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The title
p-haloacetophenones, C
8H
7XO (
X = Cl, Br and I), have different packing modes. The chloro compound contains H
O and H
Cl contacts, but no Cl
O contacts. The bromo compound and one polymorph (
A) of the iodo compound are isomorphous, with significant
XO contacts [Br
O = 3.320 (4) Å and I
O = 3.374 (5) Å]. In the other polymorph (
B) of the iodo compound, the I
O distance is 3.082 (4) Å. Both polymorphs contain C-H
contacts; these contacts are shorter in
A than in
B.
Supporting information
CCDC references: 248149; 248150; 248151; 248152
For each of the four structures a complete sphere of data was collected and all possible Friedel pairs were measured. For ClM, 638 (62%) of the 1036 pairs contained information about which enantiomer was present; refinement as a racemic twin led to a minor twin fraction of 0.11 (8). For BrM [827 (96%) of 864 pairs], the refinement converged with a Flack (1983) parameter of −0.004 (14), and for IM—A [897 (97%) of 924 pairs], the refinement converged with a Flack parameter of −0.01 (13), indicating that the reported polarities are correct. In the refinement of BrM and IM—A, the origin restraints on x and z were made using the method of Flack & Schwarzenbach (1988). After the refinements were complete, the origin was shifted, in each case, to x = 0.5 and z = 1/2, to facilitate comparison between the two structures. In the final refinement of each of the four structures, the methyl H atoms were included with idealized distances and angles, since this treatment seems appropriate in the presence of the heavy atoms. However, in each case, the H atoms were also found from a difference Fourier map and the positions and Uiso values were refined; these results agreed with the group refinements within experimental error in every case.
For all compounds, data collection: SMART (Siemens, 1995); cell refinement: SAINT (Siemens, 1995); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 1997); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.
(ClM) 4-chloroacetophenone
top
Crystal data top
C8H7ClO | F(000) = 320 |
Mr = 154.59 | Dx = 1.382 Mg m−3 |
Orthorhombic, P212121 | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: P 2ac 2ab | Cell parameters from 1949 reflections |
a = 4.0079 (10) Å | θ = 2.4–25.6° |
b = 9.366 (2) Å | µ = 0.44 mm−1 |
c = 19.787 (5) Å | T = 173 K |
V = 742.8 (3) Å3 | Irregular prism, colorless |
Z = 4 | 0.50 × 0.40 × 0.30 mm |
Data collection top
Siemens SMART area-detector diffractometer | 1674 independent reflections |
Radiation source: fine-focus sealed tube | 1434 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.039 |
ω scans | θmax = 27.5°, θmin = 2.1° |
Absorption correction: multi-scan SADABS; Sheldrick, 1996; Blessing, 1995 | h = −5→5 |
Tmin = 0.81, Tmax = 0.88 | k = −12→11 |
6382 measured reflections | l = −25→23 |
Refinement top
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.034 | H-atom parameters constrained |
wR(F2) = 0.080 | w = 1/[σ2(Fo2) + (0.037P)2 + 0.061P] where
P = (Fo2 + 2Fc2)/3 |
S = 1.03 | (Δ/σ)max = 0.002 |
1674 reflections | Δρmax = 0.17 e Å−3 |
91 parameters | Δρmin = −0.14 e Å−3 |
0 restraints | Absolute structure: Flack (1983) |
Primary atom site location: structure-invariant direct methods | Absolute structure parameter: 0.11 (8) |
Crystal data top
C8H7ClO | V = 742.8 (3) Å3 |
Mr = 154.59 | Z = 4 |
Orthorhombic, P212121 | Mo Kα radiation |
a = 4.0079 (10) Å | µ = 0.44 mm−1 |
b = 9.366 (2) Å | T = 173 K |
c = 19.787 (5) Å | 0.50 × 0.40 × 0.30 mm |
Data collection top
Siemens SMART area-detector diffractometer | 1674 independent reflections |
Absorption correction: multi-scan SADABS; Sheldrick, 1996; Blessing, 1995 | 1434 reflections with I > 2σ(I) |
Tmin = 0.81, Tmax = 0.88 | Rint = 0.039 |
6382 measured reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.034 | H-atom parameters constrained |
wR(F2) = 0.080 | Δρmax = 0.17 e Å−3 |
S = 1.03 | Δρmin = −0.14 e Å−3 |
1674 reflections | Absolute structure: Flack (1983) |
91 parameters | Absolute structure parameter: 0.11 (8) |
0 restraints | |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | |
Cl1 | 0.66962 (14) | 0.52846 (6) | 0.44469 (3) | 0.04525 (17) | |
O1 | 0.1053 (4) | 0.36413 (15) | 0.75213 (8) | 0.0476 (4) | |
C1 | 0.3741 (4) | 0.48590 (19) | 0.66333 (9) | 0.0287 (4) | |
C2 | 0.2919 (5) | 0.38008 (18) | 0.61662 (9) | 0.0318 (4) | |
H2 | 0.1741 | 0.2976 | 0.6312 | 0.038* | |
C3 | 0.3790 (5) | 0.39346 (19) | 0.54971 (10) | 0.0337 (4) | |
H3 | 0.3205 | 0.3213 | 0.5181 | 0.040* | |
C4 | 0.5526 (4) | 0.5132 (2) | 0.52905 (10) | 0.0311 (4) | |
C5 | 0.6366 (5) | 0.62079 (19) | 0.57378 (10) | 0.0349 (4) | |
H5 | 0.7531 | 0.7032 | 0.5587 | 0.042* | |
C6 | 0.5475 (5) | 0.60607 (19) | 0.64111 (10) | 0.0325 (4) | |
H6 | 0.6052 | 0.6788 | 0.6725 | 0.039* | |
C7 | 0.2738 (4) | 0.4665 (2) | 0.73563 (9) | 0.0320 (4) | |
C8 | 0.3818 (5) | 0.5757 (2) | 0.78664 (10) | 0.0414 (5) | |
H8A | 0.2998 | 0.5482 | 0.8315 | 0.062* | |
H8B | 0.2901 | 0.6691 | 0.7743 | 0.062* | |
H8C | 0.6259 | 0.5810 | 0.7874 | 0.062* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Cl1 | 0.0507 (3) | 0.0523 (3) | 0.0327 (3) | 0.0026 (2) | 0.0045 (2) | −0.0016 (2) |
O1 | 0.0578 (10) | 0.0389 (8) | 0.0461 (9) | −0.0046 (8) | 0.0061 (8) | 0.0089 (7) |
C1 | 0.0246 (9) | 0.0271 (9) | 0.0344 (10) | 0.0047 (7) | −0.0040 (7) | −0.0006 (7) |
C2 | 0.0319 (9) | 0.0229 (9) | 0.0405 (11) | −0.0010 (7) | −0.0016 (9) | −0.0006 (8) |
C3 | 0.0331 (10) | 0.0307 (9) | 0.0373 (11) | 0.0028 (8) | −0.0044 (9) | −0.0073 (8) |
C4 | 0.0290 (8) | 0.0335 (10) | 0.0309 (9) | 0.0058 (8) | −0.0013 (7) | −0.0017 (8) |
C5 | 0.0378 (11) | 0.0279 (9) | 0.0390 (11) | −0.0016 (9) | −0.0003 (9) | 0.0009 (8) |
C6 | 0.0356 (10) | 0.0247 (9) | 0.0371 (11) | 0.0009 (8) | −0.0032 (8) | −0.0039 (8) |
C7 | 0.0298 (9) | 0.0322 (9) | 0.0340 (10) | 0.0074 (9) | −0.0021 (7) | 0.0041 (8) |
C8 | 0.0401 (12) | 0.0528 (12) | 0.0312 (10) | 0.0041 (10) | 0.0001 (9) | −0.0051 (9) |
Geometric parameters (Å, º) top
Cl1—C4 | 1.740 (2) | C4—C5 | 1.383 (3) |
O1—C7 | 1.217 (2) | C5—C6 | 1.386 (3) |
C1—C6 | 1.394 (3) | C5—H5 | 0.9500 |
C1—C2 | 1.395 (3) | C6—H6 | 0.9500 |
C1—C7 | 1.497 (3) | C7—C8 | 1.500 (3) |
C2—C3 | 1.375 (3) | C8—H8A | 0.9800 |
C2—H2 | 0.9500 | C8—H8B | 0.9800 |
C3—C4 | 1.382 (3) | C8—H8C | 0.9800 |
C3—H3 | 0.9500 | | |
| | | |
C6—C1—C2 | 118.86 (17) | C6—C5—H5 | 120.7 |
C6—C1—C7 | 122.22 (17) | C5—C6—C1 | 120.79 (17) |
C2—C1—C7 | 118.93 (16) | C5—C6—H6 | 119.6 |
C3—C2—C1 | 120.89 (17) | C1—C6—H6 | 119.6 |
C3—C2—H2 | 119.6 | O1—C7—C1 | 120.05 (17) |
C1—C2—H2 | 119.6 | O1—C7—C8 | 121.07 (18) |
C2—C3—C4 | 119.13 (17) | C1—C7—C8 | 118.87 (17) |
C2—C3—H3 | 120.4 | C7—C8—H8A | 109.5 |
C4—C3—H3 | 120.4 | C7—C8—H8B | 109.5 |
C3—C4—C5 | 121.65 (18) | H8A—C8—H8B | 109.5 |
C3—C4—Cl1 | 119.12 (15) | C7—C8—H8C | 109.5 |
C5—C4—Cl1 | 119.24 (15) | H8A—C8—H8C | 109.5 |
C4—C5—C6 | 118.67 (17) | H8B—C8—H8C | 109.5 |
C4—C5—H5 | 120.7 | | |
(BrM) 4-bromoacetophenone
top
Crystal data top
C8H7BrO | F(000) = 392 |
Mr = 199.05 | Dx = 1.739 Mg m−3 |
Monoclinic, Cc | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: C -2yc | Cell parameters from 2078 reflections |
a = 18.635 (5) Å | θ = 2.2–25.7° |
b = 6.9554 (17) Å | µ = 5.33 mm−1 |
c = 5.9035 (15) Å | T = 173 K |
β = 96.36 (1)° | Plate, colorless |
V = 760.5 (3) Å3 | 0.45 × 0.15 × 0.03 mm |
Z = 4 | |
Data collection top
Siemens SMART area-detector diffractometer | 1691 independent reflections |
Radiation source: fine-focus sealed tube | 1569 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.038 |
ω scans | θmax = 27.5°, θmin = 3.1° |
Absorption correction: multi-scan (SADABS including thin plate correction; Sheldrick, 1996; Blessing,
1995) | h = −23→23 |
Tmin = 0.39, Tmax = 0.85 | k = −8→9 |
3840 measured reflections | l = −7→7 |
Refinement top
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.032 | H-atom parameters constrained |
wR(F2) = 0.077 | w = 1/[σ2(Fo2) + (0.036P)2] where
P = (Fo2 + 2Fc2)/3 |
S = 1.05 | (Δ/σ)max = 0.001 |
1691 reflections | Δρmax = 0.75 e Å−3 |
91 parameters | Δρmin = −0.27 e Å−3 |
2 restraints | Absolute structure: Flack(1983),
849 Friedel pairs |
Primary atom site location: structure-invariant direct methods | Absolute structure parameter: −0.004 (14) |
Crystal data top
C8H7BrO | V = 760.5 (3) Å3 |
Mr = 199.05 | Z = 4 |
Monoclinic, Cc | Mo Kα radiation |
a = 18.635 (5) Å | µ = 5.33 mm−1 |
b = 6.9554 (17) Å | T = 173 K |
c = 5.9035 (15) Å | 0.45 × 0.15 × 0.03 mm |
β = 96.36 (1)° | |
Data collection top
Siemens SMART area-detector diffractometer | 1691 independent reflections |
Absorption correction: multi-scan (SADABS including thin plate correction; Sheldrick, 1996; Blessing,
1995) | 1569 reflections with I > 2σ(I) |
Tmin = 0.39, Tmax = 0.85 | Rint = 0.038 |
3840 measured reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.032 | H-atom parameters constrained |
wR(F2) = 0.077 | Δρmax = 0.75 e Å−3 |
S = 1.05 | Δρmin = −0.27 e Å−3 |
1691 reflections | Absolute structure: Flack(1983),
849 Friedel pairs |
91 parameters | Absolute structure parameter: −0.004 (14) |
2 restraints | |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | |
Br1 | 0.5000 | 0.27942 (5) | 0.5000 | 0.04028 (13) | |
O1 | 0.8276 (2) | 0.1930 (5) | 0.0907 (6) | 0.0486 (8) | |
C1 | 0.7401 (2) | 0.2382 (4) | 0.3424 (7) | 0.0266 (7) | |
C2 | 0.6834 (2) | 0.1785 (6) | 0.1811 (7) | 0.0284 (9) | |
H2 | 0.6941 | 0.1297 | 0.0384 | 0.034* | |
C3 | 0.6124 (2) | 0.1895 (5) | 0.2261 (6) | 0.0292 (8) | |
H3 | 0.5746 | 0.1480 | 0.1157 | 0.035* | |
C4 | 0.5969 (2) | 0.2617 (5) | 0.4340 (7) | 0.0282 (8) | |
C5 | 0.6516 (2) | 0.3221 (5) | 0.5979 (6) | 0.0271 (7) | |
H5 | 0.6402 | 0.3728 | 0.7390 | 0.033* | |
C6 | 0.7226 (2) | 0.3078 (5) | 0.5534 (6) | 0.0282 (8) | |
H6 | 0.7602 | 0.3454 | 0.6668 | 0.034* | |
C7 | 0.8153 (3) | 0.2291 (7) | 0.2851 (8) | 0.0341 (9) | |
C8 | 0.8756 (3) | 0.2688 (6) | 0.4701 (9) | 0.0439 (10) | |
H8A | 0.9221 | 0.2574 | 0.4079 | 0.066* | |
H8B | 0.8737 | 0.1757 | 0.5938 | 0.066* | |
H8C | 0.8705 | 0.3992 | 0.5291 | 0.066* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Br1 | 0.03165 (19) | 0.0465 (2) | 0.0438 (2) | 0.0034 (4) | 0.00901 (13) | 0.0015 (5) |
O1 | 0.0398 (19) | 0.071 (2) | 0.0368 (16) | −0.0005 (16) | 0.0133 (14) | −0.0054 (14) |
C1 | 0.036 (2) | 0.0173 (16) | 0.0269 (16) | −0.0001 (12) | 0.0042 (15) | 0.0007 (12) |
C2 | 0.040 (2) | 0.023 (2) | 0.0228 (18) | 0.0000 (17) | 0.0047 (14) | 0.0003 (15) |
C3 | 0.035 (2) | 0.026 (2) | 0.0261 (17) | −0.0029 (14) | −0.0015 (14) | −0.0036 (12) |
C4 | 0.0271 (19) | 0.0241 (18) | 0.0342 (19) | 0.0020 (13) | 0.0074 (15) | 0.0050 (13) |
C5 | 0.037 (2) | 0.0214 (18) | 0.0234 (16) | 0.0033 (13) | 0.0041 (14) | −0.0021 (12) |
C6 | 0.037 (2) | 0.0221 (19) | 0.0257 (18) | −0.0018 (13) | 0.0031 (15) | −0.0010 (12) |
C7 | 0.038 (2) | 0.030 (2) | 0.035 (2) | 0.002 (2) | 0.0076 (18) | 0.0011 (19) |
C8 | 0.031 (2) | 0.056 (3) | 0.046 (3) | −0.0022 (18) | 0.0067 (19) | −0.0032 (18) |
Geometric parameters (Å, º) top
Br1—C4 | 1.892 (4) | C4—C5 | 1.390 (6) |
O1—C7 | 1.221 (6) | C5—C6 | 1.382 (5) |
C1—C2 | 1.405 (6) | C5—H5 | 0.9500 |
C1—C6 | 1.408 (5) | C6—H6 | 0.9500 |
C1—C7 | 1.478 (7) | C7—C8 | 1.504 (7) |
C2—C3 | 1.379 (6) | C8—H8A | 0.9800 |
C2—H2 | 0.9500 | C8—H8B | 0.9800 |
C3—C4 | 1.386 (6) | C8—H8C | 0.9800 |
C3—H3 | 0.9500 | | |
| | | |
C2—C1—C6 | 118.1 (4) | C4—C5—H5 | 120.3 |
C2—C1—C7 | 119.6 (4) | C5—C6—C1 | 120.9 (4) |
C6—C1—C7 | 122.4 (4) | C5—C6—H6 | 119.5 |
C3—C2—C1 | 121.3 (4) | C1—C6—H6 | 119.5 |
C3—C2—H2 | 119.4 | O1—C7—C1 | 120.4 (4) |
C1—C2—H2 | 119.4 | O1—C7—C8 | 121.1 (5) |
C4—C3—C2 | 119.3 (4) | C1—C7—C8 | 118.5 (4) |
C4—C3—H3 | 120.3 | C7—C8—H8A | 109.5 |
C2—C3—H3 | 120.3 | C7—C8—H8B | 109.5 |
C3—C4—C5 | 121.1 (4) | H8A—C8—H8B | 109.5 |
C3—C4—Br1 | 120.3 (3) | C7—C8—H8C | 109.5 |
C5—C4—Br1 | 118.7 (3) | H8A—C8—H8C | 109.5 |
C6—C5—C4 | 119.4 (3) | H8B—C8—H8C | 109.5 |
C6—C5—H5 | 120.3 | | |
(IM-A)
p-iodoacetophenone polymorph A
top
Crystal data top
C8H7IO | F(000) = 464 |
Mr = 246.04 | Dx = 2.037 Mg m−3 |
Monoclinic, Cc | Melting point: 358-359 K K |
Hall symbol: C -2yc | Mo Kα radiation, λ = 0.71073 Å |
a = 19.425 (5) Å | Cell parameters from 3302 reflections |
b = 7.049 (2) Å | θ = 3.1–27.5° |
c = 5.8769 (15) Å | µ = 3.92 mm−1 |
β = 94.41 (1)° | T = 173 K |
V = 802.3 (4) Å3 | Plate, pale yellow |
Z = 4 | 0.25 × 0.20 × 0.10 mm |
Data collection top
Siemens SMART area-detector diffractometer | 1821 independent reflections |
Radiation source: fine-focus sealed tube | 1768 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.031 |
ω scans | θmax = 27.5°, θmin = 2.1° |
Absorption correction: multi-scan (SADABS; Sheldrick, 1996; Blessing, 1995) | h = −25→25 |
Tmin = 0.38, Tmax = 0.68 | k = −9→9 |
4483 measured reflections | l = −7→7 |
Refinement top
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.023 | H-atom parameters constrained |
wR(F2) = 0.060 | w = 1/[σ2(Fo2) + (0.032P)2 + 0.031P] where
P = (Fo2 + 2Fc2)/3 |
S = 1.05 | (Δ/σ)max = 0.001 |
1821 reflections | Δρmax = 0.63 e Å−3 |
91 parameters | Δρmin = −0.31 e Å−3 |
2 restraints | Absolute structure: Flack (1983) |
Primary atom site location: structure-invariant direct methods | Absolute structure parameter: −0.01 (3) |
Crystal data top
C8H7IO | V = 802.3 (4) Å3 |
Mr = 246.04 | Z = 4 |
Monoclinic, Cc | Mo Kα radiation |
a = 19.425 (5) Å | µ = 3.92 mm−1 |
b = 7.049 (2) Å | T = 173 K |
c = 5.8769 (15) Å | 0.25 × 0.20 × 0.10 mm |
β = 94.41 (1)° | |
Data collection top
Siemens SMART area-detector diffractometer | 1821 independent reflections |
Absorption correction: multi-scan (SADABS; Sheldrick, 1996; Blessing, 1995) | 1768 reflections with I > 2σ(I) |
Tmin = 0.38, Tmax = 0.68 | Rint = 0.031 |
4483 measured reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.023 | H-atom parameters constrained |
wR(F2) = 0.060 | Δρmax = 0.63 e Å−3 |
S = 1.05 | Δρmin = −0.31 e Å−3 |
1821 reflections | Absolute structure: Flack (1983) |
91 parameters | Absolute structure parameter: −0.01 (3) |
2 restraints | |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | |
I1 | 0.5000 | 0.26811 (3) | 0.5000 | 0.03998 (9) | |
O1 | 0.8311 (2) | 0.2031 (5) | 0.0940 (7) | 0.0532 (8) | |
C1 | 0.7426 (2) | 0.2402 (4) | 0.3415 (7) | 0.0278 (7) | |
C2 | 0.6910 (2) | 0.1829 (6) | 0.1788 (7) | 0.0297 (8) | |
H2 | 0.7034 | 0.1383 | 0.0351 | 0.036* | |
C3 | 0.6220 (2) | 0.1895 (5) | 0.2210 (6) | 0.0307 (6) | |
H3 | 0.5876 | 0.1475 | 0.1088 | 0.037* | |
C4 | 0.6037 (2) | 0.2580 (4) | 0.4291 (7) | 0.0285 (8) | |
C5 | 0.6537 (2) | 0.3188 (5) | 0.5961 (6) | 0.0300 (6) | |
H5 | 0.6405 | 0.3664 | 0.7376 | 0.036* | |
C6 | 0.7228 (2) | 0.3088 (5) | 0.5534 (6) | 0.0303 (6) | |
H6 | 0.7572 | 0.3484 | 0.6673 | 0.036* | |
C7 | 0.8164 (3) | 0.2347 (6) | 0.2888 (9) | 0.0337 (9) | |
C8 | 0.8714 (3) | 0.2684 (6) | 0.4777 (10) | 0.0475 (11) | |
H8A | 0.9169 | 0.2613 | 0.4169 | 0.071* | |
H8B | 0.8681 | 0.1716 | 0.5960 | 0.071* | |
H8C | 0.8651 | 0.3944 | 0.5436 | 0.071* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
I1 | 0.03069 (13) | 0.04697 (13) | 0.04280 (14) | 0.0027 (3) | 0.00627 (9) | 0.0040 (3) |
O1 | 0.0398 (19) | 0.083 (2) | 0.0382 (16) | −0.0006 (17) | 0.0135 (14) | −0.0091 (16) |
C1 | 0.032 (2) | 0.0273 (15) | 0.0250 (16) | 0.0004 (11) | 0.0064 (14) | 0.0007 (10) |
C2 | 0.0402 (19) | 0.0263 (18) | 0.0228 (16) | 0.0007 (16) | 0.0034 (13) | −0.0010 (14) |
C3 | 0.0349 (18) | 0.0292 (15) | 0.0272 (15) | −0.0011 (14) | −0.0025 (13) | −0.0034 (12) |
C4 | 0.030 (2) | 0.0259 (15) | 0.0300 (19) | 0.0006 (11) | 0.0023 (16) | 0.0040 (10) |
C5 | 0.0403 (18) | 0.0267 (14) | 0.0230 (14) | 0.0008 (13) | 0.0030 (12) | −0.0007 (11) |
C6 | 0.0367 (17) | 0.0278 (15) | 0.0261 (15) | −0.0025 (13) | 0.0013 (12) | −0.0033 (12) |
C7 | 0.034 (2) | 0.029 (2) | 0.038 (2) | 0.0011 (16) | 0.0074 (18) | 0.0002 (15) |
C8 | 0.033 (2) | 0.068 (3) | 0.042 (3) | −0.0055 (17) | 0.0051 (19) | −0.0008 (17) |
Geometric parameters (Å, º) top
I1—C4 | 2.090 (5) | C4—C5 | 1.393 (6) |
O1—C7 | 1.221 (7) | C5—C6 | 1.387 (5) |
C1—C2 | 1.391 (6) | C5—H5 | 0.9500 |
C1—C6 | 1.416 (5) | C6—H6 | 0.9500 |
C1—C7 | 1.491 (7) | C7—C8 | 1.499 (8) |
C2—C3 | 1.381 (6) | C8—H8A | 0.9800 |
C2—H2 | 0.9500 | C8—H8B | 0.9800 |
C3—C4 | 1.387 (6) | C8—H8C | 0.9800 |
C3—H3 | 0.9500 | | |
| | | |
C2—C1—C6 | 118.3 (4) | C4—C5—H5 | 120.4 |
C2—C1—C7 | 120.2 (4) | C5—C6—C1 | 120.5 (3) |
C6—C1—C7 | 121.5 (4) | C5—C6—H6 | 119.7 |
C3—C2—C1 | 121.6 (4) | C1—C6—H6 | 119.7 |
C3—C2—H2 | 119.2 | O1—C7—C1 | 119.8 (5) |
C1—C2—H2 | 119.2 | O1—C7—C8 | 121.2 (5) |
C4—C3—C2 | 119.2 (4) | C1—C7—C8 | 118.9 (5) |
C4—C3—H3 | 120.4 | C7—C8—H8A | 109.5 |
C2—C3—H3 | 120.4 | C7—C8—H8B | 109.5 |
C3—C4—C5 | 121.1 (4) | H8A—C8—H8B | 109.5 |
C3—C4—I1 | 120.3 (3) | C7—C8—H8C | 109.5 |
C5—C4—I1 | 118.6 (3) | H8A—C8—H8C | 109.5 |
C6—C5—C4 | 119.3 (3) | H8B—C8—H8C | 109.5 |
C6—C5—H5 | 120.4 | | |
(IM-B)
p-iodoacetophenone polymorph B
top
Crystal data top
C8H7IO | Dx = 2.021 Mg m−3 |
Mr = 246.04 | Melting point: 357-359 K K |
Orthorhombic, Pbca | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2ac 2ab | Cell parameters from 2276 reflections |
a = 9.777 (2) Å | θ = 2.9–27.4° |
b = 8.232 (2) Å | µ = 3.89 mm−1 |
c = 20.089 (5) Å | T = 173 K |
V = 1616.8 (7) Å3 | Plate, colorless |
Z = 8 | 0.25 × 0.20 × 0.01 mm |
F(000) = 928 | |
Data collection top
Siemans SMART area-detector diffractometer | 1855 independent reflections |
Radiation source: fine-focus sealed tube | 1236 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.052 |
ω scans | θmax = 27.5°, θmin = 2.9° |
Absorption correction: multi-scan SADABS; Sheldrick, 1996; Blessing, 1995 | h = −12→12 |
Tmin = 0.41, Tmax = 0.96 | k = −10→10 |
15576 measured reflections | l = −26→26 |
Refinement top
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)] = 0.026 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.070 | H-atom parameters constrained |
S = 1.09 | w = 1/[σ2(Fo2) + (0.019P)2 + 2.68P] where
P = (Fo2 + 2Fc2)/3 |
1855 reflections | (Δ/σ)max = 0.002 |
91 parameters | Δρmax = 0.56 e Å−3 |
0 restraints | Δρmin = −0.45 e Å−3 |
Crystal data top
C8H7IO | V = 1616.8 (7) Å3 |
Mr = 246.04 | Z = 8 |
Orthorhombic, Pbca | Mo Kα radiation |
a = 9.777 (2) Å | µ = 3.89 mm−1 |
b = 8.232 (2) Å | T = 173 K |
c = 20.089 (5) Å | 0.25 × 0.20 × 0.01 mm |
Data collection top
Siemans SMART area-detector diffractometer | 1855 independent reflections |
Absorption correction: multi-scan SADABS; Sheldrick, 1996; Blessing, 1995 | 1236 reflections with I > 2σ(I) |
Tmin = 0.41, Tmax = 0.96 | Rint = 0.052 |
15576 measured reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.026 | 0 restraints |
wR(F2) = 0.070 | H-atom parameters constrained |
S = 1.09 | Δρmax = 0.56 e Å−3 |
1855 reflections | Δρmin = −0.45 e Å−3 |
91 parameters | |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | |
I1 | 0.58879 (2) | 0.25265 (3) | 0.657830 (12) | 0.03254 (10) | |
O1 | 0.5437 (3) | 0.1968 (4) | 1.00741 (14) | 0.0375 (6) | |
C1 | 0.6182 (4) | 0.1533 (4) | 0.89715 (18) | 0.0258 (8) | |
C2 | 0.5141 (4) | 0.2487 (4) | 0.87084 (19) | 0.0299 (7) | |
H2 | 0.4479 | 0.2949 | 0.8998 | 0.036* | |
C3 | 0.5053 (4) | 0.2772 (4) | 0.8031 (2) | 0.0307 (9) | |
H3 | 0.4343 | 0.3436 | 0.7856 | 0.037* | |
C4 | 0.6014 (4) | 0.2080 (4) | 0.76080 (19) | 0.0278 (8) | |
C5 | 0.7058 (4) | 0.1120 (4) | 0.78602 (19) | 0.0294 (8) | |
H5 | 0.7715 | 0.0650 | 0.7570 | 0.035* | |
C6 | 0.7133 (4) | 0.0854 (5) | 0.85411 (19) | 0.0297 (8) | |
H6 | 0.7847 | 0.0196 | 0.8715 | 0.036* | |
C7 | 0.6249 (4) | 0.1289 (4) | 0.97091 (19) | 0.0291 (8) | |
C8 | 0.7347 (4) | 0.0212 (5) | 0.9984 (2) | 0.0427 (10) | |
H8A | 0.7272 | 0.0174 | 1.0470 | 0.064* | |
H8B | 0.8245 | 0.0643 | 0.9859 | 0.064* | |
H8C | 0.7241 | −0.0886 | 0.9803 | 0.064* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
I1 | 0.03458 (15) | 0.03895 (16) | 0.02411 (15) | −0.00124 (12) | 0.00010 (9) | 0.00237 (12) |
O1 | 0.0456 (16) | 0.0407 (14) | 0.0263 (15) | 0.0027 (13) | 0.0019 (13) | −0.0030 (12) |
C1 | 0.0259 (18) | 0.0242 (18) | 0.027 (2) | −0.0038 (14) | 0.0000 (15) | 0.0006 (15) |
C2 | 0.0316 (18) | 0.0314 (18) | 0.0268 (19) | 0.0031 (18) | −0.0001 (15) | −0.0043 (18) |
C3 | 0.0293 (18) | 0.032 (2) | 0.031 (2) | 0.0069 (15) | −0.0040 (15) | 0.0007 (16) |
C4 | 0.0325 (19) | 0.0270 (18) | 0.024 (2) | −0.0057 (15) | −0.0025 (15) | −0.0017 (14) |
C5 | 0.0236 (18) | 0.0341 (19) | 0.030 (2) | 0.0018 (15) | 0.0058 (15) | −0.0007 (17) |
C6 | 0.0282 (19) | 0.032 (2) | 0.029 (2) | 0.0031 (16) | −0.0015 (15) | 0.0040 (16) |
C7 | 0.0344 (19) | 0.0275 (18) | 0.025 (2) | −0.0066 (15) | −0.0029 (17) | 0.0009 (16) |
C8 | 0.046 (3) | 0.048 (3) | 0.034 (2) | 0.007 (2) | −0.002 (2) | 0.0043 (19) |
Geometric parameters (Å, º) top
I1—C4 | 2.105 (4) | C4—C5 | 1.387 (5) |
O1—C7 | 1.217 (5) | C5—C6 | 1.387 (5) |
C1—C6 | 1.387 (5) | C5—H5 | 0.9500 |
C1—C2 | 1.390 (5) | C6—H6 | 0.9500 |
C1—C7 | 1.497 (5) | C7—C8 | 1.497 (5) |
C2—C3 | 1.384 (6) | C8—H8A | 0.9800 |
C2—H2 | 0.9500 | C8—H8B | 0.9800 |
C3—C4 | 1.389 (5) | C8—H8C | 0.9800 |
C3—H3 | 0.9500 | | |
| | | |
C6—C1—C2 | 118.8 (3) | C4—C5—H5 | 120.4 |
C6—C1—C7 | 122.2 (3) | C5—C6—C1 | 121.0 (3) |
C2—C1—C7 | 119.0 (3) | C5—C6—H6 | 119.5 |
C3—C2—C1 | 121.0 (3) | C1—C6—H6 | 119.5 |
C3—C2—H2 | 119.5 | O1—C7—C1 | 120.4 (3) |
C1—C2—H2 | 119.5 | O1—C7—C8 | 121.1 (4) |
C2—C3—C4 | 119.3 (3) | C1—C7—C8 | 118.4 (3) |
C2—C3—H3 | 120.3 | C7—C8—H8A | 109.5 |
C4—C3—H3 | 120.3 | C7—C8—H8B | 109.5 |
C5—C4—C3 | 120.6 (4) | H8A—C8—H8B | 109.5 |
C5—C4—I1 | 120.1 (3) | C7—C8—H8C | 109.5 |
C3—C4—I1 | 119.3 (3) | H8A—C8—H8C | 109.5 |
C6—C5—C4 | 119.3 (3) | H8B—C8—H8C | 109.5 |
C6—C5—H5 | 120.4 | | |
Experimental details
| (ClM) | (BrM) | (IM-A) | (IM-B) |
Crystal data |
Chemical formula | C8H7ClO | C8H7BrO | C8H7IO | C8H7IO |
Mr | 154.59 | 199.05 | 246.04 | 246.04 |
Crystal system, space group | Orthorhombic, P212121 | Monoclinic, Cc | Monoclinic, Cc | Orthorhombic, Pbca |
Temperature (K) | 173 | 173 | 173 | 173 |
a, b, c (Å) | 4.0079 (10), 9.366 (2), 19.787 (5) | 18.635 (5), 6.9554 (17), 5.9035 (15) | 19.425 (5), 7.049 (2), 5.8769 (15) | 9.777 (2), 8.232 (2), 20.089 (5) |
α, β, γ (°) | 90, 90, 90 | 90, 96.36 (1), 90 | 90, 94.41 (1), 90 | 90, 90, 90 |
V (Å3) | 742.8 (3) | 760.5 (3) | 802.3 (4) | 1616.8 (7) |
Z | 4 | 4 | 4 | 8 |
Radiation type | Mo Kα | Mo Kα | Mo Kα | Mo Kα |
µ (mm−1) | 0.44 | 5.33 | 3.92 | 3.89 |
Crystal size (mm) | 0.50 × 0.40 × 0.30 | 0.45 × 0.15 × 0.03 | 0.25 × 0.20 × 0.10 | 0.25 × 0.20 × 0.01 |
|
Data collection |
Diffractometer | Siemens SMART area-detector diffractometer | Siemens SMART area-detector diffractometer | Siemens SMART area-detector diffractometer | Siemans SMART area-detector diffractometer |
Absorption correction | Multi-scan SADABS; Sheldrick, 1996; Blessing, 1995 | Multi-scan (SADABS including thin plate correction; Sheldrick, 1996; Blessing,
1995) | Multi-scan (SADABS; Sheldrick, 1996; Blessing, 1995) | Multi-scan SADABS; Sheldrick, 1996; Blessing, 1995 |
Tmin, Tmax | 0.81, 0.88 | 0.39, 0.85 | 0.38, 0.68 | 0.41, 0.96 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 6382, 1674, 1434 | 3840, 1691, 1569 | 4483, 1821, 1768 | 15576, 1855, 1236 |
Rint | 0.039 | 0.038 | 0.031 | 0.052 |
(sin θ/λ)max (Å−1) | 0.651 | 0.650 | 0.650 | 0.650 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.034, 0.080, 1.03 | 0.032, 0.077, 1.05 | 0.023, 0.060, 1.05 | 0.026, 0.070, 1.09 |
No. of reflections | 1674 | 1691 | 1821 | 1855 |
No. of parameters | 91 | 91 | 91 | 91 |
No. of restraints | 0 | 2 | 2 | 0 |
H-atom treatment | H-atom parameters constrained | H-atom parameters constrained | H-atom parameters constrained | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.17, −0.14 | 0.75, −0.27 | 0.63, −0.31 | 0.56, −0.45 |
Absolute structure | Flack (1983) | Flack(1983),
849 Friedel pairs | Flack (1983) | ? |
Absolute structure parameter | 0.11 (8) | −0.004 (14) | −0.01 (3) | ? |
Table 2. Distances and angles(Å, °) in the C-H···X contacts.a topH | Xb | C-H | C-H···X | H···X | H···X-C | C···X |
Cl-C6H4COCH3 | | | | | | |
*H2 | O1 | 0.95 | 98 | 2.49 | 83 | 2.788 (2) |
*H8A | O1 | 0.98 | 73 | 2.46 | 56 | 2.370 (2) |
H6 | O1i | 0.95 | 167 | 2.57 | 116 | 3.499 (3) |
H8B | O1ii | 0.95 | 166 | 2.46 | 151 | 3.421 (3) |
*H3 | Cl1 | 0.95 | 74 | 2.80 | 46 | 2.697 (2) |
*H5 | Cl1 | 0.95 | 74 | 2.81 | 46 | 2.700 (2) |
H5 | Cl1iii | 0.95 | 163 | 3.02 | 87 | 3.936 (3) |
H8A | Cl1iv | 0.95 | 158 | 3.03 | 121 | 3.951 (3) |
H8A | Cl1v | 0.98 | 121 | 3.13 | 148 | 3.736 (3) |
Br-C6H4COCH3 | | | | | | |
*H2 | O1 | 0.95 | 98 | 2.51 | 82 | 2.799 (6) |
*H8A | O1 | 0.98 | 73 | 2.47 | 56 | 2.377 (6) |
H8B | O1vi | 0.98 | 131 | 2.70 | 106 | 3.430 (6) |
*H3 | Br1 | 0.95 | 76 | 2.94 | 44 | 2.854 (4) |
*H5 | Br1 | 0.95 | 77 | 2.90 | 45 | 2.835 (4) |
H3 | Br1vii | 0.95 | 133 | 3.32 | 66 | 4.024 (4) |
H8A | Br1viii | 0.98 | 148 | 2.96 | 137 | 3.822 (4) |
H8B | Br1ix | 0.98 | 114 | 3.18 | 120 | 3.697 (4) |
H2 | πvii | 0.95 | 125 | 2.81 | 82c | 3.437 (4) |
H5 | πx | 0.95 | 125 | 2.80 | 82c | 3.436 (4) |
I-C6H4COCH3 polymorph A | | | | | | |
*H2 | O1 | 0.95 | 98 | 2.52 | 82 | 2.809 (7) |
*H8A | O1 | 0.98 | 73 | 2.46 | 56 | 2.374 (7) |
H8A | O1vi | 0.98 | 135 | 1.74 | 105 | 3.494 (7) |
*H3 | I1 | 0.95 | 78 | 3.08 | 41 | 3.035 (5) |
*H5 | I1 | 0.95 | 79 | 3.05 | 42 | 3.016 (5) |
H3 | I1vii | 0.95 | 135 | 3.42 | 62 | 4.152 (5) |
H8A | I1viii | 0.98 | 148 | 3.04 | 138 | 3.907 (5) |
H8B | I1ix | 0.98 | 108 | 3.38 | 124 | 3.814 (5) |
H2 | πvii | 0.95 | 121 | 2.92 | 83c | 3.504 (5) |
H5 | πx | 0.95 | 122 | 2.90 | 80c | 3.494 (5) |
I-C6H4COCH3 polymorph B | | | | | | |
*H2 | O1 | 0.95 | 98 | 2.49 | 83 | 2.792 (5) |
*H8A | O1 | 0.98 | 73 | 2.46 | 56 | 2.368 (5) |
H8C | O1xi | 0.98 | 111 | 2.78 | 121 | 3.262 (5) |
*H3 | I1 | 0.95 | 79 | 3.07 | 41 | 3.036 (4) |
*H5 | I1 | 0.95 | 79 | 3.09 | 41 | 3.047 (4) |
H5 | I1xii | 0.95 | 155 | 3.53 | 63 | 4.406 (4) |
H8A | I1xiii | 0.98 | 135 | 3.22 | 139 | 3.969 (4) |
H3 | C5i | 0.95 | 161 | 2.97 | 66c | 3.880 (5) |
H6 | C2xii | 0.95 | 156 | 2.97 | 82c | 3.860 (5) |
a. The entries preceded by * are intramolecular distances for comparison. b. π refers to the center of the C6 ring. c. This angle is the angle between the H···X bond and the plane of the C6 ring. Symmetry codes: (i) 1 − x, 1/2 + y, 3/2 − z; (ii) −x, 1/2 + y, 3/2 − z; (iii) 1/2 + x, 3/2 − y. 1 − z; (iv) 1/2 − x, 1 − y, 1/2 + z; (v) 3/2 − x, 1 − y, 1/2 + z; (vi) x, −y, 1/2 + z; (vii) x, −y, −1/2 + z; (viii) 1/2 + x, 1/2 − y, −1/2 + z; (ix) 1/2 + x, 1/2 − y, 1/2 + z; (x) x, 1 − y, −1/2 + z; (xi) 1 − x, −y, 2 − z; (xii) 3/2 − x, −1/2 + y, z; (xiii) (xiii) x, 1/2 − y, 1/2 + z. |
Table 2. Distances and angles(Å, °) in the C-X···O=C contacts. topcompound | X | O | C-X···O | X···O | X···O=C | ref. |
BrM | Br1 | O1i | 177.4 (4) | 3.320 (4) | 115.2 (3) | a |
IM-A | I1 | O1i | 177.5 (4) | 3.374 (5) | 116.3 (3) | a |
IM-B | I1 | O1ii | 174.7 (4) | 3.082 (4) | 124.0 (3) | a |
IC6H4CHO | I2 | O1 | 174.5 (4) | 3.068 (4) | 119.2 (3) | b |
IC6H4CHO | I2 | O2 | 174.0 (3) | 3.074 (4) | 118.5 (3) | b |
C13H14INO3 | I1 | O4 | 170.9 (4) | 2.987 (4) | 119.5 (3) | c |
C13H14INO3 | I2 | O1 | 166.4 (4) | 3.110 (4) | 120.8 (3) | c |
C13H13I3O4 | I1 | O5 | 159.8 (7) | 3.229 (7) | 143.3 (6) | d |
C13H13I3O4 | I2 | O4 | 176.1 (7) | 3.092 (7) | 113.1 (6) | d |
C13H13I3O4 | I4 | O1 | 158.2 (7) | 3.347 (7) | 143.6 (6) | d |
C13H13I3O4 | I5 | O7 | 146.4 (7) | 3.507 (7) | 106.8 (6) | d |
a. this work. b. Britton & Young, 1997; refcode RIWTOG. c. Horne et al., 1991; refcode KOLWIR. d. Franssen et al., 1996; refcode TATDEX. Symmetry codes: (i) −1/2 + x, 1/2 − y, 1/2 + z; (ii) x, 1/2 − y, −1/2 + z. |
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The structures of p-chloro-, p-bromo (Britton, 1994) and p-iodobenzaldehyde (Britton & Young, 1997) were undertaken in a search for examples of O···X interactions. The iodo compound exhibits such an interaction, with O···I distances of 3.07 Å, but the chloro and bromo compounds have X···X contacts at the halogens and weak C—H···O hydrogen bonds at the aldehyde. We report here the structures of the corresponding acetophenones. This work was undertaken with the expectation that the replacement of the aldehyde H atom with a methyl group would make the O···X interaction more likely in the chloro and bromo compounds. The structure of the bromo compound was reported previously (Lipkowski & Tabaszewska, 1992) but has been repeated here so that all the structure determinations are at the same temperature.
Fig. 1 shows the atom labeling scheme and anisotropic displacement ellipsoids for the chloro, bromo and two polymorphs of the iodo compound (ClM, BrM, IM—A and IM—B, respectively). All of the bond distances and angles are normal, and, with the exception of the C4—X distances, are the same, within experimental error, in all four compounds. The exocyclic C2—C1—C7 angles [mean 119.6 (4)°] are significantly smaller than the C6—C1—C7 angles [mean 121.9 (4)°] The dihedral angles between the rings and the acetyl groups are 4.2 (2) (in ClM), 9.4 (3) (in BrM), 10.6 (4) (in IM—A) and 2.9 (3)° (in IM—B).
ClM forms π stacks parallel to the a axis (see Fig. 2), in which the rings are 3.473 (2) Å apart. The molecules are held together by C—H···O and C—H···Cl interactions. All of the C—H···O interactions shorter than 2.8 Å and all of the C—H···Cl interactions shorter than 3.2 Å are shown as dotted lines in the figure. There are no short O···Cl or Cl···Cl contacts. The Cl atom appears to be a weaker Lewis acid than the CH group in this compound, which is somewhat surprising. The metric data for the interactions are given in Table 1; the intramolecular distances are given for comparision.
The packing in the remaining compounds is significantly different. The CH···Cl interactions in ClM are replaced by CX···OC interactions in BrM, IM—A and IM—B. These interactions are shown in Fig. 3 and the metric data are given in Table 2, along with comparison data from three other compounds with short I···O contacts.
BrM and IM—A are isomorphous, with chains of molecules parallel to the [101] direction held together by X···O interactions. In IM—B there are similar chains parallel to the [001] direction. Successive molecules in the chains are rotated with respect to each other by 44.9 (1)° in BrM, 44.0 (1)° in IM—A and 71.8 (1)° in IM—B. Metric details of intermolecular interactions involving CH groups are included in Table 1. Since the BrM and IM—A structures are isomorphous, further discussion will be confined to the two polymorphs of IM. The description of the packing for BrM is the same as that for IM—A.
In both IM—A and IM—B there are C—H···π interactions. In IM—A, these are from atoms H2 and H5 to the centers of adjoining C6 rings. The two interactions are virtually identical in distance and direction. In IM—A, the molecules pack in such a way as to form layers of molecules, with individual molecules perpendicular to the plane of the layer.
In Fig. 4, the packing in IM—A is shown perpendicular and parallel to one of the layers. As can be seen, the layers are such that one face contains the I atoms, separated by slightly more than the van der Waals distance from the other face, which contains CH3 groups and O atoms. It can also be seen that the C—H···π contacts are almost centric with respect to the benzene rings. In IM—B, there are also C—H···ring contacts, but these are are to individual ring C atoms and at longer distances than those in IM—A. For general discussions of C—H···π contacts see Malone et al. (1997), Nishio et al. (1998) and Desiraju & Steiner (1999).
The most surprising difference between the two polymorphs of IM is the large difference in the two I···O distances in going from IM—A to IM—B (see Table 2). The distance in IM—B is similar to the two independent distances found in p-iodobenzaldehyde (Britton & Young, 1997) and is toward the low end of I···O distances found, although by no means the lowest. A search of the Cambridge Structural Database (Allen, 2002) did not disclose any other examples of two polymorphs with short but differing I···O distances. However, two examples were found where crystallographically independent I···O distances in the same crystal differ by more than 0.1 Å. In ethyl(E)-4[N-(2'-iodophenyl)-N-methylamino]-4-oxabut-2-enoate (Horne et al., 1991), two crystallographically independent molecules form a dimer held together by two I···O interactions; these dimers have approximately twofold symmetry except for the terminal ethyl groups but the two distances are 2.987 (4) and 3.110 (4) Å. In (R,S)-2-methoxytetrahydrofuran-3R-ylmethyl-3,4,5-tri- iodobenzoate (Franssen et al., 1996), two crystallographically independent molecules again form a dimer, with local approximate twofold symmetry. In this case, the two I···O=C contacts in the dimer are similar, 3.229 (7) and 3.347 (7) Å, but two other contacts to O atoms in C/O/C groups are quite different, 3.092 (7) and 3.507 (7) Å. Overall, although the I···O interaction is relatively strong, it is weak enough to be significantly affected by the overall packing.
If the change in the I···C bond lengths were the only difference between the two structures, the volume of IM—B might be expected to be 3.16 (3)% smaller than that in IM—A because of the shortening of the chain length in the I···.·I direction. The experimental difference is that IM—B is larger by 0.76 (6)%; the decrease in the length of the chain is more than offset by increases in the other dimensions. Overall, the packings in the two polymorphs are about equally efficient.
There are no short X···X interactions in either structure. In the BrM and IM—A structures there are planes of Br or I atoms that are separated by slightly more than the usual X···X van der Waals differences. Although these contacts are not unusually short they contribute significantly to the packing energy. On the other hand, in the IM—B structure there are no short I···I distances at all.