Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270103010655/ln1169sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270103010655/ln1169Isup2.hkl |
CCDC reference: 217144
The sample was prepared by Professor A. Vargvolis, University of Thessaloniki, Greece, and was recrystallized from ethyl acetate.
H atoms were located initially in difference maps. In the final refinement, their positions were determined by the HFIX instruction in SHELXL97 (Sheldrick, 1997) and they were then allowed to ride on their parent C atoms, with C—H = 0.95 Å and Uiso(H) = 1.2Ueq(C). The data set used in these calculations contains 3980 unique reflections when Friedel pairs are averaged.
Data collection: COLLECT (Nonius, 2000); cell refinement: HKL SCALEPACK (Otwinowski & Minor 1997); data reduction: DENZO and SCALEPACK (Otwinowski & Minor, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).
C18H15NO4S2 | F(000) = 776 |
Mr = 373.43 | Dx = 1.416 Mg m−3 |
Orthorhombic, Pca21 | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: P 2c -2ac | Cell parameters from 3666 reflections |
a = 8.9402 (2) Å | θ = 1.0–35.0° |
b = 17.2777 (5) Å | µ = 0.33 mm−1 |
c = 11.3437 (4) Å | T = 100 K |
V = 1752.22 (9) Å3 | Needle, yellow |
Z = 4 | 0.33 × 0.12 × 0.07 mm |
Bruker–Nonius KappaCCD diffractometer | 5207 reflections with I > 2σ(I) |
thick–slice ϕ scans | Rint = 0.061 |
Absorption correction: gaussian (Coppens et al., 1965) | θmax = 35.0°, θmin = 3.7° |
Tmin = 0.924, Tmax = 0.977 | h = 0→14 |
13541 measured reflections | k = −27→0 |
6736 independent reflections | l = −18→17 |
Refinement on F2 | H-atom parameters constrained |
Least-squares matrix: full | w = 1/[σ2(Fo2) + (0.0305P)2 + 1.561P] where P = (Fo2 + 2Fc2)/3 |
R[F2 > 2σ(F2)] = 0.056 | (Δ/σ)max < 0.001 |
wR(F2) = 0.116 | Δρmax = 0.45 e Å−3 |
S = 1.02 | Δρmin = −0.46 e Å−3 |
6736 reflections | Absolute structure: Flack & Bernardinelli, (2000); 2756 Friedel pairs |
226 parameters | Absolute structure parameter: −0.15 (7) |
1 restraint |
C18H15NO4S2 | V = 1752.22 (9) Å3 |
Mr = 373.43 | Z = 4 |
Orthorhombic, Pca21 | Mo Kα radiation |
a = 8.9402 (2) Å | µ = 0.33 mm−1 |
b = 17.2777 (5) Å | T = 100 K |
c = 11.3437 (4) Å | 0.33 × 0.12 × 0.07 mm |
Bruker–Nonius KappaCCD diffractometer | 6736 independent reflections |
Absorption correction: gaussian (Coppens et al., 1965) | 5207 reflections with I > 2σ(I) |
Tmin = 0.924, Tmax = 0.977 | Rint = 0.061 |
13541 measured reflections |
R[F2 > 2σ(F2)] = 0.056 | H-atom parameters constrained |
wR(F2) = 0.116 | Δρmax = 0.45 e Å−3 |
S = 1.02 | Δρmin = −0.46 e Å−3 |
6736 reflections | Absolute structure: Flack & Bernardinelli, (2000); 2756 Friedel pairs |
226 parameters | Absolute structure parameter: −0.15 (7) |
1 restraint |
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. |
x | y | z | Uiso*/Ueq | ||
S1 | 0.59299 (6) | 0.18345 (3) | 0.68268 (5) | 0.01505 (10) | |
S2 | 0.61196 (6) | 0.32860 (3) | 0.82693 (5) | 0.01561 (10) | |
O1 | 0.7022 (2) | 0.13850 (10) | 0.61757 (16) | 0.0222 (4) | |
O2 | 0.47125 (19) | 0.21676 (10) | 0.61553 (16) | 0.0203 (3) | |
O3 | 0.45636 (19) | 0.31041 (10) | 0.84803 (17) | 0.0207 (4) | |
O4 | 0.7055 (2) | 0.34871 (10) | 0.92688 (15) | 0.0212 (4) | |
N1 | 0.8510 (2) | 0.24646 (11) | 0.7548 (2) | 0.0151 (3) | |
C1 | 0.5054 (3) | 0.11925 (13) | 0.7833 (2) | 0.0176 (4) | |
C2 | 0.4084 (3) | 0.06413 (15) | 0.7361 (3) | 0.0278 (6) | |
H2 | 0.3889 | 0.0629 | 0.6538 | 0.033* | |
C3 | 0.3404 (4) | 0.01105 (16) | 0.8111 (3) | 0.0362 (7) | |
H3 | 0.275 | −0.0271 | 0.7796 | 0.043* | |
C4 | 0.3673 (4) | 0.01330 (16) | 0.9317 (3) | 0.0324 (7) | |
H4 | 0.3194 | −0.0228 | 0.9824 | 0.039* | |
C5 | 0.4638 (3) | 0.06810 (15) | 0.9780 (3) | 0.0275 (6) | |
H5 | 0.4824 | 0.0694 | 1.0604 | 0.033* | |
C6 | 0.5337 (3) | 0.12138 (14) | 0.9038 (2) | 0.0208 (5) | |
H6 | 0.6002 | 0.1589 | 0.9355 | 0.025* | |
C7 | 0.6178 (3) | 0.40977 (14) | 0.7306 (2) | 0.0196 (5) | |
C8 | 0.5503 (3) | 0.40518 (15) | 0.6214 (2) | 0.0251 (5) | |
H8 | 0.5052 | 0.3582 | 0.5962 | 0.03* | |
C9 | 0.5489 (4) | 0.46998 (17) | 0.5486 (3) | 0.0309 (6) | |
H9 | 0.502 | 0.4676 | 0.4735 | 0.037* | |
C10 | 0.6161 (4) | 0.53818 (16) | 0.5859 (3) | 0.0333 (7) | |
H10 | 0.6141 | 0.5825 | 0.5364 | 0.04* | |
C11 | 0.6861 (3) | 0.54205 (15) | 0.6950 (3) | 0.0332 (7) | |
H11 | 0.733 | 0.5887 | 0.7194 | 0.04* | |
C12 | 0.6878 (3) | 0.47758 (14) | 0.7687 (3) | 0.0273 (6) | |
H12 | 0.7356 | 0.4797 | 0.8434 | 0.033* | |
C13 | 0.6897 (2) | 0.25108 (14) | 0.7588 (2) | 0.0154 (4) | |
C14 | 0.9228 (3) | 0.26726 (13) | 0.6543 (2) | 0.0180 (5) | |
H14 | 0.8676 | 0.2874 | 0.5896 | 0.022* | |
C15 | 1.0756 (3) | 0.25929 (14) | 0.6458 (2) | 0.0219 (5) | |
H15 | 1.1257 | 0.2718 | 0.5745 | 0.026* | |
C16 | 1.1560 (3) | 0.23278 (16) | 0.7423 (3) | 0.0252 (5) | |
H16 | 1.2617 | 0.2282 | 0.7381 | 0.03* | |
C17 | 1.0811 (3) | 0.21314 (17) | 0.8442 (2) | 0.0268 (5) | |
H17 | 1.1352 | 0.1953 | 0.911 | 0.032* | |
C18 | 0.9274 (3) | 0.21949 (15) | 0.8490 (2) | 0.0217 (5) | |
H18 | 0.8753 | 0.2049 | 0.9186 | 0.026* |
U11 | U22 | U33 | U12 | U13 | U23 | |
S1 | 0.0138 (2) | 0.0183 (2) | 0.0131 (2) | −0.00146 (19) | 0.0009 (2) | −0.0016 (2) |
S2 | 0.0168 (2) | 0.0164 (2) | 0.0137 (2) | 0.00046 (19) | 0.0015 (2) | 0.0000 (2) |
O1 | 0.0194 (8) | 0.0233 (8) | 0.0239 (10) | −0.0009 (7) | 0.0057 (7) | −0.0078 (7) |
O2 | 0.0178 (8) | 0.0271 (8) | 0.0160 (8) | −0.0015 (7) | −0.0022 (7) | 0.0033 (7) |
O3 | 0.0152 (7) | 0.0241 (8) | 0.0227 (9) | 0.0009 (6) | 0.0039 (7) | −0.0015 (7) |
O4 | 0.0266 (9) | 0.0216 (8) | 0.0155 (8) | −0.0025 (7) | −0.0030 (7) | −0.0005 (7) |
N1 | 0.0136 (8) | 0.0169 (8) | 0.0148 (8) | −0.0009 (7) | −0.0011 (8) | 0.0004 (7) |
C1 | 0.0158 (10) | 0.0156 (9) | 0.0214 (11) | −0.0011 (8) | 0.0016 (9) | 0.0006 (8) |
C2 | 0.0295 (14) | 0.0260 (12) | 0.0280 (14) | −0.0119 (11) | −0.0033 (11) | −0.0001 (10) |
C3 | 0.0410 (17) | 0.0278 (13) | 0.0397 (19) | −0.0183 (12) | −0.0030 (14) | 0.0044 (13) |
C4 | 0.0342 (16) | 0.0282 (14) | 0.0347 (16) | −0.0093 (12) | 0.0027 (13) | 0.0109 (12) |
C5 | 0.0329 (15) | 0.0248 (12) | 0.0247 (13) | −0.0016 (11) | 0.0034 (11) | 0.0064 (11) |
C6 | 0.0224 (12) | 0.0200 (11) | 0.0201 (12) | −0.0014 (9) | 0.0007 (10) | −0.0007 (9) |
C7 | 0.0181 (11) | 0.0186 (10) | 0.0221 (12) | 0.0049 (9) | 0.0049 (9) | 0.0027 (9) |
C8 | 0.0322 (14) | 0.0232 (11) | 0.0200 (12) | 0.0044 (10) | −0.0022 (11) | 0.0018 (10) |
C9 | 0.0365 (16) | 0.0311 (14) | 0.0250 (14) | 0.0108 (12) | 0.0040 (12) | 0.0053 (11) |
C10 | 0.0378 (17) | 0.0256 (13) | 0.0366 (17) | 0.0086 (12) | 0.0095 (14) | 0.0127 (12) |
C11 | 0.0374 (15) | 0.0202 (11) | 0.0422 (18) | 0.0002 (11) | 0.0034 (14) | 0.0059 (12) |
C12 | 0.0283 (13) | 0.0209 (11) | 0.0326 (15) | −0.0004 (10) | −0.0012 (12) | 0.0033 (11) |
C13 | 0.0113 (8) | 0.0167 (9) | 0.0183 (10) | −0.0016 (8) | 0.0008 (9) | −0.0018 (8) |
C14 | 0.0180 (10) | 0.0208 (10) | 0.0152 (11) | −0.0035 (8) | 0.0027 (9) | 0.0034 (8) |
C15 | 0.0189 (11) | 0.0255 (11) | 0.0213 (12) | −0.0062 (9) | 0.0042 (9) | −0.0022 (9) |
C16 | 0.0152 (11) | 0.0340 (13) | 0.0264 (14) | 0.0010 (10) | −0.0002 (10) | −0.0047 (11) |
C17 | 0.0160 (11) | 0.0446 (15) | 0.0197 (13) | 0.0053 (10) | −0.0019 (10) | 0.0017 (11) |
C18 | 0.0182 (11) | 0.0313 (12) | 0.0157 (12) | 0.0026 (9) | 0.0001 (9) | 0.0030 (9) |
S1—O2 | 1.4477 (18) | C6—H6 | 0.95 |
S1—O1 | 1.4497 (18) | C7—C8 | 1.380 (4) |
S1—C13 | 1.691 (2) | C7—C12 | 1.397 (4) |
S1—C1 | 1.774 (2) | C8—C9 | 1.391 (4) |
S2—O3 | 1.4461 (18) | C8—H8 | 0.95 |
S2—O4 | 1.4510 (18) | C9—C10 | 1.389 (4) |
S2—C13 | 1.695 (2) | C9—H9 | 0.95 |
S2—C7 | 1.778 (2) | C10—C11 | 1.389 (4) |
N1—C18 | 1.352 (3) | C10—H10 | 0.95 |
N1—C14 | 1.357 (3) | C11—C12 | 1.393 (4) |
N1—C13 | 1.445 (3) | C11—H11 | 0.95 |
C1—C6 | 1.391 (4) | C12—H12 | 0.95 |
C1—C2 | 1.395 (3) | C14—C15 | 1.376 (3) |
C2—C3 | 1.391 (4) | C14—H14 | 0.95 |
C2—H2 | 0.95 | C15—C16 | 1.387 (4) |
C3—C4 | 1.389 (4) | C15—H15 | 0.95 |
C3—H3 | 0.95 | C16—C17 | 1.378 (4) |
C4—C5 | 1.384 (4) | C16—H16 | 0.95 |
C4—H4 | 0.95 | C17—C18 | 1.380 (4) |
C5—C6 | 1.395 (4) | C17—H17 | 0.95 |
C5—H5 | 0.95 | C18—H18 | 0.95 |
O2—S1—O1 | 116.82 (11) | C12—C7—S2 | 119.0 (2) |
O2—S1—C13 | 112.24 (11) | C7—C8—C9 | 119.4 (3) |
O1—S1—C13 | 106.62 (11) | C7—C8—H8 | 120.3 |
O2—S1—C1 | 104.79 (11) | C9—C8—H8 | 120.3 |
O1—S1—C1 | 106.86 (11) | C10—C9—C8 | 119.9 (3) |
C13—S1—C1 | 109.23 (13) | C10—C9—H9 | 120.1 |
O3—S2—O4 | 118.49 (11) | C8—C9—H9 | 120.1 |
O3—S2—C13 | 107.35 (10) | C11—C10—C9 | 120.5 (3) |
O4—S2—C13 | 108.01 (12) | C11—C10—H10 | 119.8 |
O3—S2—C7 | 107.54 (11) | C9—C10—H10 | 119.8 |
O4—S2—C7 | 105.91 (11) | C10—C11—C12 | 120.1 (3) |
C13—S2—C7 | 109.32 (12) | C10—C11—H11 | 120 |
C18—N1—C14 | 121.09 (19) | C12—C11—H11 | 120 |
C18—N1—C13 | 119.9 (2) | C11—C12—C7 | 118.7 (3) |
C14—N1—C13 | 119.0 (2) | C11—C12—H12 | 120.6 |
C6—C1—C2 | 120.6 (2) | C7—C12—H12 | 120.6 |
C6—C1—S1 | 122.40 (19) | N1—C13—S1 | 117.13 (18) |
C2—C1—S1 | 117.0 (2) | N1—C13—S2 | 117.85 (17) |
C3—C2—C1 | 119.1 (3) | S1—C13—S2 | 124.69 (13) |
C3—C2—H2 | 120.4 | N1—C14—C15 | 120.1 (2) |
C1—C2—H2 | 120.4 | N1—C14—H14 | 119.9 |
C4—C3—C2 | 120.5 (3) | C15—C14—H14 | 119.9 |
C4—C3—H3 | 119.7 | C14—C15—C16 | 119.5 (2) |
C2—C3—H3 | 119.7 | C14—C15—H15 | 120.3 |
C5—C4—C3 | 120.0 (3) | C16—C15—H15 | 120.3 |
C5—C4—H4 | 120 | C17—C16—C15 | 119.4 (2) |
C3—C4—H4 | 120 | C17—C16—H16 | 120.3 |
C4—C5—C6 | 120.1 (3) | C15—C16—H16 | 120.3 |
C4—C5—H5 | 119.9 | C16—C17—C18 | 119.8 (2) |
C6—C5—H5 | 119.9 | C16—C17—H17 | 120.1 |
C1—C6—C5 | 119.6 (2) | C18—C17—H17 | 120.1 |
C1—C6—H6 | 120.2 | N1—C18—C17 | 120.0 (2) |
C5—C6—H6 | 120.2 | N1—C18—H18 | 120 |
C8—C7—C12 | 121.4 (2) | C17—C18—H18 | 120 |
C8—C7—S2 | 119.5 (2) | ||
O2—S1—C1—C6 | −128.3 (2) | C8—C7—C12—C11 | 1.3 (4) |
O1—S1—C1—C6 | 107.1 (2) | S2—C7—C12—C11 | −177.1 (2) |
C13—S1—C1—C6 | −7.9 (3) | C18—N1—C13—S1 | −104.8 (3) |
O2—S1—C1—C2 | 53.3 (2) | C14—N1—C13—S1 | 73.2 (3) |
O1—S1—C1—C2 | −71.2 (2) | C18—N1—C13—S2 | 81.4 (3) |
C13—S1—C1—C2 | 173.8 (2) | C14—N1—C13—S2 | −100.5 (2) |
C6—C1—C2—C3 | −0.2 (4) | O2—S1—C13—N1 | −135.06 (19) |
S1—C1—C2—C3 | 178.1 (2) | O1—S1—C13—N1 | −6.0 (2) |
C1—C2—C3—C4 | 0.7 (5) | C1—S1—C13—N1 | 109.2 (2) |
C2—C3—C4—C5 | −0.8 (5) | O2—S1—C13—S2 | 38.2 (2) |
C3—C4—C5—C6 | 0.3 (5) | O1—S1—C13—S2 | 167.34 (17) |
C2—C1—C6—C5 | −0.3 (4) | C1—S1—C13—S2 | −77.5 (2) |
S1—C1—C6—C5 | −178.5 (2) | O3—S2—C13—N1 | −164.67 (19) |
C4—C5—C6—C1 | 0.2 (4) | O4—S2—C13—N1 | −35.8 (2) |
O3—S2—C7—C8 | −58.5 (2) | C7—S2—C13—N1 | 79.0 (2) |
O4—S2—C7—C8 | 173.9 (2) | O3—S2—C13—S1 | 22.1 (2) |
C13—S2—C7—C8 | 57.7 (2) | O4—S2—C13—S1 | 150.91 (17) |
O3—S2—C7—C12 | 119.9 (2) | C7—S2—C13—S1 | −94.3 (2) |
O4—S2—C7—C12 | −7.7 (2) | C18—N1—C14—C15 | 1.6 (4) |
C13—S2—C7—C12 | −123.8 (2) | C13—N1—C14—C15 | −176.3 (2) |
C12—C7—C8—C9 | −1.4 (4) | N1—C14—C15—C16 | −2.5 (4) |
S2—C7—C8—C9 | 176.9 (2) | C14—C15—C16—C17 | 1.5 (4) |
C7—C8—C9—C10 | 0.5 (4) | C15—C16—C17—C18 | 0.5 (4) |
C8—C9—C10—C11 | 0.6 (5) | C14—N1—C18—C17 | 0.3 (4) |
C9—C10—C11—C12 | −0.8 (5) | C13—N1—C18—C17 | 178.3 (2) |
C10—C11—C12—C7 | −0.1 (4) | C16—C17—C18—N1 | −1.4 (4) |
Experimental details
Crystal data | |
Chemical formula | C18H15NO4S2 |
Mr | 373.43 |
Crystal system, space group | Orthorhombic, Pca21 |
Temperature (K) | 100 |
a, b, c (Å) | 8.9402 (2), 17.2777 (5), 11.3437 (4) |
V (Å3) | 1752.22 (9) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.33 |
Crystal size (mm) | 0.33 × 0.12 × 0.07 |
Data collection | |
Diffractometer | Bruker–Nonius KappaCCD diffractometer |
Absorption correction | Gaussian (Coppens et al., 1965) |
Tmin, Tmax | 0.924, 0.977 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 13541, 6736, 5207 |
Rint | 0.061 |
(sin θ/λ)max (Å−1) | 0.807 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.056, 0.116, 1.02 |
No. of reflections | 6736 |
No. of parameters | 226 |
No. of restraints | 1 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.45, −0.46 |
Absolute structure | Flack & Bernardinelli, (2000); 2756 Friedel pairs |
Absolute structure parameter | −0.15 (7) |
Computer programs: COLLECT (Nonius, 2000), HKL SCALEPACK (Otwinowski & Minor 1997), DENZO and SCALEPACK (Otwinowski & Minor, 1997), SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), ORTEP-3 for Windows (Farrugia, 1997), WinGX (Farrugia, 1999).
S1—C13 | 1.691 (2) | N1—C18 | 1.352 (3) |
S1—C1 | 1.774 (2) | N1—C14 | 1.357 (3) |
S2—C13 | 1.695 (2) | N1—C13 | 1.445 (3) |
S2—C7 | 1.778 (2) | ||
N1—C13—S1 | 117.13 (18) | S1—C13—S2 | 124.69 (13) |
N1—C13—S2 | 117.85 (17) | ||
C13—S1—C1—C6 | −7.9 (3) | O1—S1—C13—N1 | −6.0 (2) |
C13—S2—C7—C8 | 57.7 (2) | O4—S2—C13—N1 | −35.8 (2) |
C14—N1—C13—S1 | 73.2 (3) |
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The title compound, (I), provides the first structural example of a pyridinium ylide in which the negative charge on the ylide C atom is stabilized by electron-withdrawing sulfonyl groups.
In (I), ylide atom C13 is bonded to the pyridinium N atom and to two S atoms; it lies only 0.053 (2) Å from the NS2 plane (Fig. 1). The bond lengths and the molecular conformation indicate that C13—N1 is essentially a single bond and that the negative charge formally associated with atom C13 is substantially delocalized to atoms S1 and S2. Thus, significant pπ–pπ overlap across N1—C13 is precluded by the near orthogonality of the relevant p-orbitals of atoms N1 and C13 [the C14—N1—C13—S1 torsion angle is 73.2 (3)°]. Consistent with this, the N1—C13 distance is 0.09 Å longer than the aromatic N1—Cpy bond lengths; indeed, the N1—C13 bond length of 1.445 (3) Å is substantially longer than any mean value for an Csp2—N3 bond in the compilation of Orpen et al. (1992). The C13—S bonds are, on average, 0.08 Å shorter than the S—CPh distances, signalling the transfer of charge from atom C13 to the S atoms. This conclusion is consistent with hydrogen-bond basicity and IR spectroscopic studies on sulfonyl-stabilized nitrogen ylides: these have shown that sulfonamidates, –SO2N(-)N(+)Me3, are amongst the strongest sulfonyl bases known as a result of electron release from the negatively charged N atom to the sulfonyl group. The mechanism of this electron release is thought to be mainly inductive (see Chardin et al., 1996, and references therein).
The closest comparison to (I) among known structures is provided by the acridinium ylide, (II) (Ning et al., 1976), in which a chlorosulfinyl substituent is one of the two stabilizing groups. The S—C(ylide) distance in (II) of 1.668 (8) Å is only slightly shorter than the corresponding distances in (I), while the N—Cylide distance (1.447 Å) is nearly identical with that in (I).
A search of the Cambridge Structural Database (Allen, 2002; in the subsequent discussion geometric parameters not given explicitly in the primary source have been recalculated using the program QUEST) reveals that in the other pyridinium ylides, (IIIa)–(IIIe) (see Scheme), which have been characterized by diffraction methods, the ylide C atom participates in two C—C bonds. In these structures, the bonds radiating from the ylide C atom are nearly coplanar, the pyridinium (py) and ylide planes are roughly normal to one another (Cpy—N—Cylide—C torsion angles 61–84°), the N—Cylide distances (1.454–1.474 Å) are on average slightly longer than the corresponding values in (I) and (II), and the C—Cylide—C bond angles (127.4–129.6°) are all much larger than 120°. This last feature may have a steric origin: the corresponding angles in (I) [124.7 (1)°] and (II) [123.3 (1)°] deviate less from 120°.
Finally, we note that the structures of 1,1-dicyano-1-pyridiniomethanide compounds differ from those of (I)–(III) in that the angle between the C(CN)2 and pyridinium planes is close to zero, permitting conjugation across the N—C(ylide) bonds. These, in consequence, are shorter (1.416–1.427 Å) than those in (I)–(III) (see, for example, Matsumoto et al., 1998; Baert et al., 1982). The angles at the ylide C atom in these dicyano compounds do not show the large deviations from 120° typical of (III).