 (15) | 0.4028 (3) | 0.2005 (2) | 0.0445 (7) | |
H11 | −0.0770 | 0.4255 | 0.1258 | 0.053* | |
C12 | −0.16836 (15) | 0.4026 (3) | 0.2081 (2) | 0.0479 (7) | |
H12 | −0.2061 | 0.4250 | 0.1387 | 0.058* | |
C13 | −0.18771 (15) | 0.3687 (3) | 0.3206 (3) | 0.0420 (6) | |
C14 | −0.06318 (15) | 0.3353 (3) | 0.4146 (2) | 0.0484 (7) | |
H14 | −0.0264 | 0.3124 | 0.4852 | 0.058* | |
C15 | −0.26695 (18) | 0.3730 (3) | 0.3352 (3) | 0.0519 (7) | |
N1 | 0.37562 (12) | 0.4124 (3) | 0.1987 (2) | 0.0459 (6) | |
N2 | 0.06251 (12) | 0.3612 (2) | 0.21080 (19) | 0.0417 (5) | |
N3 | 0.04319 (12) | 0.3723 (3) | 0.3147 (2) | 0.0455 (6) | |
N4 | −0.13639 (13) | 0.3339 (3) | 0.4246 (2) | 0.0493 (6) | |
N5 | −0.32935 (16) | 0.3783 (3) | 0.3473 (3) | 0.0743 (8) | |
O1 | 0.43618 (12) | 0.6724 (3) | 0.0323 (2) | 0.0771 (7) | |
H1O | 0.4068 | 0.7588 | 0.0816 | 0.093* |
U11 | U22 | U33 | U12 | U13 | U23 | |
C1 | 0.0473 (19) | 0.093 (2) | 0.063 (2) | 0.0003 (17) | 0.0247 (16) | 0.0034 (17) |
C2 | 0.0400 (17) | 0.0608 (17) | 0.067 (2) | 0.0028 (13) | 0.0272 (15) | −0.0057 (14) |
C3 | 0.0399 (18) | 0.086 (2) | 0.064 (2) | −0.0063 (15) | 0.0079 (16) | 0.0043 (16) |
C4 | 0.0361 (17) | 0.0363 (14) | 0.0476 (17) | 0.0008 (11) | 0.0161 (13) | 0.0059 (11) |
C5 | 0.0417 (17) | 0.0504 (15) | 0.0365 (16) | −0.0018 (11) | 0.0096 (13) | 0.0015 (11) |
C6 | 0.0458 (18) | 0.0425 (14) | 0.0411 (16) | 0.0033 (11) | 0.0202 (14) | 0.0034 (11) |
C7 | 0.0308 (15) | 0.0362 (13) | 0.0420 (16) | −0.0004 (10) | 0.0128 (13) | 0.0053 (11) |
C8 | 0.0390 (17) | 0.0465 (15) | 0.0391 (16) | −0.0018 (11) | 0.0102 (13) | −0.0007 (11) |
C9 | 0.0440 (18) | 0.0458 (15) | 0.0411 (17) | −0.0047 (12) | 0.0186 (13) | −0.0054 (11) |
C10 | 0.0328 (16) | 0.0368 (14) | 0.0464 (17) | −0.0024 (10) | 0.0152 (13) | −0.0026 (11) |
C11 | 0.0447 (18) | 0.0501 (15) | 0.0432 (17) | −0.0018 (12) | 0.0195 (14) | −0.0005 (11) |
C12 | 0.0415 (19) | 0.0572 (17) | 0.0463 (18) | 0.0016 (12) | 0.0113 (14) | 0.0006 (12) |
C13 | 0.0404 (17) | 0.0366 (14) | 0.0537 (18) | −0.0061 (11) | 0.0207 (15) | −0.0089 (12) |
C14 | 0.0409 (19) | 0.0608 (17) | 0.0449 (18) | −0.0036 (13) | 0.0117 (14) | 0.0022 (12) |
C15 | 0.049 (2) | 0.0473 (16) | 0.064 (2) | −0.0056 (13) | 0.0236 (16) | −0.0076 (13) |
N1 | 0.0332 (14) | 0.0546 (13) | 0.0525 (15) | 0.0002 (10) | 0.0153 (11) | −0.0010 (10) |
N2 | 0.0466 (16) | 0.0383 (12) | 0.0435 (14) | 0.0014 (9) | 0.0174 (11) | 0.0022 (9) |
N3 | 0.0462 (16) | 0.0468 (12) | 0.0469 (14) | −0.0011 (10) | 0.0180 (11) | 0.0027 (10) |
N4 | 0.0442 (16) | 0.0613 (14) | 0.0461 (15) | −0.0063 (11) | 0.0183 (12) | −0.0022 (10) |
N5 | 0.0514 (19) | 0.0733 (17) | 0.108 (2) | −0.0089 (13) | 0.0397 (16) | −0.0089 (15) |
O1 | 0.0668 (16) | 0.0722 (14) | 0.1043 (18) | −0.0004 (11) | 0.0466 (13) | 0.0101 (12) |
C1—O1 | 1.414 (3) | C7—N2 | 1.408 (3) |
C1—C2 | 1.514 (4) | C8—C9 | 1.370 (3) |
C1—H1A | 0.9700 | C8—H8 | 0.9300 |
C1—H1B | 0.9700 | C9—H9 | 0.9300 |
C2—N1 | 1.458 (3) | C10—C11 | 1.376 (4) |
C2—H2A | 0.9700 | C10—C14 | 1.383 (3) |
C2—H2B | 0.9700 | C10—N3 | 1.429 (3) |
C3—N1 | 1.454 (3) | C11—C12 | 1.373 (3) |
C3—H3A | 0.9600 | C11—H11 | 0.9300 |
C3—H3B | 0.9600 | C12—C13 | 1.373 (3) |
C3—H3C | 0.9600 | C12—H12 | 0.9300 |
C4—N1 | 1.365 (3) | C13—N4 | 1.346 (3) |
C4—C5 | 1.410 (3) | C13—C15 | 1.447 (4) |
C4—C9 | 1.416 (3) | C14—N4 | 1.325 (3) |
C5—C6 | 1.378 (3) | C14—H14 | 0.9300 |
C5—H5 | 0.9300 | C15—N5 | 1.142 (3) |
C6—C7 | 1.395 (3) | N2—N3 | 1.262 (3) |
C6—H6 | 0.9300 | O1—H1O | 1.0341 |
C7—C8 | 1.387 (3) | ||
O1—C1—C2 | 112.8 (2) | C9—C8—C7 | 121.1 (2) |
O1—C1—H1A | 109.0 | C9—C8—H8 | 119.4 |
C2—C1—H1A | 109.0 | C7—C8—H8 | 119.4 |
O1—C1—H1B | 109.0 | C8—C9—C4 | 121.6 (2) |
C2—C1—H1B | 109.0 | C8—C9—H9 | 119.2 |
H1A—C1—H1B | 107.8 | C4—C9—H9 | 119.2 |
N1—C2—C1 | 113.2 (2) | C11—C10—C14 | 118.5 (2) |
N1—C2—H2A | 108.9 | C11—C10—N3 | 125.9 (2) |
C1—C2—H2A | 108.9 | C14—C10—N3 | 115.5 (2) |
N1—C2—H2B | 108.9 | C12—C11—C10 | 118.9 (3) |
C1—C2—H2B | 108.9 | C12—C11—H11 | 120.6 |
H2A—C2—H2B | 107.8 | C10—C11—H11 | 120.6 |
N1—C3—H3A | 109.5 | C13—C12—C11 | 118.5 (3) |
N1—C3—H3B | 109.5 | C13—C12—H12 | 120.8 |
H3A—C3—H3B | 109.5 | C11—C12—H12 | 120.8 |
N1—C3—H3C | 109.5 | N4—C13—C12 | 124.0 (3) |
H3A—C3—H3C | 109.5 | N4—C13—C15 | 115.0 (2) |
H3B—C3—H3C | 109.5 | C12—C13—C15 | 121.0 (3) |
N1—C4—C5 | 121.1 (2) | N4—C14—C10 | 123.9 (3) |
N1—C4—C9 | 122.2 (2) | N4—C14—H14 | 118.1 |
C5—C4—C9 | 116.6 (2) | C10—C14—H14 | 118.1 |
C6—C5—C4 | 121.0 (2) | N5—C15—C13 | 179.3 (3) |
C6—C5—H5 | 119.5 | C4—N1—C3 | 121.4 (2) |
C4—C5—H5 | 119.5 | C4—N1—C2 | 121.2 (2) |
C5—C6—C7 | 121.3 (2) | C3—N1—C2 | 117.4 (2) |
C5—C6—H6 | 119.3 | N3—N2—C7 | 114.1 (2) |
C7—C6—H6 | 119.3 | N2—N3—C10 | 112.4 (2) |
C8—C7—C6 | 118.3 (2) | C14—N4—C13 | 116.2 (2) |
C8—C7—N2 | 116.1 (2) | C1—O1—H1O | 112.1 |
C6—C7—N2 | 125.6 (2) | ||
O1—C1—C2—N1 | 62.7 (3) | C11—C10—C14—N4 | 0.0 (3) |
N1—C4—C5—C6 | −179.6 (2) | N3—C10—C14—N4 | 177.4 (2) |
C9—C4—C5—C6 | 1.1 (3) | C5—C4—N1—C3 | −2.1 (3) |
C4—C5—C6—C7 | −1.0 (3) | C9—C4—N1—C3 | 177.2 (2) |
C5—C6—C7—C8 | −0.3 (3) | C5—C4—N1—C2 | 179.4 (2) |
C5—C6—C7—N2 | −178.6 (2) | C9—C4—N1—C2 | −1.4 (3) |
C6—C7—C8—C9 | 1.5 (3) | C1—C2—N1—C4 | 82.0 (3) |
N2—C7—C8—C9 | 180.0 (2) | C1—C2—N1—C3 | −96.6 (3) |
C7—C8—C9—C4 | −1.4 (3) | C8—C7—N2—N3 | 168.65 (18) |
N1—C4—C9—C8 | −179.2 (2) | C6—C7—N2—N3 | −13.0 (3) |
C5—C4—C9—C8 | 0.1 (3) | C7—N2—N3—C10 | 176.23 (17) |
C14—C10—C11—C12 | 0.1 (3) | C11—C10—N3—N2 | −18.0 (3) |
N3—C10—C11—C12 | −176.9 (2) | C14—C10—N3—N2 | 164.91 (19) |
C10—C11—C12—C13 | 0.1 (3) | C10—C14—N4—C13 | −0.4 (3) |
C11—C12—C13—N4 | −0.6 (4) | C12—C13—N4—C14 | 0.7 (3) |
C11—C12—C13—C15 | 177.8 (2) | C15—C13—N4—C14 | −177.8 (2) |
D—H···A | D—H | H···A | D···A | D—H···A |
O1—H1O···N5i | 1.03 | 1.92 | 2.925 (4) | 165 |
C6—H6···N4ii | 0.93 | 2.74 | 3.637 (4) | 162 |
C2—H2B···O1iii | 0.97 | 2.68 | 3.369 (4) | 129 |
Symmetry codes: (i) −x, y+1/2, −z+1/2; (ii) −x, −y+1, −z+1; (iii) −x+1, −y+1, −z. |
Experimental details
Crystal data | |
Chemical formula | C15H15N5O |
Mr | 281.32 |
Crystal system, space group | Monoclinic, P21/c |
Temperature (K) | 293 |
a, b, c (Å) | 17.755 (8), 7.240 (4), 11.045 (8) |
β (°) | 101.07 (5) |
V (Å3) | 1393.4 (14) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.09 |
Crystal size (mm) | 0.40 × 0.10 × 0.05 |
Data collection | |
Diffractometer | Bruker–Nonius KappaCCD diffractometer |
Absorption correction | Multi-scan (SADABS; Bruker, 2001) |
Tmin, Tmax | 0.965, 0.996 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 8528, 2403, 1336 |
Rint | 0.069 |
(sin θ/λ)max (Å−1) | 0.595 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.052, 0.139, 1.02 |
No. of reflections | 2403 |
No. of parameters | 191 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.14, −0.21 |
Computer programs: COLLECT (Nonius, 1999), CELLFITW (Centore, 2004), EVALCCD (Duisenberg et al., 2003), SIR97 (Altomare et al., 1999), SHELXL97 (Sheldrick, 2008), ORTEP-3 for Windows (Farrugia, 2012) and Mercury (Macrae et al., 2006), WinGX (Farrugia, 2012).
D—H···A | D—H | H···A | D···A | D—H···A |
O1—H1O···N5i | 1.03 | 1.92 | 2.925 (4) | 165 |
C6—H6···N4ii | 0.93 | 2.74 | 3.637 (4) | 162 |
C2—H2B···O1iii | 0.97 | 2.68 | 3.369 (4) | 129 |
Symmetry codes: (i) −x, y+1/2, −z+1/2; (ii) −x, −y+1, −z+1; (iii) −x+1, −y+1, −z. |
Acknowledgements
The authors thank the Centro Interdipartimentale di Metodologie Chimico–Fisiche, Università degli Studi di Napoli "Federico II". Thanks are also due to Professor H.-G. Kuball for the spectroscopic measurements.
References
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This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.
Organic nonlinear optical (NLO) chromophores are currently under investigation because of possible applications in optical data processing (Dalton, 2002). The chemical investigation is mainly directed to the synthesis of chromophores of increasing quadratic nonlinear optical activity. However, also the structural investigation of NLO chromophores is relevant, pointing towards the quantitative evaluation of the structural parameters related to the conjugation in push-pull molecules (Gainsford et al., 2008; Capobianco et al., 2012) and to the rationalization of the local packing modes of chromophore units (Coe et al., 2000; Thallapally et al., 2002; Centore et al., 2006).
Compound (I), 2-cyano-5-[4-(N-methyl-N-(2-hydroxyethyl)amino)- 1-diazenylphenyl]pyridine, is a typical push-pull azo-dye, containing the dialkylamino as donor group and the cyano as acceptor. Moreover, the cyano group is attached to an electron poor pyridine ring, and this should increase the electron withdrawing character. This compound has been used in the synthesis of cross-linked systems showing both piezoelectric and quadratic NLO behaviour (Centore et al., 2012).
The molecular structure of (I) is shown in Fig. 1. The geometry around the donor N1 atom is substantially planar indicating sp2 hybridization (the sum of valence angles at N1 is 360°) and the pattern of bond lenghts within the adjacent phenyl ring shows a certain degree of quinoidal character. All these structural features are in accordance with the expected π conjugation and push-pull character of the chromophore group.
The two aromatic rings are not coplanar, the dihedral angle between the mean planes being 30.86 (7)°; this twist, which is mainly due to a torsion around the bond N3—C10, is not expected to negatively affect the quadratic NLO performances of the molecule, as it has been proved both theoretically and experimentally for similar chromophores (Castaldo et al., 2002; Locatelli et al., 2005).
Nonlinear optical properties of (I) have been determined by means of electro-optical absorption spectroscopy measurements in dioxane solution (Centore et al., 2009). Relevant data are given in the Experimental part. We note that the dipole moment of the ground state is rather high and also the change in dipole moment between the ground and the first excited state is high, coherently with the expected charge-transfer character of the HOMO-LUMO transition. The quadratic NLO activity of (I), measured by the µβ0 product, is also significant, if we consider the simple chemical structure of the compound, and is comparable with the NLO reference compound DANS (Singer et al., 1989).
Molecules in the crystal form rows through hydrogen bonds between hydroxy and cyano groups of consecutive molecules, Fig. 2 and Table 1. The chains, which have graph set symbol C11(17), are wrapped around crystallographic binary screw axes. Actually, the pitch of the helix (b=7.240 (4) Å) is very short, as compared with the length of the molecule (N5···O1= 14.818 (8) Å), so the helix is very compressed; in fact, the π conjugated unit of the molecule is almost perpendicular to the helix axis, and the formation of the helix is is allowed by a gauche-type torsion angle in the hydroxyethyl tail. In this way, consecutive chromophore units along the chain are placed in a strict antiparallel arrangement, and this is energetically favoured because of the high dipole moment of the molecule.
Along (b+c) and a+b directions, the chains are held by weaker interactions involving C—H aromatic donor and pyridine N acceptor groups or C—H aliphatic donor and O acceptor groups (Fig. 3 and Table 1). Two dimeric ring patterns can be recognized, having graph set symbols R22(16) and R22(8); both are formed across crystallographic inversion centers.
A search within CSD (version 5.33) (Allen, 2002) has shown that these patterns are unprecedented in compounds containing N-methyl-N-2- hydroxyethylamino and azopyridyl-benzene mojeties.