Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270111043083/gz3202sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270111043083/gz3202Isup2.hkl | |
Chemical Markup Language (CML) file https://doi.org/10.1107/S0108270111043083/gz3202Isup3.cml |
CCDC reference: 855976
The syntheses of (3-bromo-2-thienyl)-trimethylsilane (Fröhlich & Kalt, 1990) and azidobenzene (Cwiklicki & Rehse, 2004) were performed according to previously reported methods. All other chemicals were obtained commercially and used without purification. The precursor (Z)-trimethyl(4-(methylthio)but-3-en-1-inyl)silane was prepared by analogy with the pentane compound (Lumpi et al., 2011): to a solution of (3-bromo-2-thienyl)trimethylsilane (1.88 g, 8.0 mmol) in dry Et2O (30 ml, 0.3 M) under an argon atmosphere at 203 K, n-BuLi (3.5 ml, 8.8 mmol; 2.5 M solution in hexanes) was added over a period of 15 min and the mixture stirred for 1 h. The mixture was then warmed to 283 K, stirred for 1 h, cooled to 273 K and MeI (2.50 g, 17.6 mmol) was added. After 1 h at room temperature, the mixture was poured onto a half-saturated NH4Cl solution and extracted with Et2O. The organic layer was washed with brine, dried over anhydrous Na2SO4 and concentrated. Column chromatography [light petroleum, dichloromethane (1→ 4%)] yielded 0.685 g (50%) of trimethyl[4-(methylthio)but-3-en-1-inyl]silane, (II)? as a slightly yellow liquid. Spectroscopic analysis: 1H NMR (200 MHz, CDCl3, δ, p.p.m.): 6.49 (d, J = 10.0 Hz, 1H), 5.49 (d, J = 10.0 Hz, 1H), 2.38 (s, 3H), 0.20 (s, 9H); 13C NMR (50 MHz, CDCl3, δ, p.p.m.): 143.1 (d), 104.5 (d), 102.9 (s), 101.2 (s), 16.8 (q), -0.1 (q). Analysis, calculated for C8H14SSi: m/z 171.0658 [M+H]+; ound: MS (APCI): m/z 171.0686 [M+H]+.
The title compound was prepared by analogy with the propyl compound (Lumpi et al., 2011): To a suspension of (II) (0.427 g, 2.51 mmol, 1.00 equivalent), azidobenzene (0.372 g, 3.12 mmol, 1.25 equivalent), CuSO4.5H2O (0.125 g, 0.50 mmol, 20 mol%) and sodium ascorbate (0.200 g, 1.01 mmol, 40 mol%) in t-BuOH–H2O (1:1 v/v, 6.3 ml, 0.4 M) was added potassium fluoride (0.169 g, 2.91 mmol, 1.16 equivalent). The reaction vessel was sealed and heated at 323 K for 18 h. The reaction mixture was then diluted with water and extracted with Et2O. The combined organic layers were washed with brine and dried over anhydrous Na2SO4. Suction filtration and evaporation of the solvent, followed by column chromatography (light petroleum–Et2O, 3:1 v/v) and crystallization from n-hexane, afforded (I) (0.386 g, 71%) as a white solid. Single crystals were obtained by recrystallization from n-hexane (m.p. 362.9–362.2 K). Spectroscopic analysis: 1H NMR (400 MHz, CD2Cl2, δ, p.p.m.): 8.21 (s, 1H), 7.77 (d, J = 8.0 Hz, 2H), 7.55 (t, J = 7.8 Hz, 2H), 7.46 (t, J = 7.4 Hz, 1H), 6.65 (d, J = 10.8 Hz, 1H), 6.43 (d, J = 10.6 Hz, 1H), 2.48 (s, 3H); 13C NMR (100 MHz, CD2Cl2, δ, p.p.m.): 145.8 (s), 137.6 (s), 131.3 (d), 130.3 (d), 129.1 (d), 121.0 (d), 120.4 (d), 114.5 (d), 18.6 (q). Analysis, calculated for C11H11N3S: m/z 218.0746 [M+H]+; found: MS (ESI): m/z 218.0756 [M+H]+.
Of five crystals analysed, all were twinned. The reflections of the two twin mates were separated using the RLATT software (Bruker, 2008). In all cases, the twin domains were related by mirroring at (001). The final cell parameters were refined during data reduction with SAINT-Plus (Bruker, 2008). The parameters of both twin domains were restrained to the same values.
The twin index is 10.98 ≈ 11, although besides reflections |l| = 0, 11, reflections |l| = 1, 2, 9, 10, 12, 13 are also partially overlapping (Fig. 4). Minor diffuse scattering along a* (Fig. 4), indicating disorder in the stacking direction, was neglected.
The structure was solved using direct methods on a dataset with averaged equivalent reflections of both twin mates. Refinement was performed using the reflections of the larger twin domain. All non-H atoms were refined with anisotropic displacement parameters. The parameters of all H atoms were fully refined. No suspicious electron density was found in the difference Fourier maps of the final refinement cycles. The twin volume fraction was refined from overlapping reflections to 0.4232 (13).
Data collection: APEX2 (Bruker, 2008); cell refinement: SAINT-Plus (Bruker, 2008); data reduction: SAINT-Plus (Bruker, 2008); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ATOMS (Dowty, 2006) and Mercury (Macrae et al., 2008); software used to prepare material for publication: publCIF (Westrip, 2010).
C11H11N3S | F(000) = 456 |
Mr = 217.29 | Dx = 1.354 Mg m−3 |
Monoclinic, P21/c | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2ybc | Cell parameters from 33824 reflections |
a = 12.6198 (3) Å | θ = 3.2–33.0° |
b = 7.8465 (2) Å | µ = 0.27 mm−1 |
c = 10.7699 (3) Å | T = 100 K |
β = 92.2261 (17)° | Block, colourless |
V = 1065.64 (5) Å3 | 0.45 × 0.38 × 0.22 mm |
Z = 4 |
Bruker APEXII CCD area-detector diffractometer | 4678 independent reflections |
Radiation source: fine-focus sealed tube | 3654 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.000 |
ω and ϕ scans | θmax = 35.0°, θmin = 3.1° |
Absorption correction: multi-scan (TWINABS; Bruker, 2008) | h = −20→20 |
Tmin = 0.888, Tmax = 0.943 | k = 0→12 |
4678 measured reflections | l = 0→17 |
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)] = 0.048 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.111 | All H-atom parameters refined |
S = 1.03 | w = 1/[σ2(Fo2) + (0.052P)2 + 0.2445P] where P = (Fo2 + 2Fc2)/3 |
4678 reflections | (Δ/σ)max = 0.001 |
181 parameters | Δρmax = 0.46 e Å−3 |
0 restraints | Δρmin = −0.30 e Å−3 |
C11H11N3S | V = 1065.64 (5) Å3 |
Mr = 217.29 | Z = 4 |
Monoclinic, P21/c | Mo Kα radiation |
a = 12.6198 (3) Å | µ = 0.27 mm−1 |
b = 7.8465 (2) Å | T = 100 K |
c = 10.7699 (3) Å | 0.45 × 0.38 × 0.22 mm |
β = 92.2261 (17)° |
Bruker APEXII CCD area-detector diffractometer | 4678 independent reflections |
Absorption correction: multi-scan (TWINABS; Bruker, 2008) | 3654 reflections with I > 2σ(I) |
Tmin = 0.888, Tmax = 0.943 | Rint = 0.000 |
4678 measured reflections |
R[F2 > 2σ(F2)] = 0.048 | 0 restraints |
wR(F2) = 0.111 | All H-atom parameters refined |
S = 1.03 | Δρmax = 0.46 e Å−3 |
4678 reflections | Δρmin = −0.30 e Å−3 |
181 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 | ||
S1 | 1.11275 (3) | 0.06567 (5) | 0.24849 (4) | 0.02233 (9) | |
N1 | 0.76293 (9) | 0.07888 (16) | 0.13468 (11) | 0.0156 (2) | |
N2 | 0.74046 (10) | 0.17066 (17) | 0.03057 (12) | 0.0199 (2) | |
N3 | 0.83021 (9) | 0.23483 (18) | −0.00556 (13) | 0.0202 (2) | |
C1 | 0.67935 (11) | −0.00333 (17) | 0.19711 (13) | 0.0151 (2) | |
C2 | 0.68245 (11) | −0.00616 (18) | 0.32607 (13) | 0.0165 (2) | |
C3 | 0.59907 (12) | −0.0831 (2) | 0.38561 (16) | 0.0195 (3) | |
C4 | 0.51418 (12) | −0.1536 (2) | 0.31755 (16) | 0.0221 (3) | |
C5 | 0.51264 (12) | −0.14945 (19) | 0.18873 (16) | 0.0223 (3) | |
C6 | 0.59556 (12) | −0.0745 (2) | 0.12726 (15) | 0.0191 (3) | |
C7 | 0.86800 (11) | 0.08507 (18) | 0.16592 (13) | 0.0161 (2) | |
C8 | 0.91130 (11) | 0.18438 (18) | 0.07486 (13) | 0.0169 (2) | |
C9 | 1.01917 (12) | 0.2334 (2) | 0.04973 (15) | 0.0201 (3) | |
C10 | 1.10794 (12) | 0.1882 (2) | 0.11396 (14) | 0.0190 (3) | |
C11 | 1.25224 (11) | 0.0187 (2) | 0.26357 (17) | 0.0219 (3) | |
H2 | 0.7429 (16) | 0.046 (3) | 0.3721 (18) | 0.019 (5)* | |
H3 | 0.6006 (17) | −0.080 (3) | 0.472 (2) | 0.025 (5)* | |
H4 | 0.4539 (16) | −0.205 (3) | 0.3587 (18) | 0.021 (5)* | |
H5 | 0.4519 (18) | −0.195 (3) | 0.1368 (19) | 0.028 (5)* | |
H6 | 0.5978 (18) | −0.071 (3) | 0.041 (2) | 0.027 (6)* | |
H7 | 0.8937 (13) | 0.033 (2) | 0.2386 (17) | 0.016 (4)* | |
H9 | 1.0267 (16) | 0.298 (3) | −0.0234 (19) | 0.024 (5)* | |
H10 | 1.1741 (16) | 0.220 (3) | 0.0855 (19) | 0.027 (5)* | |
H111 | 1.2940 (17) | 0.121 (3) | 0.261 (2) | 0.035 (6)* | |
H112 | 1.2634 (18) | −0.032 (3) | 0.344 (2) | 0.030 (6)* | |
H113 | 1.2710 (19) | −0.052 (3) | 0.197 (2) | 0.039 (6)* |
U11 | U22 | U33 | U12 | U13 | U23 | |
S1 | 0.01557 (14) | 0.03192 (19) | 0.01967 (17) | 0.00330 (13) | 0.00304 (13) | 0.00579 (15) |
N1 | 0.0145 (5) | 0.0172 (5) | 0.0149 (5) | 0.0000 (4) | −0.0022 (4) | 0.0007 (4) |
N2 | 0.0200 (6) | 0.0222 (6) | 0.0171 (6) | 0.0030 (5) | −0.0029 (4) | 0.0026 (5) |
N3 | 0.0189 (5) | 0.0230 (6) | 0.0185 (6) | 0.0026 (5) | −0.0009 (5) | 0.0028 (5) |
C1 | 0.0124 (5) | 0.0135 (5) | 0.0193 (6) | 0.0005 (4) | −0.0015 (5) | −0.0014 (5) |
C2 | 0.0150 (6) | 0.0157 (6) | 0.0187 (6) | 0.0007 (5) | −0.0015 (5) | −0.0020 (5) |
C3 | 0.0175 (6) | 0.0180 (6) | 0.0233 (8) | 0.0005 (5) | 0.0028 (5) | 0.0008 (5) |
C4 | 0.0153 (6) | 0.0173 (6) | 0.0339 (8) | −0.0012 (5) | 0.0028 (6) | −0.0002 (6) |
C5 | 0.0150 (6) | 0.0173 (6) | 0.0341 (8) | −0.0012 (5) | −0.0058 (6) | −0.0033 (6) |
C6 | 0.0164 (6) | 0.0178 (6) | 0.0226 (7) | 0.0004 (5) | −0.0052 (5) | −0.0035 (5) |
C7 | 0.0132 (5) | 0.0188 (6) | 0.0163 (6) | −0.0002 (5) | −0.0013 (4) | 0.0018 (5) |
C8 | 0.0181 (6) | 0.0165 (6) | 0.0162 (6) | 0.0010 (5) | −0.0010 (5) | 0.0008 (5) |
C9 | 0.0204 (6) | 0.0204 (7) | 0.0196 (7) | −0.0018 (5) | 0.0024 (5) | 0.0042 (5) |
C10 | 0.0176 (6) | 0.0210 (6) | 0.0186 (6) | −0.0018 (5) | 0.0035 (5) | 0.0010 (5) |
C11 | 0.0153 (5) | 0.0256 (7) | 0.0246 (7) | 0.0007 (5) | −0.0025 (5) | 0.0001 (6) |
S1—C10 | 1.7378 (15) | C4—H4 | 0.98 (2) |
S1—C11 | 1.7997 (14) | C5—C6 | 1.390 (2) |
N1—N2 | 1.3534 (17) | C5—H5 | 1.00 (2) |
N1—C7 | 1.3561 (18) | C6—H6 | 0.93 (2) |
N1—C1 | 1.4268 (18) | C7—C8 | 1.382 (2) |
N2—N3 | 1.3122 (18) | C7—H7 | 0.930 (18) |
N3—C8 | 1.3730 (19) | C8—C9 | 1.450 (2) |
C1—C2 | 1.388 (2) | C9—C10 | 1.341 (2) |
C1—C6 | 1.3907 (19) | C9—H9 | 0.94 (2) |
C2—C3 | 1.391 (2) | C10—H10 | 0.93 (2) |
C2—H2 | 0.98 (2) | C11—H111 | 0.96 (2) |
C3—C4 | 1.389 (2) | C11—H112 | 0.96 (2) |
C3—H3 | 0.93 (2) | C11—H113 | 0.94 (2) |
C4—C5 | 1.387 (2) | ||
C10—S1—C11 | 101.00 (8) | C5—C6—C1 | 118.87 (15) |
N2—N1—C7 | 110.97 (12) | C5—C6—H6 | 122.7 (14) |
N2—N1—C1 | 119.74 (11) | C1—C6—H6 | 118.4 (14) |
C7—N1—C1 | 129.26 (12) | N1—C7—C8 | 104.71 (12) |
N3—N2—N1 | 107.12 (12) | N1—C7—H7 | 119.9 (11) |
N2—N3—C8 | 109.45 (12) | C8—C7—H7 | 135.3 (11) |
C2—C1—C6 | 121.74 (14) | N3—C8—C7 | 107.74 (12) |
C2—C1—N1 | 119.09 (13) | N3—C8—C9 | 119.20 (13) |
C6—C1—N1 | 119.15 (13) | C7—C8—C9 | 133.00 (13) |
C1—C2—C3 | 118.41 (14) | C10—C9—C8 | 127.21 (14) |
C1—C2—H2 | 119.3 (11) | C10—C9—H9 | 117.6 (13) |
C3—C2—H2 | 122.3 (11) | C8—C9—H9 | 115.0 (13) |
C4—C3—C2 | 120.74 (15) | C9—C10—S1 | 125.30 (12) |
C4—C3—H3 | 121.5 (13) | C9—C10—H10 | 120.0 (13) |
C2—C3—H3 | 117.7 (13) | S1—C10—H10 | 114.7 (13) |
C5—C4—C3 | 119.94 (15) | S1—C11—H111 | 111.3 (13) |
C5—C4—H4 | 118.7 (12) | S1—C11—H112 | 106.0 (13) |
C3—C4—H4 | 121.3 (12) | H111—C11—H112 | 108.2 (19) |
C4—C5—C6 | 120.30 (15) | S1—C11—H113 | 109.0 (15) |
C4—C5—H5 | 122.2 (12) | H111—C11—H113 | 108 (2) |
C6—C5—H5 | 117.4 (12) | H112—C11—H113 | 114 (2) |
C9—C10—S1—C11 | 168.40 (15) |
D—H···A | D—H | H···A | D···A | D—H···A |
C11—H113···N2i | 0.94 (2) | 2.62 (3) | 3.503 (2) | 156 (2) |
C2—H2···N3ii | 0.98 (2) | 2.41 (2) | 3.3220 (19) | 154.6 (17) |
Symmetry codes: (i) −x+2, −y, −z; (ii) x, −y+1/2, z+1/2. |
Experimental details
Crystal data | |
Chemical formula | C11H11N3S |
Mr | 217.29 |
Crystal system, space group | Monoclinic, P21/c |
Temperature (K) | 100 |
a, b, c (Å) | 12.6198 (3), 7.8465 (2), 10.7699 (3) |
β (°) | 92.2261 (17) |
V (Å3) | 1065.64 (5) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.27 |
Crystal size (mm) | 0.45 × 0.38 × 0.22 |
Data collection | |
Diffractometer | Bruker APEXII CCD area-detector diffractometer |
Absorption correction | Multi-scan (TWINABS; Bruker, 2008) |
Tmin, Tmax | 0.888, 0.943 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 4678, 4678, 3654 |
Rint | 0.000 |
(sin θ/λ)max (Å−1) | 0.806 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.048, 0.111, 1.03 |
No. of reflections | 4678 |
No. of parameters | 181 |
H-atom treatment | All H-atom parameters refined |
Δρmax, Δρmin (e Å−3) | 0.46, −0.30 |
Computer programs: APEX2 (Bruker, 2008), SAINT-Plus (Bruker, 2008), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), ATOMS (Dowty, 2006) and Mercury (Macrae et al., 2008), publCIF (Westrip, 2010).
D—H···A | D—H | H···A | D···A | D—H···A |
C11—H113···N2i | 0.94 (2) | 2.62 (3) | 3.503 (2) | 156 (2) |
C2—H2···N3ii | 0.98 (2) | 2.41 (2) | 3.3220 (19) | 154.6 (17) |
Symmetry codes: (i) −x+2, −y, −z; (ii) x, −y+1/2, z+1/2. |
The order–disorder (OD) theory was conceived in the 1950s (Dornberger-Schiff, 1956) to explain unusual X-ray diffraction effects in minerals like wollastonite (Jeffery, 1953) and in isostructural inorganic compounds such as Maddrell's salts and sodium polyarsenates (Dornberger-Schiff et al., 1955). It is based on the geometric equivalence of pairs of layers, which also implies energetic equivalence. Structures in which equivalent sides of a layer can connect to another layer only in a way where all resulting layer pairs are equivalent and fulfil the vicinity condition [Sentence incomplete - missing final clause? Please check] (Dornberger-Schiff & Grell-Niemann, 1961). A fundamental result of OD theory states that structures fulfilling the vicinity condition need not be equivalent or even ordered. If the vicinity condition gives rise to different stacking possibilities, one speaks of proper OD structures. These stacking possibilities are said to belong to the same OD family. Neglecting interactions of atoms distanced by more than one layer width, all polytypes of an OD family are energetically equivalent.
Since its inception, OD theory has been developed into a versatile theory for the explanation of polytypism, diffuse scattering, noncrystallographic extinctions and twinning, and as a means of classifying structures by symmetry principles. For example, all dense sphere packings can be considered to belong to the same OD family. OD theory has been successfully applied to all major classes of compounds. In the field of minerals and inorganic synthetic compounds, it has been very helpful in solving structural problems by suggesting reliable structural arrangements (Ferraris et al., 2004). It has also been applied, though less frequently, to organic salts and molecular compounds [e.g. urotropin azelate (Bonin et al., 2003), tris(bicyclo[2.1.1]hexeno)benzene (Birkedal et al., 2003; Ferraris et al., 2004) and nonactin (Dornberger-Schiff, 1966)], and recently even to proteins (Pletnev et al., 2009).
Since OD theory is based on geometric relations, it is not uncommon that OD layers do not correspond to layers in the crystallochemical sense. In this work, layers according to OD description will be designated by a letter A, according to the layer notation of Grell & Dornberger-Schiff (1982), whereas layers derived from crystallochemical considerations are denoted B.
During our systematic studies of a novel class of organic materials exhibiting nonlinear optical properties (Lumpi et al., 2011), we obtained crystals of the title compound, (I). Although they do not fulfill the basic requirements for second harmonic generation, since they crystallize in the centrosymmetric space group P21/c, they are interesting from a crystallographic point of view because they are systematically twinned and can be described as OD twins.
In crystals of (I), one crystallographically unique molecule (Fig. 1) is located on a general position. All interatomic distances are within the ranges of expected values (Allen et al., 2006). The phenyl and triazole rings are planar [maximum distances from the least-squares planes = 0.0045 (10) for atom C3 and 0.0042 (9) Å for atom C7]. They are tilted towards each other by 36.88 (6)°. This tilt is explained by repulsive steric forces between the 5- and ortho-H atoms of the triazole and phenyl rings. In comparable 4-alkyl-1-phenyl-1H-1,2,3-triazoles, which are not ortho-substituted on the phenyl ring, the tilt is generally less pronounced with angles <30°. For example, in the closely related propenyl analogue (Lumpi et al., 2011), the tilt angle is 8.87°. An exception is 2,6-bis[1-(4-dimethylaminophenyl)-1H-1,2,3-triazol-4-yl]-4-(3,6,9-trioxadeca-1-yloxycarbonyl)pyridine (Meudtner et al., 2007), exhibiting an exceptionally large tilt angle of 42.6°. Interestingly, the second 4-phenyl-1H-1,2,3-triazole moiety of the same molecule is close to planar (tilt angle = 0.7°). There are a number of such nearly planar 4-phenyl-1,2,3-triazoles, e.g. 2,6-bis[1-(4-dimethylaminophenyl)-1H-1,2,3-triazol-4-yl]-4-(3,6,9-trioxadeca-1-yloxycarbonyl)pyridine (Costa et al., 2006), with a tilt angle of 0.4°. Moreover, in 1-(4-methoxyphenyl)-4-(trifluoromethyl)triazole (Stepanova et al., 1989), the molecule is located on a mirror plane, thus resulting in planarity. A similar phenomenon has been observed and intensely investigated in the room-temperature phase of biphenyl (Trotter, 1961); the biphenyl molecule is located on a centre of inversion and is therefore planar. The preference for a flat geometry, despite the steric repulsive interaction of the ortho-H atoms, was explained by a π–π interaction between the connected aromatic rings and by intermolecular interactions (Cailleau et al., 1979).
The –CH═CH—S– group in (I) is nearly coplanar with the triazole ring [angle of the least-squares planes = 5.14 (13)°], whereas the S-methyl group is located distinctly off the molecular plane [torsion angle = 168.40 (15)°]. Only a few crystal structures of compounds with a similar methylsulfanylvinyl side chain are known. For all of them, similar torsion angles are observed: 171.2° in 2-(2-methylsulfonylprop-1-enyl)-4-methylsulfonylthiophene (Mereiter et al., 2000) and 159.6° in 5-methylsulfanyl-3-(morpholin-4-yl)hexa-2,4-dienenitrile (Mereiter et al., 2001).
The molecules of (I) are connected via nonclassical hydrogen bonds (Table 1). The phenyl rings are connected via C2—H2···N3 hydrogen bonds to the triazole rings, forming infinite chains running along [001]. These chains are, in turn, connected by C11—H113···N2 hydrogen bonds, forming crystallochemical layers B with symmetry P(1)21/c1 (Fig. 2). Adjacent layers B connect merely via van der Waals interactions between the phenyl rings. The shortest interlayer C—H contacts [C4—H4···C1 and C5—H5···C2, with H···C lengths of 2.93 (2) and 3.01 (2) Å, respectively] are too long for C—H···π interactions. Given a layer B, an adjacent layer can appear in two orientations, related by mirroring at (001). These two possibilities result in virtually identical inter- and intramolecular interactions, which explains the observed twinning and can be described by purely geometric considerations according to OD theory, as follows.
In order to achieve an OD description, the structure is `sliced' into OD layers with higher symmetry than required by the space-group symmetry. Accordingly, the structure of (I) is decomposed into two kinds of nonpolar (with respect to the stacking direction [100]) layers, viz. A1 (phenyl rings, without H2) and A2 (H2, triazole ring and aliphatic chain), which possess P(b)cm and P(1)21/c1 symmetry, respectively (Fig. 2).
The origins of two adjacent layers are related by a translation along 1/2a0±sc, where a0 is the vector normal to the layer planes connecting two equivalent layers, and s = -0.02 (determined from the lattice parameters of the twin mates). Thus, the OD family of the crystal structure of (I) belongs to category IV, characterized by the presence of two kinds of nonpolar OD layers. The OD groupoid family symbol according to the notation of Grell & Dornberger-Schiff (1982) reads as
A1 A2
P(b)cm P(1)21/c1
[0,s]
The number of stacking possibilities is formally derived using the NFZ relationship (Ďurovič, 1997). It is based on those layer symmetry operations which leave intact the orientation with respect to the stacking direction. For layers A1 these form the group P(2)cm. Since the mirror plane does not apply to layers A2, given the position of the former, the latter can appear in two orientations related by the mirror operation, which will be denoted A2+ and A2-. The twofold rotation generates the same pair of orientations and the c-glide applies to layers A2 as well and therefore does not produce additional possible orientations. For layers A2, on the other hand, the operations to be considered are the members of P(1)c1. All of them apply to adjacent layers A1. Thus, given the position of the former, the position of the latter is fixed. These stacking possibilities give rise to two polytypes with a maximum degree of order (MDO) (Dornberger-Schiff & Grell, 1982). For MDO1: P21/c, a = a0+2sc, all layers A2 appear in the same orientation. For MDO2: Pbca, a = 2a0, layers A2 appear alternately as A2+ and A2-.
A common feature in OD structures is desymmetrization of layers (Ďurovič, 1979). Indeed, the symmetry of layers A1 is reduced from P(b)cm to P(1)21/c1 and P(b)c21 in MDO1 and MDO2, respectively. The symmetry of layers A2, on the other hand, is retained in both MDO polytypes. The local and global symmetries of both MDO polytypes are shown schematically in Fig. 3.
As previously mentioned, crystals of (I) are twins. The twin mates are of the MDO1 polytype, appearing in two different orientations related by the mirror operation of layers A1. Polytype MDO2 is only evidenced indirectly by the twinning operation. At the contact plane, at least one layer triple A2+A1A2- of MDO2 exists.
In all polytypes the configuration and conformation of the molecules is identical and intermolecular interaction is confined to layers A2. The polytypes only differ in the relative orientation of molecules which are loosely connected by the phenyl rings. However, independent of the orientation, the arrangement of the phenyl rings is virtually identical, due to the higher symmetry of layers A1. Thus, the OD interpretation is valid and gives a plausible explanation of the observed twinning.