Maleic anhydride, redetermination at 130 K

The X-ray crystal structure of the title compound (2,5-furan­dione), C₄H₂O₃, was redetermined at 130 (2) K. The C=C double bond, previously reported to be unusually short, was accurately measured as 1.3322 (9) Å and thus proved to be fairly standard. The relatively high melting point of the compound is attributed to the intermolecular dipole-dipole interactions between carbonyl groups.

Key indicators

• Single-crystal X-ray study
• T = 130 K
• Mean [sigma](C-C) = 0.001 Å
• R factor = 0.027
• wR factor = 0.070
• Data-to-parameter ratio = 21.4

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry

General Notes



REFLT_03
         From the CIF: _diffrn_reflns_theta_max           41.60
         From the CIF: _reflns_number_total               1564
         Count of symmetry unique reflns         1637
         Completeness (_total/calc)             95.54%
         TEST3: Check Friedels for noncentro structure
         Estimate of Friedel pairs measured         0
         Fraction of Friedel pairs measured     0.000
         Are heavy atom types Z>Si present           no
          Please check that the estimate of the number of Friedel pairs is
          correct. If it is not, please give the correct count in the
          _publ_section_exptl_refinement section of the submitted CIF.

---

S1. Comment

The room-temperature structure of maleic anhydride, (I), was first reported by Marsh et al. (1962) with X-ray intensities from Weissenberg photographs. The authors found an unusually short C═C double bond of 1.303 (5) Å. The C—H···O distances were found to be the shortest intermolecular contacts, but these did not fulfill the requirements for hydrogen bonding and were therefore described as normal van der Waals interactions.

The short C═C double bond could not be confirmed by a recent neutron study (Parker et al., 2001), which was also performed at room temperature. With a distance of 1.328 (9) Å, it is in a much more normal range. Based on the very accurate H-atom positions from this study, the absence of C—H···O hydrogen bonds was confirmed. As an explanation for the difference in the melting points of maleic anhydride (M_r 98.06, m.p. 328 K) and heptane (M_r 100.21, m.p. 182 K), the authors suggested dipole–dipole interactions of maleic anhydride molecules in the crystal. The difficulty in this neutron study was the substantial intensity decay in the course of the experiment, probably owing to sublimation of the crystal at room temperature.

In the present X-ray study, a measurement temperature of 130 (2) K was chosen to avoid the sublimation of the crystal and to minimize thermal motion, which could influence the determination of bond geometries. For a more accurate determination of atomic positions, the X-ray intensities were measured up to a resolution of (sinθ/λ)_max = 0.93 Å^-1. This experimental set-up led to a significant decrease in the discrepancy factors, not only for the crystal structure refinement but also for the thermal-motion analysis. The displacement-ellipsoid plot of the molecule is shown in Fig. 1.

The C3═C4 double-bond length, as determined in the present study, is 1.3322 (9) Å. Thermal-motion analysis using the THMA11a program (Schomaker & Trueblood, 1998) results in a weighted R of 0.024 for all U's, indicating that the maleic anhydride molecule behaves as a rigid body. A rigid-body correction of the intramolecular distances is therefore applicable, and leads to a corrected C3═C4 bond length of 1.337 Å. The effect of thermal motion on the bond lengths is much smaller than in the case of the room-temperature neutron study, where the measured value of 1.328 (9) Å for C3═C4 is corrected to 1.344 Å with a rigid-body correction based on non-H atoms. In the latter case, the weighted R for all U's is 0.053.

A closer inspection of the intermolecular interactions in the crystal of the title compound shows that there are short contacts of the negatively charged O6 and O7 atoms with the positively charged C2 and C5 atoms. This type of interaction has been systematically investigated by Allen et al. (1998) for ketones. The stabilizing effect of C═O···C═O interactions is expected to be even higher for anhydrides than for ketones, because of the more positive charge on the anhydride C atoms. The geometrical details of these interactions in maleic anhydride are shown in Fig. 2. According to the nomenclature of Allen et al., the arrangement at O6 (Fig. 2a) is called a perpendicular motif, whereas the arrangement at O7 (Fig. 2 b) exemplifies a sheared parallel motif. In conclusion it can be stated that the crystal structure may be stabilized not only due to the significant dipole moment of the whole molecule, but also due to substantial dipole moments of its functional groups.

The geometry at the positively charged carbonyl-C atoms is not changed by the abovementioned intermolecular approach of negatively charged O atoms. Atoms C2 and C5 have a planar geometry, with the bond-angle sums equal to 360.00°.

S2. Experimental

Crystals were obtained by evaporation of a solution of maleic anhydride in ethyl acetate at room temperature and subsequent cooling to 277 K.

S3. Refinement

The absolute structure could not be determined reliably. Friedel pairs were therefore merged in the refinement.

Computing details

Data collection: COLLECT (Nonius, 1998); cell refinement: HKL-2000 (Otwinowski & Minor, 1997); data reduction: EVALCCD (Duisenberg, 1998) for obtaining the X-ray intensities and SORTAV (Blessing, 1997) for scaling and merging of the X-ray intensities; program(s) used to solve structure: coordinates taken from the literature (Marsh, 1962).; program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 2001); software used to prepare material for publication: manual editing of SHELXL97 output.

Figures

	Fig. 1. Displacement ellipsoid plot of maleic anhydride, drawn at the 50% probability level.
	Fig. 2. Intermolecular carbonyl–carbonyl interactions between the anhydride groups. (a) O6···C5^i 2.9284 (8) Å C2—O6···C5^i 162.50 (5)° and O6···C5^i—O7^i 100.91 (5)° [symmetry code: (i) 0.5 + x, 0.5 - y, 1 - z]; (b) O7···C2^ii 3.0232 (9) Å, C2^ii—O6^ii···C5 54.80 (4)° and C5—O7···C2^ii: 123.13 (5)° [symmetry code: (ii) 0.5 - x, -y, z + 0.5].

2,5-furandione

Crystal data

C4H2O3	Dx = 1.576 Mg m^−3
Mr = 98.06	Melting point: 328 K
Orthorhombic, P212121	Mo Kα radiation, λ = 0.71073 Å
a = 7.0317 (1) Å	Cell parameters from 4665 reflections
b = 11.0201 (2) Å	θ = 1.0–27.5°
c = 5.3323 (1) Å	µ = 0.14 mm^−1
V = 413.20 (1) Å^3	T = 130 K
Z = 4	Needle, colourless
F(000) = 200	0.50 × 0.24 × 0.24 mm

Data collection

Nonius KappaCCD diffractometer	1351 reflections with I > 2σ(I)
Radiation source: rotating anode	Rint = 0.049
Graphite monochromator	θmax = 41.6°, θmin = 3.4°
The intensity data were collected in 4 sets. Set 1 was performed as a combination of 0.5 degrees ϕ– and ω–scans with an exposure time of 3 sec/frame. Sets 2–4 were 1 degree ϕ– and ω–scans with exposure times of 15, 55, and 120 sec/frame, respectively. The detector distances were 35 mm for sets 1 and 2, 45 mm for set 3, and 50 mm for set 4.	h = 0→13
21016 measured reflections	k = 0→20
1564 independent reflections	l = 0→9

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.027	All H-atom parameters refined
wR(F^2) = 0.070	w = 1/σ^2(Fo^2)
S = 0.93	(Δ/σ)max = 0.002
1564 reflections	Δρmax = 0.30 e Å^−3
73 parameters	Δρmin = −0.19 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.050 (13)

Special details

Experimental. The non-reduced setting of the orthorhombic unit cell was chosen to allow a better comparison with the publication of Marsh et al. (1962).

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
O1	0.17378 (7)	0.11746 (5)	0.52620 (9)	0.02156 (9)
C2	0.18203 (9)	0.20519 (5)	0.33955 (11)	0.01989 (10)
C3	0.06114 (10)	0.16553 (6)	0.12852 (12)	0.02140 (10)
C4	−0.01722 (9)	0.05968 (6)	0.19086 (13)	0.02218 (11)
C5	0.05028 (9)	0.02744 (6)	0.44547 (13)	0.02133 (10)
O6	0.27562 (9)	0.29519 (5)	0.36468 (12)	0.03037 (12)
O7	0.01509 (10)	−0.05820 (5)	0.57568 (13)	0.03207 (13)
H8	0.059 (2)	0.2025 (11)	−0.026 (3)	0.041 (4)*
H9	−0.094 (3)	0.0129 (15)	0.096 (4)	0.052 (5)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.02012 (16)	0.02677 (18)	0.01779 (16)	0.00022 (16)	−0.00321 (15)	−0.00087 (15)
C2	0.01909 (19)	0.02145 (19)	0.0191 (2)	−0.00017 (17)	−0.00076 (18)	−0.00337 (18)
C3	0.0238 (2)	0.0229 (2)	0.0175 (2)	0.00111 (19)	−0.0040 (2)	−0.00161 (19)
C4	0.0208 (2)	0.0237 (2)	0.0221 (2)	−0.00069 (19)	−0.00517 (19)	−0.00401 (19)
C5	0.0191 (2)	0.0218 (2)	0.0230 (2)	0.00138 (17)	0.0002 (2)	0.00050 (19)
O6	0.0307 (2)	0.0268 (2)	0.0336 (3)	−0.00836 (19)	−0.0023 (2)	−0.0061 (2)
O7	0.0337 (3)	0.0269 (2)	0.0355 (3)	−0.0002 (2)	0.0019 (2)	0.0093 (2)

Geometric parameters (Å, º)

O1—C5	1.3869 (8)	C4—H9	0.900 (19)
O1—C2	1.3888 (8)	C5—O7	1.1975 (8)
C2—O6	1.1978 (8)	C5—O6^iii	2.9284 (8)
C2—C3	1.4764 (9)	C5—O6^iv	4.3746 (9)
C2—O7^i	3.0232 (9)	O6—C5^ii	2.9284 (8)
C2—O7^ii	4.5632 (8)	O6—C5^i	4.3746 (9)
C3—C4	1.3322 (9)	O7—C2^iv	3.0232 (9)
C3—H8	0.917 (16)	O7—C2^iii	4.5632 (8)
C4—C5	1.4814 (9)
C5—O1—C2	107.56 (5)	O7—C5—O1	120.87 (7)
O6—C2—O1	121.28 (6)	O7—C5—C4	130.85 (7)
O6—C2—C3	130.30 (6)	O1—C5—C4	108.27 (5)
O1—C2—C3	108.42 (5)	O7—C5—O6^iii	100.91 (5)
O6—C2—O7^i	96.24 (5)	O1—C5—O6^iii	80.11 (4)
O1—C2—O7^i	89.42 (4)	C4—C5—O6^iii	86.87 (4)
C3—C2—O7^i	83.82 (4)	O7—C5—O6^iv	28.48 (4)
O6—C2—O7^ii	2.61 (4)	O1—C5—O6^iv	104.33 (4)
O1—C2—O7^ii	122.95 (4)	C4—C5—O6^iv	138.84 (4)
C3—C2—O7^ii	128.56 (4)	O6^iii—C5—O6^iv	123.39 (2)
O7^i—C2—O7^ii	98.125 (17)	C2—O6—C5^ii	162.50 (5)
C4—C3—C2	107.89 (6)	C2—O6—C5^i	54.80 (4)
C4—C3—H8	127.3 (9)	C5^ii—O6—C5^i	122.32 (2)
C2—C3—H8	124.0 (9)	C5—O7—C2^iv	123.13 (5)
C3—C4—C5	107.83 (5)	C5—O7—C2^iii	59.44 (4)
C3—C4—H9	127.4 (12)	C2^iv—O7—C2^iii	140.56 (2)
C5—C4—H9	124.7 (12)
C5—O1—C2—O6	178.07 (6)	O1—C2—O6—C5^ii	12.7 (2)
C5—O1—C2—C3	−1.68 (7)	C3—C2—O6—C5^ii	−167.59 (14)
C5—O1—C2—O7^i	−84.97 (5)	O7^i—C2—O6—C5^ii	−80.42 (18)
C5—O1—C2—O7^ii	175.71 (4)	O7^ii—C2—O6—C5^ii	143.2 (10)
O6—C2—C3—C4	−178.78 (7)	O1—C2—O6—C5^i	99.17 (7)
O1—C2—C3—C4	0.95 (7)	C3—C2—O6—C5^i	−81.13 (7)
O7^i—C2—C3—C4	88.27 (5)	O7^i—C2—O6—C5^i	6.04 (2)
O7^ii—C2—C3—C4	−176.26 (4)	O7^ii—C2—O6—C5^i	−130.3 (8)
C2—C3—C4—C5	0.15 (7)	O1—C5—O7—C2^iv	−47.80 (9)
C2—O1—C5—O7	−178.45 (6)	C4—C5—O7—C2^iv	131.92 (7)
C2—O1—C5—C4	1.77 (7)	O6^iii—C5—O7—C2^iv	−132.73 (4)
C2—O1—C5—O6^iii	−81.58 (4)	O6^iv—C5—O7—C2^iv	12.37 (4)
C2—O1—C5—O6^iv	156.27 (4)	O1—C5—O7—C2^iii	85.48 (6)
C3—C4—C5—O7	179.05 (8)	C4—C5—O7—C2^iii	−94.80 (8)
C3—C4—C5—O1	−1.20 (7)	O6^iii—C5—O7—C2^iii	0.556 (16)
C3—C4—C5—O6^iii	77.32 (5)	O6^iv—C5—O7—C2^iii	145.65 (6)
C3—C4—C5—O6^iv	−141.88 (5)

Symmetry codes: (i) −x+1/2, −y, z−1/2; (ii) x+1/2, −y+1/2, −z+1; (iii) x−1/2, −y+1/2, −z+1; (iv) −x+1/2, −y, z+1/2.