Two polymorphic forms of 2,5-bis(4-methoxy­carbonyl­phenyl)-1,3,4-oxa­diazo­le

The title compound [systematic name: di­methyl 4,4'-(1,3,4-oxa­diazole-2,5-diyl)­di­phenyl­enedi­carboxyl­ate], C₁₈H₁₄N₂O₅, crystallizes under similar conditions in two different ortho­rhombic crystalline forms. In both forms, the mol­ecule consists of two equivalent parts. In form 1, these parts are related by a twofold axis of space group Pbcn, and in form 2, by a mirror plane of space group Cmc2₁. The O atom of the oxa­di­azole ring occupies a special position on the twofold axis and on the mirror plane in forms 1 and 2, respectively.

S1. Comment

Compounds containing a 1,3,4-oxadiazole ring as a basic building block are known as scintillator materials or as biologically active agents. Modifications of their chemical structures open up possibilities for new technical applications, for instance, as potential electroluminiscent materials or as active sensor materials. In addition, their optical properties should be taken into account, such as their potential for non-linear processes. In particular, polymers of 1,3,4-oxadiazoles show interesting properties, including high thermal resistivity, good environmental stability, doping possibility or mechanical toughness. The molecule in form 1 of the title compound, (I), is nearly planar. The dihedral angle between the central 1,3,4-oxadiazol ring and the phenyl ring is 4.64 (9)^o. The angle between the phenyl ring and the methoxycarbonyl group is 3.93 (9)°. The corresponding angles in form 2 are 8.86 (9) and 7.58 (8)°, respectively. However, in contrast to the molecule of form 1, the molecule of form 2 adopts a slightly bent shape. As shown in Fig. 2 (top), the molecules in form 1 build up a herring-bone structure, with stacks extended along the x direction. Within the stacks, there are strong π–π interactions between adjacent molecular planes related by a_o translation. The first plane formed by all of the non-H atoms of the molecule is defined by the equation 3.3409x − 0.0y + 18.7644z = 8.0320, with an r.m.s. deviation of 0.0547 Å. The equation of the corresponding translated plane is 3.3409x − 0.0y + 18.7644z = 11.3730. The distance between the two planes is 3.341 (3) Å. The molecular packing of form 2 is shown in Fig. 2 (bottom). The packing is unlike that of form 1 in that no stacking interactions are found in form 2, as there are no molecules arranged parallel to one another. The angle between the planes of two neighbouring molecules related by a c-glide plane is 23.19 (3)°. The equations of the correponding planes are 0.0x + 6.8316y + 1.2121z = 1.604 and 0.0x − 6.8316y + 1.2121z = 2.2101. The r.m.s. deviation above each? plane is 0.1689 Å.

S2. Experimental

A mixture of terephthalic dimethylester (19.5 g) and hydrazine hydrate (5.57 g) was refluxed in methanol (500 ml) for 6 h. The resulting precipitate, viz. therephthalic acid monomethylester monohydrazide, was filtered, dried and refluxed twice in chloroform (100 ml). Therephthalic acid monomethylester monohydrazide (3 g) was stirred in absolute pyridine (50 ml) and therephthalic acid monomethylester chloride (3.07 g) in absolute THF was added dropwise. The reaction mixture was stirred for 6 h at room temperature and then poured in to a solution of water (600 ml) and HCl (50 ml, 37%). The pH value of the solution was corrected to 5, and the precipitated solid product, viz. di-(4-methoxycarbonylbenzol)-hydrazine, was filtered, washed several times with water and dried. Di-(4-methoxycarbonylbenzoyl)-hydrazine (4.8 g) was suspended in phosphoric acid chloride (50 ml) and some drops of DMF were added. The mixture was refluxed for 18 h and preciptated in ice water. The resulting 2,5-di-(4-methoxycarbonyl)-1,3,4-oxadiazole was recrystallized from DMF/ethanol (9:1) giving two different crystalline forms as mentioned above.

S3. Refinement

In the two crystalline forms of (I), the molecules consist of two equivalent parts, which are related by a twofold axis and by a mirror plane in forms 1 and 2, respectively. The O atoms of the oxadiazole rings occupy special positions. H atom positions were calculated geometrically and refined using a riding model.

Computing details

Data collection: CAD-4 Software (Enraf–Nonius, 1977) for (I); CAD-4 (Enraf–Nonius, 1977) for (II). For both compounds, cell refinement: CAD-4; data reduction: MolEN (Fair, 1990); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL-NT (Sheldrick, 1999); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. The molecular structure of (I), showing 50% probability displacement ellipsoids (SHELXTL; Sheldrick, 1999). H-atom labels have been omitted for clarity. [Symmetry codes, for form 1: (i) 2 − x, y, 1/2 − z; for form 2: (i) −x, y, z.]
	Fig. 2. The molecular packing in form 1 (top) and form 2 (bottom).

(I) dimethyl 4,4'-(1,3,4-oxadiazole-2,5-diyl)diphenylenedicarboxylate

Crystal data

C18H14N2O5	Dx = 1.432 Mg m^−3
Mr = 338.31	Mo Kα radiation, λ = 0.71069 Å
Orthorhombic, Pbcn	Cell parameters from 25 reflections
a = 4.735 (1) Å	θ = 12–20°
b = 12.516 (2) Å	µ = 0.11 mm^−1
c = 26.480 (3) Å	T = 293 K
V = 1569.3 (5) Å^3	Needle, colourless
Z = 4	0.42 × 0.13 × 0.11 mm
F(000) = 704

Data collection

Enraf–Nonius CAD-4 diffractometer	Rint = 0.000
Radiation source: fine-focus sealed tube	θmax = 25.0°, θmin = 3.1°
Graphite monochromator	h = 0→5
2θ–ω scans	k = 0→14
1394 measured reflections	l = 0→31
1394 independent reflections	3 standard reflections every 120 min
1052 reflections with I > 2σ(I)	intensity decay: 0.5%

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.050	H-atom parameters constrained
wR(F^2) = 0.164	w = 1/[σ^2(Fo^2) + (0.1156P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.10	(Δ/σ)max = 0.024
1394 reflections	Δρmax = 0.40 e Å^−3
115 parameters	Δρmin = −0.39 e Å^−3
30 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: 0.0065 (6)

Special details

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	1.0000	0.36375 (14)	0.2500	0.0362 (5)
O12	−0.1000 (4)	0.33040 (14)	0.44691 (6)	0.0588 (5)
O13	0.0266 (4)	0.16457 (12)	0.42257 (5)	0.0512 (5)
N3	0.8955 (4)	0.53195 (13)	0.26846 (7)	0.0453 (5)
C2	0.8406 (4)	0.43110 (15)	0.27771 (7)	0.0372 (5)
C6	0.6358 (4)	0.38895 (14)	0.31382 (6)	0.0324 (5)
C7	0.4895 (4)	0.45633 (16)	0.34545 (8)	0.0417 (5)
H1	0.5228	0.5295	0.3439	0.050*
C8	0.2954 (5)	0.41755 (17)	0.37919 (8)	0.0413 (5)
H2	0.1946	0.4646	0.3995	0.050*
C9	0.2484 (4)	0.30767 (14)	0.38315 (7)	0.0381 (5)
C10	0.3999 (5)	0.23987 (13)	0.35125 (7)	0.0391 (5)
H3	0.3702	0.1665	0.3534	0.047*
C11	0.5907 (4)	0.27827 (15)	0.31699 (6)	0.0375 (5)
H4	0.6893	0.2317	0.2961	0.045*
C12	0.0387 (4)	0.27178 (16)	0.42063 (7)	0.0396 (5)
C13	−0.1667 (7)	0.1217 (2)	0.45906 (10)	0.0653 (8)
H5	−0.3006	0.0762	0.4424	0.078*
H6	−0.2647	0.1792	0.4755	0.078*
H7	−0.0640	0.0811	0.4837	0.078*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0496 (12)	0.0218 (9)	0.0371 (10)	0.000	0.0055 (8)	0.000
O12	0.0689 (11)	0.0528 (9)	0.0546 (10)	0.0066 (8)	0.0044 (8)	−0.0098 (8)
O13	0.0694 (11)	0.0398 (9)	0.0443 (9)	−0.0056 (7)	0.0114 (7)	−0.0015 (7)
N3	0.0536 (11)	0.0274 (8)	0.0549 (11)	0.0016 (7)	0.0055 (9)	−0.0005 (7)
C2	0.0451 (9)	0.0306 (9)	0.0358 (9)	0.0019 (7)	−0.0059 (8)	−0.0022 (7)
C6	0.0375 (9)	0.0302 (9)	0.0296 (9)	0.0005 (7)	−0.0013 (7)	−0.0064 (6)
C7	0.0546 (13)	0.0273 (9)	0.0433 (10)	−0.0002 (8)	−0.0022 (8)	−0.0052 (8)
C8	0.0489 (11)	0.0360 (10)	0.0391 (10)	0.0087 (9)	−0.0007 (7)	−0.0100 (8)
C9	0.0487 (11)	0.0214 (9)	0.0444 (11)	−0.0044 (7)	−0.0062 (8)	−0.0027 (7)
C10	0.0551 (13)	0.0207 (8)	0.0415 (10)	−0.0006 (8)	−0.0030 (8)	−0.0067 (7)
C11	0.0498 (12)	0.0280 (9)	0.0347 (10)	−0.0009 (8)	0.0005 (7)	−0.0018 (7)
C12	0.0432 (10)	0.0389 (10)	0.0366 (10)	−0.0057 (8)	−0.0054 (7)	−0.0050 (8)
C13	0.0781 (17)	0.0577 (15)	0.0601 (16)	−0.0132 (13)	0.0098 (14)	0.0054 (12)

Geometric parameters (Å, º)

O1—C2^i	1.349 (2)	C7—H1	0.9300
O1—C2	1.349 (2)	C8—C9	1.397 (3)
O12—C12	1.206 (3)	C8—H2	0.9300
O13—C12	1.344 (2)	C9—C10	1.396 (3)
O13—C13	1.435 (3)	C9—C12	1.474 (3)
N3—C2	1.312 (3)	C10—C11	1.368 (3)
N3—N3^i	1.391 (4)	C10—H3	0.9300
C2—C6	1.460 (3)	C11—H4	0.9300
C6—C7	1.376 (3)	C13—H5	0.9600
C6—C11	1.404 (2)	C13—H6	0.9600
C7—C8	1.370 (3)	C13—H7	0.9600
C2^i—O1—C2	102.6 (2)	C8—C9—C12	117.25 (18)
C12—O13—C13	115.21 (18)	C11—C10—C9	121.82 (17)
C2—N3—N3^i	105.79 (12)	C11—C10—H3	119.1
N3—C2—O1	112.89 (18)	C9—C10—H3	119.1
N3—C2—C6	126.98 (18)	C10—C11—C6	119.13 (18)
O1—C2—C6	120.13 (17)	C10—C11—H4	120.4
C7—C6—C11	119.45 (18)	C6—C11—H4	120.4
C7—C6—C2	120.77 (17)	O12—C12—O13	124.2 (2)
C11—C6—C2	119.78 (17)	O12—C12—C9	124.76 (19)
C8—C7—C6	121.16 (18)	O13—C12—C9	111.01 (17)
C8—C7—H1	119.4	O13—C13—H5	109.5
C6—C7—H1	119.4	O13—C13—H6	109.5
C7—C8—C9	120.30 (19)	H5—C13—H6	109.5
C7—C8—H2	119.8	O13—C13—H7	109.5
C9—C8—H2	119.8	H5—C13—H7	109.5
C10—C9—C8	118.11 (19)	H6—C13—H7	109.5
C10—C9—C12	124.64 (18)

Symmetry code: (i) −x+2, y, −z+1/2.

(II) dimethyl 4,4'-(1,3,4-oxadiazole-2,5-diyl)diphenylenedicarboxylate

Crystal data

C18H14N2O5	Dx = 1.456 Mg m^−3
Mr = 338.31	Mo Kα radiation, λ = 0.71069 Å
Orthorhombic, Cmc21	Cell parameters from 25 reflections
a = 36.708 (4) Å	θ = 12–21°
b = 6.974 (1) Å	µ = 0.11 mm^−1
c = 6.030 (1) Å	T = 293 K
V = 1543.7 (4) Å^3	Needle, colourless
Z = 4	0.39 × 0.11 × 0.10 mm
F(000) = 704

Data collection

Enraf-Nonius CAD-4 diffractometer	Rint = 0.000
Radiation source: fine-focus sealed tube	θmax = 25.0°, θmin = 2.2°
Graphite monochromator	h = 0→43
2θ–ω scans	k = 0→8
1377 measured reflections	l = −7→7
1377 independent reflections	3 standard reflections every 120 min
1058 reflections with I > \2s(I)	intensity decay: 0.3%

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.034	H-atom parameters constrained
wR(F^2) = 0.089	w = 1/[σ^2(Fo^2) + (0.0379P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 0.98	(Δ/σ)max = 0.017
1377 reflections	Δρmax = 0.25 e Å^−3
116 parameters	Δρmin = −0.16 e Å^−3
31 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: 0.0059 (6)

Special details

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	0.0000	0.2528 (4)	0.0020 (4)	0.0350 (7)
O12	0.20010 (6)	0.2069 (4)	−0.0760 (5)	0.0630 (9)
O13	0.17827 (5)	0.3043 (4)	−0.3968 (3)	0.0520 (8)
N3	0.01894 (8)	0.1836 (4)	0.3356 (5)	0.0525 (7)
C2	0.02934 (7)	0.2248 (4)	0.1368 (4)	0.0356 (7)
C6	0.06595 (7)	0.2393 (5)	0.0478 (5)	0.0350 (6)
C7	0.09463 (8)	0.1797 (5)	0.1843 (6)	0.0380 (7)
H7	0.0901	0.1333	0.3263	0.049*
C8	0.12983 (8)	0.1913 (4)	0.1035 (4)	0.0382 (7)
H8	0.1493	0.1535	0.1924	0.050*
C9	0.13627 (7)	0.2584 (5)	−0.1077 (5)	0.0331 (6)
C10	0.10806 (7)	0.3159 (4)	−0.2411 (6)	0.0367 (7)
H10	0.1127	0.3616	−0.3831	0.048*
C11	0.07235 (8)	0.3056 (4)	−0.1635 (5)	0.0347 (7)
H11	0.0531	0.3431	−0.2536	0.045*
C12	0.17562 (7)	0.2568 (5)	−0.1847 (5)	0.0399 (8)
C13	0.21456 (10)	0.2924 (5)	−0.4880 (8)	0.0610 (10)
H131	0.2141	0.3305	−0.6410	0.079*
H132	0.2232	0.1629	−0.4768	0.079*
H133	0.2305	0.3760	−0.4068	0.079*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0364 (15)	0.0407 (14)	0.0280 (16)	0.000	0.000	−0.0014 (14)
O12	0.0435 (15)	0.0786 (19)	0.0670 (18)	0.0056 (14)	−0.0077 (14)	0.0044 (14)
O13	0.0432 (15)	0.0585 (16)	0.0541 (16)	−0.0035 (10)	0.0007 (11)	0.0014 (12)
N3	0.0430 (14)	0.0658 (17)	0.0488 (17)	0.0060 (14)	0.0010 (13)	−0.0017 (15)
C2	0.0267 (15)	0.0444 (16)	0.0357 (17)	0.0008 (13)	−0.0035 (11)	−0.0022 (14)
C6	0.0333 (13)	0.0384 (13)	0.0332 (14)	−0.0022 (10)	−0.0019 (12)	−0.0020 (14)
C7	0.0388 (16)	0.0383 (15)	0.0368 (19)	−0.0014 (12)	−0.0009 (12)	0.0011 (13)
C8	0.0385 (16)	0.0389 (18)	0.0372 (18)	0.0056 (13)	−0.0044 (13)	0.0038 (12)
C9	0.0286 (15)	0.0339 (12)	0.0369 (16)	0.0023 (11)	−0.0019 (12)	−0.0012 (14)
C10	0.0343 (15)	0.0397 (14)	0.0362 (16)	−0.0028 (13)	−0.0017 (13)	0.0068 (14)
C11	0.0339 (16)	0.0371 (14)	0.0332 (17)	0.0002 (13)	−0.0007 (12)	0.0034 (12)
C12	0.0339 (18)	0.0405 (19)	0.0454 (18)	−0.0011 (12)	0.0089 (13)	−0.0014 (17)
C13	0.060 (2)	0.061 (2)	0.062 (3)	0.0019 (14)	0.016 (2)	−0.004 (2)

Geometric parameters (Å, º)

O1—C2	1.363 (3)	C7—H7	0.9300
O1—C2^i	1.363 (3)	C8—C9	1.377 (4)
O12—C12	1.165 (4)	C8—H8	0.9300
O13—C12	1.325 (4)	C9—C10	1.371 (4)
O13—C13	1.444 (4)	C9—C12	1.517 (4)
N3—C2	1.290 (4)	C10—C11	1.394 (4)
N3—N3^i	1.391 (6)	C10—H10	0.9300
C2—C6	1.451 (4)	C11—H11	0.9300
C6—C11	1.375 (4)	C13—H131	0.9600
C6—C7	1.400 (4)	C13—H132	0.9600
C7—C8	1.383 (4)	C13—H133	0.9600
C2—O1—C2^i	104.4 (3)	C8—C9—C12	116.4 (3)
C12—O13—C13	114.9 (3)	C9—C10—C11	119.9 (3)
C2—N3—N3^i	107.19 (19)	C9—C10—H10	120.1
N3—C2—O1	110.6 (3)	C11—C10—H10	120.1
N3—C2—C6	129.3 (3)	C6—C11—C10	119.3 (3)
O1—C2—C6	120.1 (2)	C6—C11—H11	120.4
C11—C6—C7	121.1 (3)	C10—C11—H11	120.4
C11—C6—C2	121.6 (2)	O12—C12—O13	124.1 (3)
C7—C6—C2	117.3 (3)	O12—C12—C9	124.4 (3)
C8—C7—C6	118.6 (3)	O13—C12—C9	111.3 (3)
C8—C7—H7	120.7	O13—C13—H131	109.5
C6—C7—H7	120.7	O13—C13—H132	109.5
C9—C8—C7	120.4 (3)	H131—C13—H132	109.5
C9—C8—H8	119.8	O13—C13—H133	109.5
C7—C8—H8	119.8	H131—C13—H133	109.5
C10—C9—C8	120.8 (3)	H132—C13—H133	109.5
C10—C9—C12	122.8 (3)

Symmetry code: (i) −x, y, z.