Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S010827010100909X/bm1452sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S010827010100909X/bm1452Isup2.hkl | |
Structure factor file (CIF format) https://doi.org/10.1107/S010827010100909X/bm1452IIsup3.hkl |
CCDC references: 170216; 170217
Compound (1) was synthesized by the Knoevenagel condensation method. A clear solution of N-methyl cyanoacetamide (0.98 g, 0.01 mol) and phenylpropiolic aldehyde (1.44 g, 0.01 mol) in N-methylpyrrolidone (NMP, 3 ml) was stirred with aluminium oxide (5 g) as catalyst until the exothermic reaction had ceased and the reaction mixture had solidified. AUTHOR: Please check the wording above. After being left to stand overnight at room temperature, further NMP (5 ml) was added. The precipitate was filtered off and washed with NMP (5 ml). AUTHOR: It is not clear what is happening below. Does the following procedure result in more of the same material? The filtrate was poured into water and the precipitate was separated and crystallized from toluene (yield 67%). Spectroscopic analysis: 1H NMR (400.26 MHz, acetone, δ, p.p.m): 2.90 (d, J = 4.8 Hz, 3H, CH3), 7.47–7.62 (m, 7H, CH + NH + 5Harom). Crystals of the polymorphic forms (I) and (II) were obtained by isothermal evaporation from CCl4 and n-C6H14 solutions, respectively. The melting point of (I) is 381 K and the melting point of (II) is 384 K. IR spectra were recorded on a Perkin-Elmer 1725 F T—IR spectrometer with a modified sample holder (Shchegolikhin & Lazareva, 1997). Optimization of the crystal structures of (I) and (II) and calculation of the lattice energies were carried out using Cerius2 (Molecular Simulations, 1999), taking into account their monoclinic cell setting (i.e. the angles α and γ were constrained) using the `Smart Minimizer' option of the Cerius2 package. Using this option, optimization begins with a steepest descent method, followed by a quasi-Newton method and finishing with a truncated Newton method. Atom-atom potentials were estimated using the Dreiding 2.21 forcefield (Mayo et al., 1990) and atomic charges were estimated using the charge equilibration method (Rappé & Goddard, 1991). All molecules in the crystal were treated as rigid entities. In this case, the total lattice energy is the sum of three contributions, namely van der Waals, Coulombic and hydrogen-bonding.
For polymorph (I), all H atoms were refined freely. For polymorph (II), H atoms were treated as riding, with C—H = 0.93–0.96 Å, N—H = 0.86 Å and Uiso(H) = 1.2Ueq of the parent atom. Query.
Derivatives of 2-cyanoacrylic acid with unsaturated substitutents in the 3-position are of great interest because of their potential bioactivity and versatility in the synthesis of polymeric and heterocyxlic compounds. For example, such compounds can undergo polymerization under very mild conditions (Gololobov & Gruber, 1997; Denchev & Kabaivanov, 1993). In addition, our previous structural studies show that topochemical reactions can occur in some of these derivatives, namely in 2-cyano-(2E)-pentadien-2,4-oic acid and its ethyl ester (Borbulevych et al., 1998). As a part of our further structural investigation of this class of compounds (Borbulevych et al., 1998, 1999; Golding et al., 1999; Khrustalev et al., 1996), we present here our results on two polymorphic modifications, (I) and (II), of the title compound, (1). \sch
Although the two polymorphic modifications crystallize in the same space group, namely P21/c, there are two independent molecules, A and B, in the asymmetric unit of form (II), whereas there is only one for form (I). Most bond lengths in (I) and (II) are equal to within three standard uncertainties (Tables 1 and 4). It should be mentioned that in (IIA), the N2—C13 bond is somewhat elongated [1.466 (3) Å], and the O1—C1 bond length of 1.213 (3) Å is shortened, compared with those in (I) and (IIB). On the other hand, the C═O bond is equal to that found in the analogous phenyl-substituted compound, (2) (Borbulevych et al., 1999). The variation in this bond length is attributed to the difference of the hydrogen bonds in compounds (1) and (2) (see below).
The 2-cyanocarboxyaminoprop-2-enylic fragment (N2/C1/O1/C2/C3/C6/N1) in (I) and (II) is rather flattened, despite the presence of shortened intramolecular contacts (Tables 2 and 5). The maximum deviations from the least-squares mean plane passing through all non-H atoms of this fragment are observed for O1 in each case, and equal 0.1430 (8), 0.066 (2) and -0.131 (2) Å for (I), (IIA) and (IIB), respectively.
The main differences between the geometry of the molecules in (I) and (II) are attributed to the degree of rotation of the phenyl ring with the respect to the 2-cyanocarboxyaminoprop-2-enylic fragment. In (I) and (IIB), the C7—C12 ring is considerably twisted, with interplanar angles between these fragments of 34.94 (4) and 43.0 (1)°, respectively. However, in (IIA), the phenyl ring is almost coplanar with the above-mentioned fragment, as shown by the corresponding dihedral angle of 8.9 (1)°. Moreover, where only one IR band (at 1581 cm-1), corresponding to the vibrations of the conjugated fragment PhC≡CCH═C, appears in the IR spectra of (I), two such bands (at 1566 and 1583 cm-1) are seen for (II). We attribute this observation to the presence of two molecules having different rotations of the phenyl ring.
In (I), the molecules are linked into infinite chains through intermolecular hydrogen bonds (Table 3), and similar chains are seen for (II) (Table 6). However, in (II), each chain consists exclusively of molecules of type A or type B. Therefore, molecules of (I) and (II) are not linked into centrosymmetric dimers by intermolecular hydrogen bonding, in contrast with derivatives of 2-cyanopentadien-2,4-oic acid (Borbulevych et al., 1998; Golding et al., 1999). A similar hydrogen-bonding network was observed in (2) (Borbulevych et al., 1999).
In order to allow comparison between the polymorphic forms (I) and (II), calculations of the crystal lattice energies for their crystallographic and optimized structures were carried out using the Dreiding 2.21 force field (Mayo et al., 1990). According to these calculations (see Experimental) the X-ray structure of (I) is more stable than that of (II) by 1.3 kcal mol-1. We attribute this difference mainly to differences in the contribution made by the hydrogen bonding (Table 7). Optimization of the structures of (I) and (II) gives rise to similar results, (I) being more stable than (II) by 1.56 kcal mol-1. In this case, the van der Waals energy contributions are equal, but for (I), the hydrogen-bonding and Coulombic contributions are lower by 1.03 and 0.53 kcal mol-1, respectively. Thus, we conclude that the difference in the lattice energies arises from differences in the energies associated with hydrogen bonding, which appears to be somewhat stronger in (I).
For related literature, see: Borbulevych et al. (1998, 1999); Denchev & Kabaivanov (1993); Golding et al. (1999); Gololobov & Gruber (1997); Khrustalev et al. (1996); Mayo et al. (1990); Molecular (1999); Rappé & Goddard (1991); Shchegolikhin & Lazareva (1997).
Data collection: SMART (Bruker, 1998) for (I); CAD-4 Software (Enraf-Nonius, 1989) for (II). Cell refinement: SMART for (I); CAD-4 Software for (II). Data reduction: SAINT (Bruker, 1998) for (I); CAD-4 Software for (II). For both compounds, program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 1997); software used to prepare material for publication: SHELXTL.
C13H10N2O | Dx = 1.312 Mg m−3 |
Mr = 210.23 | Melting point: 381 K |
Monoclinic, P21/c | Mo Kα radiation, λ = 0.71073 Å |
a = 11.9794 (18) Å | Cell parameters from 540 reflections |
b = 8.9951 (13) Å | θ = 2–24° |
c = 10.0786 (16) Å | µ = 0.09 mm−1 |
β = 101.557 (3)° | T = 110 K |
V = 1064.0 (3) Å3 | Square prism, yellow |
Z = 4 | 0.5 × 0.4 × 0.3 mm |
F(000) = 440 |
Bruker SMART CCD area-detector diffractometer | 2991 independent reflections |
Radiation source: fine-focus sealed tube | 2195 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.032 |
φ and ω scans | θmax = 30.1°, θmin = 1.7° |
Absorption correction: multi-scan (SADABS; Bruker, 1998) | h = −16→8 |
Tmin = 0.958, Tmax = 0.975 | k = −12→12 |
8003 measured reflections | l = −13→14 |
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)] = 0.044 | Hydrogen site location: difference Fourier map |
wR(F2) = 0.116 | All H-atom parameters refined |
S = 0.97 | w = 1/[σ2(Fo2) + (0.077P)2] where P = (Fo2 + 2Fc2)/3 |
2991 reflections | (Δ/σ)max = 0.001 |
185 parameters | Δρmax = 0.29 e Å−3 |
0 restraints | Δρmin = −0.20 e Å−3 |
C13H10N2O | V = 1064.0 (3) Å3 |
Mr = 210.23 | Z = 4 |
Monoclinic, P21/c | Mo Kα radiation |
a = 11.9794 (18) Å | µ = 0.09 mm−1 |
b = 8.9951 (13) Å | T = 110 K |
c = 10.0786 (16) Å | 0.5 × 0.4 × 0.3 mm |
β = 101.557 (3)° |
Bruker SMART CCD area-detector diffractometer | 2991 independent reflections |
Absorption correction: multi-scan (SADABS; Bruker, 1998) | 2195 reflections with I > 2σ(I) |
Tmin = 0.958, Tmax = 0.975 | Rint = 0.032 |
8003 measured reflections |
R[F2 > 2σ(F2)] = 0.044 | 0 restraints |
wR(F2) = 0.116 | All H-atom parameters refined |
S = 0.97 | Δρmax = 0.29 e Å−3 |
2991 reflections | Δρmin = −0.20 e Å−3 |
185 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 | ||
O1 | 0.45358 (7) | 0.25582 (10) | 0.31185 (8) | 0.0277 (2) | |
N1 | 0.69725 (10) | 0.13868 (14) | 0.72697 (11) | 0.0377 (3) | |
N2 | 0.45292 (8) | 0.29913 (10) | 0.53215 (9) | 0.0203 (2) | |
H2 | 0.4751 (13) | 0.2680 (17) | 0.6192 (17) | 0.035 (4)* | |
C1 | 0.49430 (9) | 0.23537 (12) | 0.43267 (11) | 0.0196 (2) | |
C2 | 0.59765 (9) | 0.13833 (11) | 0.47501 (10) | 0.0196 (2) | |
C3 | 0.63525 (9) | 0.05662 (12) | 0.38099 (12) | 0.0230 (2) | |
H3 | 0.5905 (13) | 0.0602 (18) | 0.2920 (17) | 0.038 (4)* | |
C4 | 0.73229 (9) | −0.03567 (12) | 0.40165 (11) | 0.0232 (2) | |
C5 | 0.81166 (9) | −0.11817 (12) | 0.40337 (11) | 0.0222 (2) | |
C6 | 0.65475 (10) | 0.13724 (13) | 0.61427 (12) | 0.0247 (2) | |
C7 | 0.89937 (9) | −0.22331 (12) | 0.39560 (11) | 0.0207 (2) | |
C8 | 1.00752 (10) | −0.21557 (13) | 0.47945 (12) | 0.0239 (2) | |
H8 | 1.0228 (12) | −0.1395 (16) | 0.5478 (15) | 0.026 (3)* | |
C9 | 1.09029 (10) | −0.31896 (14) | 0.46542 (12) | 0.0274 (3) | |
H9 | 1.1645 (13) | −0.3144 (16) | 0.5249 (15) | 0.030 (4)* | |
C10 | 1.06531 (10) | −0.43096 (14) | 0.36945 (13) | 0.0286 (3) | |
H10 | 1.1218 (12) | −0.5026 (17) | 0.3544 (15) | 0.028 (4)* | |
C11 | 0.95755 (11) | −0.44116 (13) | 0.28754 (12) | 0.0276 (3) | |
H11 | 0.9390 (12) | −0.5184 (17) | 0.2246 (16) | 0.033 (4)* | |
C12 | 0.87504 (10) | −0.33771 (13) | 0.29904 (11) | 0.0240 (2) | |
H12 | 0.7981 (13) | −0.3457 (17) | 0.2460 (15) | 0.031 (4)* | |
C13 | 0.35410 (10) | 0.39571 (14) | 0.50063 (12) | 0.0242 (2) | |
H13A | 0.2841 (16) | 0.341 (2) | 0.4605 (19) | 0.052 (5)* | |
H13B | 0.3414 (13) | 0.4378 (18) | 0.5882 (17) | 0.041 (4)* | |
H13C | 0.3675 (13) | 0.4750 (19) | 0.4387 (17) | 0.041 (4)* |
U11 | U22 | U33 | U12 | U13 | U23 | |
O1 | 0.0281 (4) | 0.0365 (5) | 0.0180 (4) | 0.0089 (4) | 0.0033 (3) | 0.0015 (3) |
N1 | 0.0360 (6) | 0.0466 (7) | 0.0274 (5) | 0.0149 (5) | −0.0009 (4) | −0.0019 (5) |
N2 | 0.0211 (4) | 0.0212 (4) | 0.0190 (4) | 0.0020 (3) | 0.0047 (3) | 0.0013 (3) |
C1 | 0.0205 (5) | 0.0191 (5) | 0.0195 (5) | 0.0003 (4) | 0.0047 (4) | 0.0014 (4) |
C2 | 0.0196 (5) | 0.0180 (5) | 0.0213 (5) | −0.0001 (4) | 0.0041 (4) | 0.0020 (4) |
C3 | 0.0227 (5) | 0.0218 (5) | 0.0247 (5) | −0.0001 (4) | 0.0053 (4) | 0.0003 (4) |
C4 | 0.0252 (5) | 0.0202 (5) | 0.0253 (5) | −0.0006 (4) | 0.0075 (4) | −0.0023 (4) |
C5 | 0.0234 (5) | 0.0192 (5) | 0.0248 (5) | −0.0033 (4) | 0.0070 (4) | −0.0010 (4) |
C6 | 0.0235 (5) | 0.0251 (5) | 0.0255 (5) | 0.0064 (4) | 0.0049 (4) | 0.0009 (4) |
C7 | 0.0224 (5) | 0.0180 (5) | 0.0229 (5) | −0.0001 (4) | 0.0078 (4) | 0.0023 (4) |
C8 | 0.0249 (5) | 0.0227 (5) | 0.0241 (5) | −0.0027 (4) | 0.0049 (4) | 0.0013 (4) |
C9 | 0.0216 (5) | 0.0308 (6) | 0.0295 (6) | 0.0015 (4) | 0.0043 (4) | 0.0071 (5) |
C10 | 0.0282 (6) | 0.0281 (6) | 0.0319 (6) | 0.0080 (5) | 0.0116 (5) | 0.0050 (5) |
C11 | 0.0338 (6) | 0.0251 (6) | 0.0256 (5) | 0.0017 (5) | 0.0096 (5) | −0.0029 (5) |
C12 | 0.0239 (5) | 0.0246 (5) | 0.0237 (5) | −0.0002 (4) | 0.0051 (4) | −0.0011 (4) |
C13 | 0.0236 (5) | 0.0234 (5) | 0.0269 (5) | 0.0046 (4) | 0.0080 (4) | 0.0021 (4) |
O1—C1 | 1.2315 (13) | C9—C10 | 1.3871 (18) |
N1—C6 | 1.1480 (16) | C10—C11 | 1.3889 (18) |
N2—C1 | 1.3338 (14) | C11—C12 | 1.3792 (16) |
N2—C13 | 1.4513 (14) | N2—H2 | 0.908 (16) |
C1—C2 | 1.5050 (15) | C3—H3 | 0.949 (17) |
C2—C3 | 1.3462 (15) | C8—H8 | 0.962 (15) |
C2—C6 | 1.4329 (15) | C9—H9 | 0.969 (16) |
C3—C4 | 1.4096 (15) | C10—H10 | 0.968 (15) |
C4—C5 | 1.2035 (15) | C11—H11 | 0.937 (16) |
C5—C7 | 1.4274 (15) | C12—H12 | 0.971 (15) |
C7—C8 | 1.3996 (16) | C13—H13A | 0.984 (19) |
C7—C12 | 1.4062 (16) | C13—H13B | 0.999 (16) |
C8—C9 | 1.3872 (17) | C13—H13C | 0.982 (17) |
O1···H3 | 2.44 (2) | C6···H2 | 2.46 (2) |
C1—N2—C13 | 120.17 (10) | C13—N2—H2 | 117.6 (10) |
O1—C1—N2 | 123.08 (10) | C2—C3—H3 | 116.2 (10) |
O1—C1—C2 | 120.49 (10) | C4—C3—H3 | 116.9 (10) |
N2—C1—C2 | 116.41 (9) | C9—C8—H8 | 120.8 (9) |
C3—C2—C6 | 121.63 (10) | C7—C8—H8 | 119.2 (9) |
C3—C2—C1 | 119.30 (10) | C10—C9—H9 | 120.4 (9) |
C6—C2—C1 | 119.07 (9) | C8—C9—H9 | 119.6 (9) |
C2—C3—C4 | 126.87 (11) | C9—C10—H10 | 122.2 (9) |
C5—C4—C3 | 172.33 (12) | C11—C10—H10 | 117.3 (9) |
C4—C5—C7 | 174.77 (11) | C12—C11—H11 | 118.7 (9) |
N1—C6—C2 | 177.63 (13) | C10—C11—H11 | 121.2 (9) |
C8—C7—C12 | 119.52 (10) | C11—C12—H12 | 121.4 (9) |
C8—C7—C5 | 122.44 (10) | C7—C12—H12 | 118.5 (9) |
C12—C7—C5 | 118.04 (10) | N2—C13—H13A | 112.6 (11) |
C9—C8—C7 | 119.95 (11) | N2—C13—H13B | 107.2 (9) |
C10—C9—C8 | 119.95 (11) | N2—C13—H13C | 110.1 (9) |
C9—C10—C11 | 120.49 (11) | H13A—C13—H13B | 106.4 (14) |
C12—C11—C10 | 120.12 (11) | H13A—C13—H13C | 109.5 (14) |
C11—C12—C7 | 119.95 (11) | H13B—C13—H13C | 111.0 (13) |
C1—N2—H2 | 120.9 (10) | ||
C13—N2—C1—O1 | 1.16 (17) | C12—C7—C8—C9 | 1.01 (16) |
C13—N2—C1—C2 | 179.39 (9) | C5—C7—C8—C9 | −178.60 (10) |
O1—C1—C2—C3 | −9.75 (16) | C7—C8—C9—C10 | −0.79 (17) |
N2—C1—C2—C3 | 171.98 (10) | C8—C9—C10—C11 | −0.42 (18) |
O1—C1—C2—C6 | 169.20 (11) | C9—C10—C11—C12 | 1.42 (18) |
N2—C1—C2—C6 | −9.08 (15) | C10—C11—C12—C7 | −1.19 (18) |
C6—C2—C3—C4 | −1.32 (18) | C8—C7—C12—C11 | −0.02 (17) |
C1—C2—C3—C4 | 177.60 (10) | C5—C7—C12—C11 | 179.61 (11) |
D—H···A | D—H | H···A | D···A | D—H···A |
N2—H2···O1i | 0.91 (2) | 2.02 (2) | 2.860 (1) | 153 (1) |
Symmetry code: (i) x, −y+1/2, z+1/2. |
C13H10N2O | Dx = 1.244 Mg m−3 |
Mr = 210.23 | Melting point: 384 K |
Monoclinic, P21/c | Mo Kα radiation, λ = 0.71073 Å |
a = 22.652 (12) Å | Cell parameters from 24 reflections |
b = 9.728 (7) Å | θ = 10–11° |
c = 10.269 (5) Å | µ = 0.08 mm−1 |
β = 97.29 (4)° | T = 293 K |
V = 2245 (2) Å3 | Needle, yellow |
Z = 8 | 0.5 × 0.2 × 0.2 mm |
F(000) = 880 |
Enraf-Nonius CAD-4 diffractometer | Rint = 0.079 |
Radiation source: fine-focus sealed tube | θmax = 27.0°, θmin = 1.8° |
Graphite monochromator | h = −28→0 |
θ/2θ scans | k = 0→12 |
4929 measured reflections | l = −12→13 |
4810 independent reflections | 2 standard reflections every 90 reflections |
2134 reflections with I > 2σ(I) | intensity decay: 3.4% |
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: difference Fourier map |
wR(F2) = 0.169 | H-atom parameters constrained |
S = 0.96 | w = 1/[σ2(Fo2) + (0.091P)2] where P = (Fo2 + 2Fc2)/3 |
4810 reflections | (Δ/σ)max = 0.001 |
291 parameters | Δρmax = 0.16 e Å−3 |
0 restraints | Δρmin = −0.22 e Å−3 |
C13H10N2O | V = 2245 (2) Å3 |
Mr = 210.23 | Z = 8 |
Monoclinic, P21/c | Mo Kα radiation |
a = 22.652 (12) Å | µ = 0.08 mm−1 |
b = 9.728 (7) Å | T = 293 K |
c = 10.269 (5) Å | 0.5 × 0.2 × 0.2 mm |
β = 97.29 (4)° |
Enraf-Nonius CAD-4 diffractometer | Rint = 0.079 |
4929 measured reflections | 2 standard reflections every 90 reflections |
4810 independent reflections | intensity decay: 3.4% |
2134 reflections with I > 2σ(I) |
R[F2 > 2σ(F2)] = 0.052 | 0 restraints |
wR(F2) = 0.169 | H-atom parameters constrained |
S = 0.96 | Δρmax = 0.16 e Å−3 |
4810 reflections | Δρmin = −0.22 e Å−3 |
291 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 | ||
O1 | 0.51989 (9) | 0.1326 (2) | 0.65637 (18) | 0.0714 (6) | |
N1 | 0.40660 (13) | 0.5274 (3) | 0.5243 (3) | 0.0824 (8) | |
N2 | 0.52030 (9) | 0.3542 (2) | 0.72239 (19) | 0.0545 (6) | |
H2 | 0.5022 | 0.4320 | 0.7122 | 0.065* | |
C1 | 0.50077 (11) | 0.2491 (3) | 0.6456 (2) | 0.0490 (6) | |
C2 | 0.45142 (11) | 0.2854 (3) | 0.5377 (2) | 0.0476 (6) | |
C3 | 0.43153 (11) | 0.1924 (3) | 0.4453 (2) | 0.0555 (7) | |
H3 | 0.4479 | 0.1046 | 0.4507 | 0.067* | |
C4 | 0.38672 (12) | 0.2227 (3) | 0.3404 (2) | 0.0536 (7) | |
C5 | 0.34816 (12) | 0.2549 (3) | 0.2550 (2) | 0.0519 (7) | |
C6 | 0.42675 (12) | 0.4201 (3) | 0.5295 (2) | 0.0558 (7) | |
C7 | 0.30001 (11) | 0.2962 (3) | 0.1603 (2) | 0.0462 (6) | |
C8 | 0.27396 (13) | 0.4228 (3) | 0.1721 (3) | 0.0664 (8) | |
H8 | 0.2894 | 0.4825 | 0.2387 | 0.080* | |
C9 | 0.22506 (14) | 0.4615 (4) | 0.0858 (3) | 0.0778 (9) | |
H9 | 0.2074 | 0.5468 | 0.0946 | 0.093* | |
C10 | 0.20243 (13) | 0.3740 (4) | −0.0132 (3) | 0.0694 (9) | |
H10 | 0.1689 | 0.3994 | −0.0701 | 0.083* | |
C11 | 0.22856 (13) | 0.2512 (3) | −0.0285 (3) | 0.0632 (8) | |
H11 | 0.2138 | 0.1939 | −0.0975 | 0.076* | |
C12 | 0.27716 (12) | 0.2101 (3) | 0.0581 (2) | 0.0546 (7) | |
H12 | 0.2946 | 0.1248 | 0.0479 | 0.066* | |
C13 | 0.57174 (12) | 0.3410 (3) | 0.8237 (3) | 0.0679 (8) | |
H13A | 0.5790 | 0.2455 | 0.8432 | 0.102* | |
H13B | 0.5637 | 0.3880 | 0.9018 | 0.102* | |
H13C | 0.6061 | 0.3807 | 0.7926 | 0.102* | |
O1' | 1.01898 (9) | 0.7563 (2) | 0.68323 (15) | 0.0689 (6) | |
N1' | 0.89839 (14) | 0.6122 (4) | 0.3035 (3) | 0.1193 (14) | |
N2' | 1.01957 (9) | 0.7867 (2) | 0.46670 (17) | 0.0479 (5) | |
H2' | 1.0037 | 0.7650 | 0.3889 | 0.058* | |
C1' | 0.99860 (11) | 0.7301 (3) | 0.5693 (2) | 0.0446 (6) | |
C2' | 0.94784 (10) | 0.6320 (3) | 0.5402 (2) | 0.0455 (6) | |
C3' | 0.92944 (12) | 0.5580 (3) | 0.6369 (2) | 0.0576 (7) | |
H3' | 0.9508 | 0.5691 | 0.7197 | 0.069* | |
C4' | 0.88133 (13) | 0.4649 (3) | 0.6277 (3) | 0.0581 (7) | |
C5' | 0.84124 (13) | 0.3868 (3) | 0.6332 (3) | 0.0554 (7) | |
C6' | 0.91935 (13) | 0.6196 (3) | 0.4093 (3) | 0.0668 (8) | |
C7' | 0.79511 (11) | 0.2901 (3) | 0.6496 (2) | 0.0478 (6) | |
C8' | 0.73735 (12) | 0.3048 (3) | 0.5861 (3) | 0.0588 (7) | |
H8' | 0.7283 | 0.3764 | 0.5269 | 0.071* | |
C9' | 0.69395 (13) | 0.2145 (3) | 0.6104 (3) | 0.0719 (9) | |
H9' | 0.6554 | 0.2252 | 0.5684 | 0.086* | |
C10' | 0.70703 (14) | 0.1083 (3) | 0.6964 (3) | 0.0733 (9) | |
H10' | 0.6772 | 0.0480 | 0.7139 | 0.088* | |
C11' | 0.76401 (14) | 0.0903 (3) | 0.7570 (3) | 0.0699 (8) | |
H11' | 0.7730 | 0.0158 | 0.8129 | 0.084* | |
C12' | 0.80749 (12) | 0.1811 (3) | 0.7356 (3) | 0.0570 (7) | |
H12' | 0.8458 | 0.1699 | 0.7790 | 0.068* | |
C13' | 1.06840 (12) | 0.8841 (3) | 0.4823 (3) | 0.0603 (7) | |
H13D | 1.0622 | 0.9495 | 0.5493 | 0.091* | |
H13E | 1.0702 | 0.9314 | 0.4009 | 0.091* | |
H13F | 1.1051 | 0.8360 | 0.5072 | 0.091* |
U11 | U22 | U33 | U12 | U13 | U23 | |
O1 | 0.0835 (14) | 0.0633 (13) | 0.0603 (12) | 0.0207 (11) | −0.0185 (10) | −0.0021 (10) |
N1 | 0.100 (2) | 0.0637 (18) | 0.0753 (18) | 0.0127 (16) | −0.0191 (15) | 0.0025 (15) |
N2 | 0.0523 (13) | 0.0602 (14) | 0.0472 (12) | 0.0020 (11) | −0.0079 (9) | 0.0056 (11) |
C1 | 0.0486 (14) | 0.0600 (18) | 0.0372 (12) | 0.0031 (13) | 0.0012 (10) | 0.0035 (13) |
C2 | 0.0491 (14) | 0.0542 (16) | 0.0384 (12) | 0.0015 (13) | 0.0015 (10) | 0.0068 (12) |
C3 | 0.0577 (16) | 0.0655 (18) | 0.0417 (13) | 0.0068 (14) | 0.0001 (12) | 0.0023 (13) |
C4 | 0.0570 (16) | 0.0620 (17) | 0.0410 (13) | −0.0002 (14) | 0.0029 (12) | −0.0055 (13) |
C5 | 0.0538 (15) | 0.0637 (18) | 0.0374 (12) | 0.0016 (13) | 0.0034 (12) | 0.0001 (12) |
C6 | 0.0575 (17) | 0.0609 (19) | 0.0457 (14) | −0.0014 (15) | −0.0059 (12) | 0.0058 (14) |
C7 | 0.0517 (14) | 0.0537 (16) | 0.0332 (12) | −0.0066 (13) | 0.0053 (10) | 0.0003 (11) |
C8 | 0.082 (2) | 0.067 (2) | 0.0463 (15) | 0.0068 (17) | −0.0049 (14) | −0.0102 (14) |
C9 | 0.085 (2) | 0.076 (2) | 0.0685 (19) | 0.0271 (18) | −0.0049 (17) | 0.0016 (18) |
C10 | 0.0617 (19) | 0.094 (3) | 0.0497 (16) | 0.0131 (18) | −0.0034 (13) | 0.0090 (17) |
C11 | 0.0592 (17) | 0.085 (2) | 0.0429 (14) | −0.0154 (16) | −0.0048 (12) | −0.0057 (15) |
C12 | 0.0585 (16) | 0.0569 (17) | 0.0477 (14) | −0.0055 (14) | 0.0040 (12) | −0.0053 (13) |
C13 | 0.0569 (17) | 0.086 (2) | 0.0557 (16) | −0.0011 (16) | −0.0146 (13) | −0.0020 (15) |
O1' | 0.0752 (13) | 0.1020 (16) | 0.0283 (8) | −0.0310 (11) | 0.0014 (8) | −0.0067 (9) |
N1' | 0.115 (3) | 0.183 (4) | 0.0527 (16) | −0.072 (2) | −0.0178 (16) | 0.000 (2) |
N2' | 0.0511 (12) | 0.0631 (14) | 0.0287 (9) | −0.0101 (11) | 0.0017 (8) | −0.0056 (10) |
C1' | 0.0490 (14) | 0.0551 (16) | 0.0294 (11) | −0.0039 (12) | 0.0033 (10) | −0.0067 (11) |
C2' | 0.0435 (13) | 0.0585 (16) | 0.0335 (12) | −0.0036 (12) | 0.0013 (10) | −0.0055 (12) |
C3' | 0.0564 (16) | 0.0710 (19) | 0.0436 (14) | −0.0109 (15) | −0.0010 (12) | 0.0047 (14) |
C4' | 0.0615 (18) | 0.0609 (18) | 0.0516 (15) | −0.0017 (16) | 0.0055 (13) | 0.0070 (13) |
C5' | 0.0578 (17) | 0.0577 (17) | 0.0514 (15) | 0.0018 (15) | 0.0097 (12) | 0.0058 (13) |
C6' | 0.0627 (18) | 0.089 (2) | 0.0461 (15) | −0.0277 (16) | −0.0028 (13) | −0.0014 (15) |
C7' | 0.0516 (15) | 0.0491 (15) | 0.0432 (13) | 0.0015 (12) | 0.0088 (11) | −0.0003 (12) |
C8' | 0.0647 (18) | 0.0573 (17) | 0.0514 (15) | 0.0020 (15) | −0.0036 (13) | 0.0037 (13) |
C9' | 0.0526 (17) | 0.086 (2) | 0.074 (2) | −0.0091 (17) | −0.0054 (14) | −0.0035 (19) |
C10' | 0.070 (2) | 0.072 (2) | 0.081 (2) | −0.0176 (17) | 0.0198 (17) | 0.0017 (18) |
C11' | 0.075 (2) | 0.069 (2) | 0.0672 (18) | −0.0007 (17) | 0.0146 (16) | 0.0179 (16) |
C12' | 0.0596 (17) | 0.0593 (17) | 0.0515 (15) | 0.0030 (14) | 0.0046 (12) | 0.0060 (13) |
C13' | 0.0591 (17) | 0.073 (2) | 0.0506 (14) | −0.0145 (15) | 0.0117 (13) | −0.0041 (14) |
O1—C1 | 1.213 (3) | C7'—C12' | 1.385 (4) |
N1—C6 | 1.138 (4) | C7'—C8' | 1.393 (4) |
N2—C1 | 1.332 (3) | C8'—C9' | 1.365 (4) |
N2—C13 | 1.466 (3) | C9'—C10' | 1.366 (4) |
C1—C2 | 1.513 (3) | C10'—C11' | 1.371 (4) |
C2—C3 | 1.346 (4) | C11'—C12' | 1.362 (4) |
C2—C6 | 1.423 (4) | N2—H2 | 0.8600 |
C3—C4 | 1.414 (4) | C3—H3 | 0.9300 |
C4—C5 | 1.199 (3) | C8—H8 | 0.9300 |
C5—C7 | 1.424 (4) | C9—H9 | 0.9300 |
C7—C8 | 1.378 (4) | C10—H10 | 0.9300 |
C7—C12 | 1.391 (3) | C11—H11 | 0.9300 |
C8—C9 | 1.381 (4) | C12—H12 | 0.9300 |
C9—C10 | 1.375 (4) | C13—H13A | 0.9600 |
C10—C11 | 1.351 (4) | C13—H13B | 0.9600 |
C11—C12 | 1.383 (4) | C13—H13C | 0.9600 |
O1'—C1' | 1.228 (3) | N2'—H2' | 0.8600 |
N1'—C6' | 1.131 (3) | C3'—H3' | 0.9300 |
N2'—C1' | 1.329 (3) | C8'—H8' | 0.9300 |
N2'—C13' | 1.450 (3) | C9'—H9' | 0.9300 |
C1'—C2' | 1.495 (3) | C10'—H10' | 0.9300 |
C2'—C3' | 1.335 (3) | C11'—H11' | 0.9300 |
C2'—C6' | 1.420 (3) | C12'—H12' | 0.9300 |
C3'—C4' | 1.411 (4) | C13'—H13D | 0.9600 |
C4'—C5' | 1.191 (4) | C13'—H13E | 0.9600 |
C5'—C7' | 1.432 (4) | C13'—H13F | 0.9600 |
C6···H2 | 2.38 | C6'···H2' | 2.41 |
O1'···H3' | 2.45 | ||
C1—N2—C13 | 121.8 (2) | C13—N2—H2 | 119.1 |
O1—C1—N2 | 125.1 (2) | C2—C3—H3 | 118.6 |
O1—C1—C2 | 120.4 (2) | C4—C3—H3 | 118.6 |
N2—C1—C2 | 114.5 (2) | C7—C8—H8 | 119.8 |
C3—C2—C6 | 118.9 (2) | C9—C8—H8 | 119.8 |
C3—C2—C1 | 120.7 (2) | C10—C9—H9 | 120.0 |
C6—C2—C1 | 120.4 (2) | C8—C9—H9 | 120.0 |
C2—C3—C4 | 122.7 (3) | C11—C10—H10 | 119.8 |
C5—C4—C3 | 176.4 (3) | C9—C10—H10 | 119.8 |
C4—C5—C7 | 176.1 (3) | C10—C11—H11 | 119.8 |
N1—C6—C2 | 179.1 (3) | C12—C11—H11 | 119.8 |
C8—C7—C12 | 118.9 (2) | C11—C12—H12 | 120.0 |
C8—C7—C5 | 119.4 (2) | C7—C12—H12 | 120.0 |
C12—C7—C5 | 121.7 (2) | N2—C13—H13A | 109.5 |
C7—C8—C9 | 120.3 (3) | N2—C13—H13B | 109.5 |
C10—C9—C8 | 120.0 (3) | N2—C13—H13C | 109.5 |
C11—C10—C9 | 120.4 (3) | H13A—C13—H13B | 109.5 |
C10—C11—C12 | 120.4 (3) | H13A—C13—H13C | 109.5 |
C11—C12—C7 | 120.0 (3) | H13B—C13—H13C | 109.5 |
C1'—N2'—C13' | 121.8 (2) | C1'—N2'—H2' | 119.1 |
O1'—C1'—N2' | 122.7 (2) | C13'—N2'—H2' | 119.1 |
O1'—C1'—C2' | 120.7 (2) | C2'—C3'—H3' | 116.3 |
N2'—C1'—C2' | 116.7 (2) | C4'—C3'—H3' | 116.3 |
C3'—C2'—C6' | 120.7 (2) | C9'—C8'—H8' | 119.9 |
C3'—C2'—C1' | 120.0 (2) | C7'—C8'—H8' | 119.9 |
C6'—C2'—C1' | 119.3 (2) | C8'—C9'—H9' | 119.9 |
C2'—C3'—C4' | 127.5 (2) | C10'—C9'—H9' | 119.9 |
C5'—C4'—C3' | 173.5 (3) | C9'—C10'—H10' | 119.8 |
C4'—C5'—C7' | 175.7 (3) | C11'—C10'—H10' | 119.8 |
N1'—C6'—C2' | 177.4 (3) | C12'—C11'—H11' | 119.9 |
C12'—C7'—C8' | 118.6 (3) | C10'—C11'—H11' | 119.9 |
C12'—C7'—C5' | 119.1 (2) | C11'—C12'—H12' | 119.7 |
C8'—C7'—C5' | 122.2 (2) | C7'—C12'—H12' | 119.7 |
C9'—C8'—C7' | 120.2 (3) | N2'—C13'—H13D | 109.5 |
C8'—C9'—C10' | 120.2 (3) | N2'—C13'—H13E | 109.5 |
C9'—C10'—C11' | 120.3 (3) | N2'—C13'—H13F | 109.5 |
C12'—C11'—C10' | 120.1 (3) | H13D—C13'—H13E | 109.5 |
C11'—C12'—C7' | 120.5 (3) | H13D—C13'—H13F | 109.5 |
C1—N2—H2 | 119.1 | H13E—C13'—H13F | 109.5 |
C13—N2—C1—O1 | 5.3 (4) | C13'—N2'—C1'—O1' | 0.1 (4) |
C13—N2—C1—C2 | −174.0 (2) | C13'—N2'—C1'—C2' | 179.6 (2) |
O1—C1—C2—C3 | −5.8 (4) | O1'—C1'—C2'—C3' | −9.1 (4) |
N2—C1—C2—C3 | 173.5 (2) | N2'—C1'—C2'—C3' | 171.5 (2) |
O1—C1—C2—C6 | 176.5 (3) | O1'—C1'—C2'—C6' | 170.4 (3) |
N2—C1—C2—C6 | −4.2 (3) | N2'—C1'—C2'—C6' | −9.1 (4) |
C6—C2—C3—C4 | −0.4 (4) | C6'—C2'—C3'—C4' | −1.8 (5) |
C1—C2—C3—C4 | −178.2 (2) | C1'—C2'—C3'—C4' | 177.7 (3) |
C12—C7—C8—C9 | 1.6 (4) | C12'—C7'—C8'—C9' | 1.1 (4) |
C5—C7—C8—C9 | −176.3 (3) | C5'—C7'—C8'—C9' | −176.2 (3) |
C7—C8—C9—C10 | −0.5 (5) | C7'—C8'—C9'—C10' | −0.6 (5) |
C8—C9—C10—C11 | −1.4 (5) | C8'—C9'—C10'—C11' | −1.2 (5) |
C9—C10—C11—C12 | 2.2 (5) | C9'—C10'—C11'—C12' | 2.4 (5) |
C10—C11—C12—C7 | −1.0 (4) | C10'—C11'—C12'—C7' | −1.9 (4) |
C8—C7—C12—C11 | −0.9 (4) | C8'—C7'—C12'—C11' | 0.2 (4) |
C5—C7—C12—C11 | 176.9 (2) | C5'—C7'—C12'—C11' | 177.5 (3) |
D—H···A | D—H | H···A | D···A | D—H···A |
N2—H2···O1i | 0.86 | 2.46 | 3.163 (4) | 139 |
N2′—H2′···O1′ii | 0.86 | 2.19 | 2.939 (3) | 145 |
Symmetry codes: (i) −x+1, y+1/2, −z+3/2; (ii) x, −y+3/2, z−1/2. |
Experimental details
(I) | (II) | |
Crystal data | ||
Chemical formula | C13H10N2O | C13H10N2O |
Mr | 210.23 | 210.23 |
Crystal system, space group | Monoclinic, P21/c | Monoclinic, P21/c |
Temperature (K) | 110 | 293 |
a, b, c (Å) | 11.9794 (18), 8.9951 (13), 10.0786 (16) | 22.652 (12), 9.728 (7), 10.269 (5) |
β (°) | 101.557 (3) | 97.29 (4) |
V (Å3) | 1064.0 (3) | 2245 (2) |
Z | 4 | 8 |
Radiation type | Mo Kα | Mo Kα |
µ (mm−1) | 0.09 | 0.08 |
Crystal size (mm) | 0.5 × 0.4 × 0.3 | 0.5 × 0.2 × 0.2 |
Data collection | ||
Diffractometer | Bruker SMART CCD area-detector | Enraf-Nonius CAD-4 |
Absorption correction | Multi-scan (SADABS; Bruker, 1998) | – |
Tmin, Tmax | 0.958, 0.975 | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 8003, 2991, 2195 | 4929, 4810, 2134 |
Rint | 0.032 | 0.079 |
(sin θ/λ)max (Å−1) | 0.705 | 0.639 |
Refinement | ||
R[F2 > 2σ(F2)], wR(F2), S | 0.044, 0.116, 0.97 | 0.052, 0.169, 0.96 |
No. of reflections | 2991 | 4810 |
No. of parameters | 185 | 291 |
H-atom treatment | All H-atom parameters refined | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.29, −0.20 | 0.16, −0.22 |
Computer programs: SMART (Bruker, 1998), CAD-4 Software (Enraf-Nonius, 1989), SMART, CAD-4 Software, SAINT (Bruker, 1998), SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), SHELXTL (Bruker, 1997), SHELXTL.
O1—C1 | 1.2315 (13) | C2—C3 | 1.3462 (15) |
N1—C6 | 1.1480 (16) | C2—C6 | 1.4329 (15) |
N2—C1 | 1.3338 (14) | C3—C4 | 1.4096 (15) |
N2—C13 | 1.4513 (14) | C4—C5 | 1.2035 (15) |
C1—C2 | 1.5050 (15) | C5—C7 | 1.4274 (15) |
O1···H3 | 2.44 (2) | C6···H2 | 2.46 (2) |
D—H···A | D—H | H···A | D···A | D—H···A |
N2—H2···O1i | 0.91 (2) | 2.02 (2) | 2.860 (1) | 153 (1) |
Symmetry code: (i) x, −y+1/2, z+1/2. |
O1—C1 | 1.213 (3) | O1'—C1' | 1.228 (3) |
N1—C6 | 1.138 (4) | N1'—C6' | 1.131 (3) |
N2—C1 | 1.332 (3) | N2'—C1' | 1.329 (3) |
N2—C13 | 1.466 (3) | N2'—C13' | 1.450 (3) |
C1—C2 | 1.513 (3) | C1'—C2' | 1.495 (3) |
C2—C3 | 1.346 (4) | C2'—C3' | 1.335 (3) |
C2—C6 | 1.423 (4) | C2'—C6' | 1.420 (3) |
C3—C4 | 1.414 (4) | C3'—C4' | 1.411 (4) |
C4—C5 | 1.199 (3) | C4'—C5' | 1.191 (4) |
C5—C7 | 1.424 (4) | C5'—C7' | 1.432 (4) |
C6···H2 | 2.38 | C6'···H2' | 2.41 |
O1'···H3' | 2.45 |
D—H···A | D—H | H···A | D···A | D—H···A |
N2—H2···O1i | 0.86 | 2.46 | 3.163 (4) | 139.3 |
N2'—H2'···O1'ii | 0.86 | 2.19 | 2.939 (3) | 145.1 |
Symmetry codes: (i) −x+1, y+1/2, −z+3/2; (ii) x, −y+3/2, z−1/2. |
Energy | (1) (I)a | (1) (I)b | (1) (II)a | (1) (II)b |
Total | -28.15 | -29.21 | -26.85 | -27.65 |
van der Waals | -21.57 | -22.34 | -21.83 | -22.34 |
Coulombic | -4.22 | -4.42 | -3.70 | -3.89 |
Hydrogen bonding | -2.36 | -2.45 | -1.32 | -1.42 |
a crystallographic structure b optimised structure |
Derivatives of 2-cyanoacrylic acid with unsaturated substitutents in the 3-position are of great interest because of their potential bioactivity and versatility in the synthesis of polymeric and heterocyxlic compounds. For example, such compounds can undergo polymerization under very mild conditions (Gololobov & Gruber, 1997; Denchev & Kabaivanov, 1993). In addition, our previous structural studies show that topochemical reactions can occur in some of these derivatives, namely in 2-cyano-(2E)-pentadien-2,4-oic acid and its ethyl ester (Borbulevych et al., 1998). As a part of our further structural investigation of this class of compounds (Borbulevych et al., 1998, 1999; Golding et al., 1999; Khrustalev et al., 1996), we present here our results on two polymorphic modifications, (I) and (II), of the title compound, (1). \sch
Although the two polymorphic modifications crystallize in the same space group, namely P21/c, there are two independent molecules, A and B, in the asymmetric unit of form (II), whereas there is only one for form (I). Most bond lengths in (I) and (II) are equal to within three standard uncertainties (Tables 1 and 4). It should be mentioned that in (IIA), the N2—C13 bond is somewhat elongated [1.466 (3) Å], and the O1—C1 bond length of 1.213 (3) Å is shortened, compared with those in (I) and (IIB). On the other hand, the C═O bond is equal to that found in the analogous phenyl-substituted compound, (2) (Borbulevych et al., 1999). The variation in this bond length is attributed to the difference of the hydrogen bonds in compounds (1) and (2) (see below).
The 2-cyanocarboxyaminoprop-2-enylic fragment (N2/C1/O1/C2/C3/C6/N1) in (I) and (II) is rather flattened, despite the presence of shortened intramolecular contacts (Tables 2 and 5). The maximum deviations from the least-squares mean plane passing through all non-H atoms of this fragment are observed for O1 in each case, and equal 0.1430 (8), 0.066 (2) and -0.131 (2) Å for (I), (IIA) and (IIB), respectively.
The main differences between the geometry of the molecules in (I) and (II) are attributed to the degree of rotation of the phenyl ring with the respect to the 2-cyanocarboxyaminoprop-2-enylic fragment. In (I) and (IIB), the C7—C12 ring is considerably twisted, with interplanar angles between these fragments of 34.94 (4) and 43.0 (1)°, respectively. However, in (IIA), the phenyl ring is almost coplanar with the above-mentioned fragment, as shown by the corresponding dihedral angle of 8.9 (1)°. Moreover, where only one IR band (at 1581 cm-1), corresponding to the vibrations of the conjugated fragment PhC≡CCH═C, appears in the IR spectra of (I), two such bands (at 1566 and 1583 cm-1) are seen for (II). We attribute this observation to the presence of two molecules having different rotations of the phenyl ring.
In (I), the molecules are linked into infinite chains through intermolecular hydrogen bonds (Table 3), and similar chains are seen for (II) (Table 6). However, in (II), each chain consists exclusively of molecules of type A or type B. Therefore, molecules of (I) and (II) are not linked into centrosymmetric dimers by intermolecular hydrogen bonding, in contrast with derivatives of 2-cyanopentadien-2,4-oic acid (Borbulevych et al., 1998; Golding et al., 1999). A similar hydrogen-bonding network was observed in (2) (Borbulevych et al., 1999).
In order to allow comparison between the polymorphic forms (I) and (II), calculations of the crystal lattice energies for their crystallographic and optimized structures were carried out using the Dreiding 2.21 force field (Mayo et al., 1990). According to these calculations (see Experimental) the X-ray structure of (I) is more stable than that of (II) by 1.3 kcal mol-1. We attribute this difference mainly to differences in the contribution made by the hydrogen bonding (Table 7). Optimization of the structures of (I) and (II) gives rise to similar results, (I) being more stable than (II) by 1.56 kcal mol-1. In this case, the van der Waals energy contributions are equal, but for (I), the hydrogen-bonding and Coulombic contributions are lower by 1.03 and 0.53 kcal mol-1, respectively. Thus, we conclude that the difference in the lattice energies arises from differences in the energies associated with hydrogen bonding, which appears to be somewhat stronger in (I).