4-Amino derivatives of 7-nitro-2,1,3-benzoxadiazole: the effect of the amino moiety on the structure of fluorophores

The crystal structures of three 4-amino derivatives of 7-nitro-2,1,3-benzoxa­diazole with increasing substituent ring size, viz. 7-nitro-4-(pyrrolidin-1-yl)-2,1,3-benzoxa­diazole, C₁₀H₁₀N₄O₃, 7-nitro-4-(piperidin-1-yl)-2,1,3-benzoxa­diazole, C₁₁H₁₂N₄O₃, and 4-(azepan-1-yl)-7-nitro-2,1,3-benzoxa­diazole, C₁₂H₁₄N₄O₃, have been determined in order to understand their photophysical behaviour. All three were found to crystallize in centrosymmetric space groups. There is considerable electron delocalization compared with the parent compound, although the five-membered oxa­diazole ring apparently does not participate in this. The length of the C-N bond between the amino N atom and the 7-nitro­benzoxa­diazole system is found to be shorter than in similar compounds, as is the C-N_nitro bond. In each structure, the nitro group lies in the plane of the benzoxa­diazole unit.

S1. Comment

Although 4-amino derivatives of 7-nitro-2,1,3-benzoxadiazole (NBD) are considered to be highly efficient fluorophores and have wide applications (Chattopadhyay, 1990), so far only a few crystal structures of these have been reported (Saha & Samanta, 1999a). As benzoxadiazole is considered a complex heterocyclic moiety, the standard input data for initial parameterization for sophisticated theoretical calculations are yet not available. Crystal structure determinations also provide information about whether a crystal exhibits nonlinear optical (NLO) activity: a non-centrosymmetric crystal is a precondition for second-order NLO activity.

It has been shown (Suzuki et al., 1988) that 4-chloro-7-nitrobenzoxadiazole (NBD-chloride) is NLO active. Although the Cl is thought to be part of the π-system and has some electron-donating capacity, the double bonds in the six-membered ring of the benzoxadiazole moiety are localized, i.e. no resonance is detected. It was therefore of interest to determine the structure when this benzoxadiazole unit is attached to a strongly electron-donating group, such as amine, so we report here the crystal structures of three new 4-amino NBD derivatives, 4-nitro-7-(pyrrolidin-1-yl)-2,1,3-benzoxadiazole, (I), 4-nitro-7-(piperidin-1-yl)-2,1,3-benzoxadiazole, (II), and 4-(azepan-1-yl)-7-nitro-2,1,3-benzoxadiazole, (III). \sch

In addition, to follow the details of the structural changes in the intramolecular charge-transfer (ICT) state that accompanies and governs the excited state ICT process, knowledge of ground state crystal structure is important. The present studies were also carried out in order to obtain information on the electron flow and its direction, the change in the order of the C4—N4 bond that connects the amine moiety to the benzoxadiazole subunit in the three derivatives, the pyramidality of the amine N atom, and the change of twist angle with change of substituent amine. It is known that the character of the C4—N4 bond and the configuration of amine N atom determine the photophysical properties of some donor-acceptor (D—A) molecules (Saha & Samanta, 1998). It is also known that the ground state twist angle can be a useful predictor of the excited state conformation (Saha & Samanta, 1999b).

The molecular structures of compounds (I)-(III) are shown in Figs. 1–3, respectively. Unlike the parent compound NBD-chloride, derivatives (I)-(III) are centrosymmetric and show considerable alteration of bond order in the six-membered ring of the benzoxadiazole unit. The C4—C5 bond [1.349 (9) Å] has appreciable double-bond character in NBD-chloride (Suzuki et al., 1988), whereas in the present systems, this bond has considerable single-bond character, with a mean bond length of 1.40 Å. Similarly, the C5—C6 bond in NBD-chloride is 1.435 (9) Å, whereas in (I)-(III) it has an average length of 1.38 Å, indicating that the alteration of bond order of these compounds is due to substitution with a stronger donor.

The C4—N4 bond, which is very important for photophysical behaviour, is found to be considerably shorter in each of (I), (II) and (III). In similar donor-acceptor molecules with ICT states, for example 3,5-dimethyl-4-dimethylaminobenzonitrile, the corresponding C4—N4 bond length is 1.414 (3) Å, and at 173 K it is also twisted by 59.3 (2)° (Heine et al., 1994). However, this is shorter than the corresponding bond in the salt 4-aminobenzonitrile hydrochloride [1.467 (2) Å], which is considered to be a pure single bond (Colapietro et al., 1981). In the case of 4-dimethylaminobenzonitrile (DMABN), the corresponding bond is 1.367 (3) Å, with a twist angle of 10.8 (2)° (Heine et al., 1994), where considerable double-bond character has been predicted on the basis of photophysical properties. For NBD derivatives, the mean C4—N4 length is 1.34 Å. Comparing this with all the data mentioned above, we can conclude that there is a considerable charge flow from donor to acceptor, making the bond appreciably shorter. The double bond character of C4—N4 can also be explained by a formal bond valence approach.

Another noteworthy point is that the C7—N5 bond is considerably shorter in the present NBD derivatives (mean 1.42 Å) compared with NBD-chloride [1.470 (8) Å; Suzuki et al., 1988]. This indicates that the nitro group acts as the acceptor, a conclusion which is supported by the observation that the nitro group is almost coplanar with the benzoxadiazole unit. The adjacent five-membered ring of the benzoxadiazole does not contribute to electron flow, which is evident from the fact that its geometry does not change much on substitution with an amino group. Hence, the dipole moment is directed from the amino to the nitro group, removing the complexity and controversy about the involvement of the benzoxadiazole unit.

Comparing the derivatives studied, it can be seen that (I) has the shortest C4—N4 bond. This is due to the maximum overlap of the amine lone pair with the benzoxadiazole moiety, resulting from the favorable nitrogen conformation retarding rotation around the bond. This observation supports the dynamic NMR data that (I) has a higher barrier to rotation than previously reported compounds (Saha & Samanta, 1998).

The cyclic amino moiety in (II) is found to be in the stable chair conformation. The three angles around the amine N atom indicate the pyramidality at the N atom: in these derivatives, the environment of the amino N atom is almost planar. Furthermore, it can be seen from the data that (III) is more planar than the others. This is due to the lower barrier to inversion for larger rings (Oki, 1985), and also supports the photophysical observations that (III) has the maximum nonradiative rate constant value (Saha & Samanta, 1998).

There is a small increase in the twist angle between the amine and NBD moieties on going from (I) to (III). The maximum twist angle detected for (III) is 10.9 (5)° [τ(C8—N4—C4—C5)], which indicates that the excited state is unlikely to be twisted, contrary to the speculation that a twisted intramolecular charge transfer (TICT) state is involved (Forgues et al., 1993). This supports our earlier findings (Saha & Samanta, 1998).

In summary, from the structure determinations on these three NBD derivatives, we have been able to extract valuable data about the effect of amino substitutions, and some of these data supplement photophysical observations.

S2. Experimental

Compounds (I)-(III) were prepared according to the general procedure of Saha & Samanta (1998). In a typical synthesis, to a solution of NBD-chloride (1 mmol) in ethyl acetate (3 ml) cooled in an icebath was added dropwise a solution of the amine (1.2 mmol) in ethyl acetate (2 ml). After stirring for 30 min in the ice bath, the mixture was stirred for a further 2 h at room temperature. The product, which appeared as a red precipitate in all cases, was filtered off and purified by column chromatography, using a silica gel column and different proportions of hexane and ethyl acetate as eluent. The purified compounds were recrystallized from absolute ethanol by slow evaporation.

S3. Refinement

For all three compounds, H atoms were placed geometrically and refined using a riding model with U_eq(H) = 1.2U_eq(C). C—H distances were fixed at 0.97 Å for methylene H and 0.93 Å for aromatic H.

Computing details

For all compounds, data collection: CAD-4 Software (Enraf-Nonius, 1989); cell refinement: CAD-4 Software; data reduction: Xtal3.5 (Hall et al., 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEX6.0 (McArdle, 1995); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. A view of the molecular structure of (I) showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii. One of the H atoms bound to C9 is wholly obscured by it.
	Fig. 2. A view of the molecular structure of (II) showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii. One H atom on each of C9 and C11 is wholly obscured by the parent atom.
	Fig. 3. A view of the molecular structure of (III) showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.

(I) 4-nitro-7-(pyrrolidin-1-yl)-2,1,3-benzoxadiazole

Crystal data

C10H10N4O3	F(000) = 488
Mr = 234.22	Dx = 1.522 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 7.0305 (12) Å	Cell parameters from 25 reflections
b = 7.686 (2) Å	θ = 11.3–12.6°
c = 18.951 (4) Å	µ = 0.12 mm^−1
β = 93.69 (2)°	T = 293 K
V = 1022.0 (4) Å^3	Plate, red
Z = 4	0.70 × 0.40 × 0.20 mm

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→8
ω scans	k = 0→9
1792 measured reflections	l = −22→22
1792 independent reflections	3 standard reflections every 90 min
973 reflections with I > 2σ(I)	intensity decay: none

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.040	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.130	H-atom parameters constrained
S = 1.11	w = 1/[σ^2(Fo^2) + (0.0537P)^2 + 0.1481P] where P = (Fo^2 + 2Fc^2)/3
1792 reflections	(Δ/σ)max = 0.012
154 parameters	Δρmax = 0.17 e Å^−3
0 restraints	Δρmin = −0.17 e Å^−3

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
O2	0.2690 (3)	0.8573 (3)	−0.09335 (10)	0.0741 (6)
O3	−0.4294 (3)	0.5178 (3)	−0.09702 (11)	0.0857 (7)
O4	−0.2182 (3)	0.6025 (3)	−0.16753 (11)	0.0862 (7)
N1	0.1009 (4)	0.7768 (3)	−0.11805 (12)	0.0653 (7)
N3	0.2838 (3)	0.8727 (3)	−0.02154 (11)	0.0606 (6)
N4	0.1732 (3)	0.8478 (3)	0.12620 (10)	0.0490 (6)
N5	−0.2778 (4)	0.5912 (3)	−0.10808 (13)	0.0635 (6)
C1	0.0126 (4)	0.7436 (3)	−0.06054 (12)	0.0477 (6)
C3	0.1267 (3)	0.8039 (3)	−0.00047 (12)	0.0450 (6)
C4	0.0666 (3)	0.7902 (3)	0.07072 (12)	0.0438 (6)
C5	−0.1128 (4)	0.7131 (4)	0.07570 (13)	0.0523 (7)
H5	−0.1612	0.7024	0.1200	0.063*
C6	−0.2204 (4)	0.6522 (3)	0.01718 (14)	0.0541 (7)
H6	−0.3375	0.6010	0.0243	0.065*
C7	−0.1646 (4)	0.6630 (3)	−0.05071 (13)	0.0506 (7)
C8	0.1109 (4)	0.8452 (4)	0.19888 (13)	0.0644 (8)
H8A	0.1066	0.7273	0.2169	0.077*
H8B	−0.0139	0.8980	0.2011	0.077*
C9	0.2615 (5)	0.9508 (5)	0.23955 (15)	0.0859 (11)
H9A	0.2267	1.0729	0.2399	0.103*
H9B	0.2798	0.9100	0.2879	0.103*
C10	0.4362 (5)	0.9238 (5)	0.20103 (15)	0.0814 (10)
H10A	0.4990	0.8162	0.2158	0.098*
H10B	0.5247	1.0194	0.2097	0.098*
C11	0.3690 (4)	0.9159 (4)	0.12478 (13)	0.0541 (7)
H11A	0.3695	1.0305	0.1033	0.065*
H11B	0.4483	0.8386	0.0988	0.065*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O2	0.0781 (14)	0.0960 (16)	0.0503 (11)	−0.0215 (12)	0.0204 (10)	−0.0017 (11)
O3	0.0661 (14)	0.0942 (18)	0.0944 (17)	−0.0215 (13)	−0.0123 (12)	−0.0102 (13)
O4	0.1051 (18)	0.0964 (18)	0.0551 (13)	−0.0156 (14)	−0.0114 (12)	−0.0004 (12)
N1	0.0751 (16)	0.0708 (17)	0.0505 (13)	−0.0076 (13)	0.0079 (12)	−0.0022 (12)
N3	0.0655 (15)	0.0697 (16)	0.0481 (13)	−0.0102 (12)	0.0150 (10)	−0.0024 (11)
N4	0.0518 (13)	0.0536 (13)	0.0421 (11)	−0.0012 (10)	0.0062 (9)	0.0009 (10)
N5	0.0699 (17)	0.0553 (15)	0.0630 (16)	0.0027 (13)	−0.0123 (13)	−0.0009 (12)
C1	0.0585 (16)	0.0430 (15)	0.0422 (13)	0.0086 (12)	0.0081 (12)	0.0051 (11)
C3	0.0475 (14)	0.0433 (15)	0.0446 (13)	0.0006 (12)	0.0068 (11)	0.0017 (11)
C4	0.0472 (14)	0.0406 (14)	0.0442 (14)	0.0045 (11)	0.0065 (11)	0.0035 (11)
C5	0.0517 (15)	0.0585 (17)	0.0476 (14)	0.0004 (13)	0.0096 (11)	0.0014 (12)
C6	0.0449 (15)	0.0533 (17)	0.0646 (17)	0.0004 (12)	0.0067 (13)	0.0018 (13)
C7	0.0505 (15)	0.0456 (15)	0.0549 (16)	0.0046 (12)	−0.0042 (12)	0.0002 (12)
C8	0.078 (2)	0.072 (2)	0.0436 (15)	−0.0106 (16)	0.0129 (14)	0.0018 (14)
C9	0.101 (3)	0.107 (3)	0.0489 (17)	−0.027 (2)	0.0033 (17)	−0.0054 (18)
C10	0.080 (2)	0.101 (3)	0.0614 (19)	−0.017 (2)	−0.0090 (16)	0.0035 (18)
C11	0.0514 (15)	0.0572 (17)	0.0534 (15)	−0.0040 (13)	0.0003 (12)	0.0000 (13)

Geometric parameters (Å, º)

O2—N3	1.363 (3)	C5—H5	0.9300
O2—N1	1.388 (3)	C6—C7	1.371 (4)
O3—N5	1.236 (3)	C6—H6	0.9300
O4—N5	1.230 (3)	C8—C9	1.506 (4)
N1—C1	1.314 (4)	C8—H8A	0.9700
N3—C3	1.310 (3)	C8—H8B	0.9700
N4—C4	1.328 (4)	C9—C10	1.484 (5)
N4—C8	1.472 (3)	C9—H9A	0.9700
N4—C11	1.474 (3)	C9—H9B	0.9700
N5—C7	1.417 (4)	C10—C11	1.492 (4)
C1—C7	1.414 (4)	C10—H10A	0.9700
C1—C3	1.427 (4)	C10—H10B	0.9700
C3—C4	1.443 (3)	C11—H11A	0.9700
C4—C5	1.402 (3)	C11—H11B	0.9700
C5—C6	1.383 (4)
N3—O2—N1	112.6 (2)	C1—C7—N5	121.7 (3)
C1—N1—O2	104.1 (2)	N4—C8—C9	103.3 (2)
C3—N3—O2	104.9 (3)	N4—C8—H8A	111.1
C4—N4—C8	123.3 (2)	C9—C8—H8A	111.1
C4—N4—C11	125.8 (2)	N4—C8—H8B	111.1
C8—N4—C11	110.9 (3)	C9—C8—H8B	111.1
O4—N5—O3	122.4 (3)	H8A—C8—H8B	109.1
O4—N5—C7	117.9 (3)	C10—C9—C8	104.5 (3)
O3—N5—C7	119.7 (3)	C10—C9—H9A	110.9
N1—C1—C7	131.4 (3)	C8—C9—H9A	110.9
N1—C1—C3	109.1 (2)	C10—C9—H9B	110.9
C7—C1—C3	119.5 (2)	C8—C9—H9B	110.9
N3—C3—C1	109.2 (2)	H9A—C9—H9B	108.9
N3—C3—C4	128.1 (3)	C9—C10—C11	105.1 (3)
C1—C3—C4	122.6 (2)	C9—C10—H10A	110.7
N4—C4—C5	123.5 (2)	C11—C10—H10A	110.7
N4—C4—C3	122.1 (2)	C9—C10—H10B	110.7
C5—C4—C3	114.4 (3)	C11—C10—H10B	110.7
C6—C5—C4	122.5 (3)	H10A—C10—H10B	108.8
C6—C5—H5	118.8	N4—C11—C10	103.6 (3)
C4—C5—H5	118.8	N4—C11—H11A	111.0
C7—C6—C5	123.9 (3)	C10—C11—H11A	111.0
C7—C6—H6	118.1	N4—C11—H11B	111.0
C5—C6—H6	118.1	C10—C11—H11B	111.0
C6—C7—C1	117.2 (3)	H11A—C11—H11B	109.0
C6—C7—N5	121.1 (3)
N3—O2—N1—C1	0.2 (3)	C3—C4—C5—C6	1.3 (4)
N1—O2—N3—C3	−0.3 (3)	C4—C5—C6—C7	−0.9 (4)
O2—N1—C1—C7	−179.8 (3)	C5—C6—C7—C1	−0.9 (4)
O2—N1—C1—C3	0.0 (3)	C5—C6—C7—N5	177.2 (2)
O2—N3—C3—C1	0.3 (3)	N1—C1—C7—C6	−178.1 (3)
O2—N3—C3—C4	−178.3 (2)	C3—C1—C7—C6	2.1 (3)
N1—C1—C3—N3	−0.2 (3)	N1—C1—C7—N5	3.9 (4)
C7—C1—C3—N3	179.7 (2)	C3—C1—C7—N5	−176.0 (2)
N1—C1—C3—C4	178.5 (2)	O4—N5—C7—C6	−178.7 (2)
C7—C1—C3—C4	−1.7 (4)	O3—N5—C7—C6	0.1 (4)
C8—N4—C4—C5	−3.2 (4)	O4—N5—C7—C1	−0.7 (4)
C11—N4—C4—C5	174.4 (2)	O3—N5—C7—C1	178.1 (2)
C8—N4—C4—C3	176.2 (2)	C4—N4—C8—C9	−170.2 (3)
C11—N4—C4—C3	−6.2 (4)	C11—N4—C8—C9	11.8 (3)
N3—C3—C4—N4	−1.1 (4)	N4—C8—C9—C10	−29.3 (3)
C1—C3—C4—N4	−179.5 (2)	C8—C9—C10—C11	36.5 (4)
N3—C3—C4—C5	178.4 (3)	C4—N4—C11—C10	−167.7 (3)
C1—C3—C4—C5	0.0 (3)	C8—N4—C11—C10	10.1 (3)
N4—C4—C5—C6	−179.3 (2)	C9—C10—C11—N4	−28.6 (3)

(II) 4-nitro-7-(piperidin-1-yl)-2,1,3-benzoxadiazole

Crystal data

C11H12N4O3	F(000) = 520
Mr = 248.25	Dx = 1.475 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 6.7644 (19) Å	Cell parameters from 25 reflections
b = 21.277 (6) Å	θ = 7.8–10.4°
c = 7.788 (6) Å	µ = 0.11 mm^−1
β = 94.22 (5)°	T = 293 K
V = 1117.8 (10) Å^3	Plate, red
Z = 4	0.40 × 0.29 × 0.16 mm

Data collection

Enraf-Nonius CAD-4 diffractometer	Rint = 0.137
Radiation source: fine-focus sealed tube	θmax = 25.0°, θmin = 1.9°
Graphite monochromator	h = 0→8
ω scans	k = 0→25
2122 measured reflections	l = −9→9
1955 independent reflections	3 standard reflections every 90 min
732 reflections with I > 2σ(I)	intensity decay: none

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.069	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.224	H-atom parameters constrained
S = 1.05	w = 1/[σ^2(Fo^2) + (0.0751P)^2] where P = (Fo^2 + 2Fc^2)/3
1955 reflections	(Δ/σ)max = 0.005
163 parameters	Δρmax = 0.25 e Å^−3
0 restraints	Δρmin = −0.28 e Å^−3

Special details

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
O2	1.2708 (6)	0.1956 (2)	0.5115 (5)	0.0705 (13)
O3	0.8613 (7)	0.41196 (19)	0.2956 (6)	0.0708 (13)
O4	1.1369 (7)	0.3836 (2)	0.4337 (6)	0.0762 (14)
N1	1.2214 (7)	0.2591 (2)	0.4846 (7)	0.0627 (15)
N3	1.1279 (7)	0.1568 (2)	0.4370 (6)	0.0597 (14)
N4	0.7555 (7)	0.1166 (2)	0.2282 (6)	0.0520 (13)
N5	0.9771 (8)	0.3714 (2)	0.3535 (6)	0.0555 (13)
C1	1.0516 (8)	0.2576 (3)	0.3919 (7)	0.0464 (14)
C3	0.9927 (7)	0.1935 (3)	0.3611 (6)	0.0396 (13)
C4	0.8069 (8)	0.1761 (3)	0.2639 (7)	0.0427 (13)
C5	0.6909 (8)	0.2287 (3)	0.2131 (7)	0.0500 (15)
H5	0.5673	0.2218	0.1557	0.060*
C6	0.7508 (8)	0.2900 (3)	0.2441 (7)	0.0512 (16)
H6	0.6664	0.3221	0.2035	0.061*
C7	0.9263 (8)	0.3065 (3)	0.3306 (6)	0.0433 (13)
C8	0.5635 (8)	0.1013 (3)	0.1391 (8)	0.0626 (18)
H8A	0.5831	0.0865	0.0239	0.075*
H8B	0.4820	0.1389	0.1292	0.075*
C9	0.4588 (8)	0.0514 (3)	0.2361 (8)	0.0561 (16)
H9A	0.4207	0.0688	0.3440	0.067*
H9B	0.3389	0.0388	0.1689	0.067*
C10	0.5864 (8)	−0.0050 (3)	0.2723 (7)	0.0534 (15)
H10A	0.6073	−0.0263	0.1650	0.064*
H10B	0.5193	−0.0339	0.3447	0.064*
C11	0.7837 (8)	0.0128 (3)	0.3607 (7)	0.0536 (15)
H11A	0.8671	−0.0242	0.3739	0.064*
H11B	0.7645	0.0292	0.4745	0.064*
C12	0.8844 (7)	0.0617 (3)	0.2572 (7)	0.0496 (15)
H12A	1.0080	0.0744	0.3185	0.060*
H12B	0.9147	0.0441	0.1474	0.060*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O2	0.053 (3)	0.079 (3)	0.075 (3)	0.004 (2)	−0.022 (2)	−0.008 (3)
O3	0.082 (3)	0.056 (3)	0.075 (3)	0.008 (2)	0.006 (3)	0.002 (2)
O4	0.071 (3)	0.072 (3)	0.084 (3)	−0.022 (2)	−0.010 (3)	−0.010 (3)
N1	0.053 (3)	0.072 (4)	0.061 (3)	0.006 (3)	−0.004 (3)	−0.007 (3)
N3	0.043 (3)	0.070 (3)	0.064 (3)	−0.001 (3)	−0.015 (2)	−0.014 (3)
N4	0.042 (3)	0.056 (3)	0.056 (3)	−0.002 (2)	−0.007 (2)	0.000 (3)
N5	0.064 (4)	0.055 (3)	0.048 (3)	−0.002 (3)	0.008 (3)	−0.001 (3)
C1	0.038 (3)	0.062 (4)	0.039 (3)	−0.005 (3)	0.000 (3)	−0.005 (3)
C3	0.030 (3)	0.053 (3)	0.035 (3)	0.006 (3)	0.002 (2)	−0.004 (3)
C4	0.037 (3)	0.056 (4)	0.035 (3)	0.003 (3)	0.003 (2)	−0.004 (3)
C5	0.045 (3)	0.059 (4)	0.045 (3)	0.001 (3)	−0.006 (3)	−0.004 (3)
C6	0.053 (4)	0.061 (4)	0.039 (3)	0.003 (3)	−0.002 (3)	0.008 (3)
C7	0.042 (3)	0.051 (3)	0.037 (3)	−0.007 (3)	0.004 (3)	−0.004 (3)
C8	0.043 (3)	0.063 (4)	0.079 (5)	−0.002 (3)	−0.014 (3)	−0.003 (4)
C9	0.041 (3)	0.069 (4)	0.058 (4)	−0.005 (3)	−0.001 (3)	−0.012 (3)
C10	0.049 (3)	0.065 (4)	0.047 (4)	−0.001 (3)	0.005 (3)	−0.005 (3)
C11	0.054 (4)	0.058 (4)	0.048 (3)	0.004 (3)	−0.002 (3)	−0.002 (3)
C12	0.039 (3)	0.054 (4)	0.056 (4)	0.000 (3)	−0.001 (3)	−0.007 (3)

Geometric parameters (Å, º)

O2—N3	1.368 (6)	C6—C7	1.367 (7)
O2—N1	1.402 (6)	C6—H6	0.9300
O3—N5	1.229 (6)	C8—C9	1.510 (8)
O4—N5	1.235 (6)	C8—H8A	0.9700
N1—C1	1.311 (6)	C8—H8B	0.9700
N3—C3	1.310 (6)	C9—C10	1.493 (7)
N4—C4	1.337 (6)	C9—H9A	0.9700
N4—C8	1.463 (6)	C9—H9B	0.9700
N4—C12	1.465 (6)	C10—C11	1.503 (7)
N5—C7	1.431 (7)	C10—H10A	0.9700
C1—C7	1.402 (7)	C10—H10B	0.9700
C1—C3	1.437 (7)	C11—C12	1.510 (7)
C3—C4	1.466 (7)	C11—H11A	0.9700
C4—C5	1.406 (7)	C11—H11B	0.9700
C5—C6	1.382 (7)	C12—H12A	0.9700
C5—H5	0.9300	C12—H12B	0.9700
N3—O2—N1	111.4 (4)	C9—C8—H8A	109.5
C1—N1—O2	104.4 (5)	N4—C8—H8B	109.5
C3—N3—O2	106.2 (5)	C9—C8—H8B	109.5
C4—N4—C8	121.2 (5)	H8A—C8—H8B	108.1
C4—N4—C12	125.5 (4)	C10—C9—C8	112.0 (5)
C8—N4—C12	113.2 (4)	C10—C9—H9A	109.2
O3—N5—O4	123.3 (5)	C8—C9—H9A	109.2
O3—N5—C7	119.4 (5)	C10—C9—H9B	109.2
O4—N5—C7	117.3 (5)	C8—C9—H9B	109.2
N1—C1—C7	130.8 (5)	H9A—C9—H9B	107.9
N1—C1—C3	109.6 (5)	C9—C10—C11	111.5 (5)
C7—C1—C3	119.6 (5)	C9—C10—H10A	109.3
N3—C3—C1	108.3 (5)	C11—C10—H10A	109.3
N3—C3—C4	128.8 (5)	C9—C10—H10B	109.3
C1—C3—C4	122.8 (5)	C11—C10—H10B	109.3
N4—C4—C5	124.3 (5)	H10A—C10—H10B	108.0
N4—C4—C3	123.1 (5)	C10—C11—C12	110.4 (5)
C5—C4—C3	112.6 (5)	C10—C11—H11A	109.6
C6—C5—C4	123.5 (5)	C12—C11—H11A	109.6
C6—C5—H5	118.3	C10—C11—H11B	109.6
C4—C5—H5	118.3	C12—C11—H11B	109.6
C7—C6—C5	124.1 (5)	H11A—C11—H11B	108.1
C7—C6—H6	118.0	N4—C12—C11	110.2 (4)
C5—C6—H6	118.0	N4—C12—H12A	109.6
C6—C7—C1	117.3 (5)	C11—C12—H12A	109.6
C6—C7—N5	120.0 (5)	N4—C12—H12B	109.6
C1—C7—N5	122.6 (5)	C11—C12—H12B	109.6
N4—C8—C9	110.6 (5)	H12A—C12—H12B	108.1
N4—C8—H8A	109.5
N3—O2—N1—C1	−1.1 (6)	C4—C5—C6—C7	−1.7 (9)
N1—O2—N3—C3	1.3 (6)	C5—C6—C7—C1	−0.3 (8)
O2—N1—C1—C7	177.4 (5)	C5—C6—C7—N5	178.8 (5)
O2—N1—C1—C3	0.4 (6)	N1—C1—C7—C6	−176.4 (6)
O2—N3—C3—C1	−1.0 (6)	C3—C1—C7—C6	0.4 (7)
O2—N3—C3—C4	−179.3 (5)	N1—C1—C7—N5	4.5 (9)
N1—C1—C3—N3	0.4 (6)	C3—C1—C7—N5	−178.7 (5)
C7—C1—C3—N3	−177.0 (5)	O3—N5—C7—C6	0.4 (8)
N1—C1—C3—C4	178.8 (5)	O4—N5—C7—C6	179.5 (5)
C7—C1—C3—C4	1.4 (8)	O3—N5—C7—C1	179.5 (5)
C8—N4—C4—C5	−3.5 (9)	O4—N5—C7—C1	−1.4 (8)
C12—N4—C4—C5	170.6 (5)	C4—N4—C8—C9	−129.1 (5)
C8—N4—C4—C3	176.5 (5)	C12—N4—C8—C9	56.1 (6)
C12—N4—C4—C3	−9.3 (9)	N4—C8—C9—C10	−52.9 (6)
N3—C3—C4—N4	−5.1 (9)	C8—C9—C10—C11	53.1 (6)
C1—C3—C4—N4	176.9 (5)	C9—C10—C11—C12	−54.5 (6)
N3—C3—C4—C5	175.0 (5)	C4—N4—C12—C11	127.3 (6)
C1—C3—C4—C5	−3.0 (8)	C8—N4—C12—C11	−58.1 (6)
N4—C4—C5—C6	−176.8 (5)	C10—C11—C12—N4	56.2 (6)
C3—C4—C5—C6	3.1 (8)

(III) 4-(azepan-1-yl)-7-nitro-2,1,3-benzoxadiazole

Crystal data

C12H14N4O3	F(000) = 552
Mr = 262.27	Dx = 1.444 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 7.4909 (16) Å	Cell parameters from 25 reflections
b = 10.8002 (14) Å	θ = 9.3–10.6°
c = 15.1001 (19) Å	µ = 0.11 mm^−1
β = 98.958 (14)°	T = 293 K
V = 1206.7 (3) Å^3	Plate, red
Z = 4	0.32 × 0.21 × 0.10 mm

Data collection

Enraf-Nonius CAD-4 diffractometer	Rint = 0.000
Radiation source: fine-focus sealed tube	θmax = 25.0°, θmin = 2.3°
Graphite monochromator	h = 0→8
ω scans	k = 0→12
2115 measured reflections	l = −17→17
2115 independent reflections	3 standard reflections every 90 min
1043 reflections with I > 2σ(I)	intensity decay: none

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)] = 0.051	H-atom parameters constrained
wR(F^2) = 0.174	w = 1/[σ^2(Fo^2) + (0.0918P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.03	(Δ/σ)max = 0.001
2115 reflections	Δρmax = 0.22 e Å^−3
173 parameters	Δρmin = −0.20 e Å^−3
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.010 (3)

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
O2	0.8728 (4)	−0.1494 (2)	0.06047 (15)	0.0596 (7)
O3	0.4812 (4)	−0.0492 (2)	−0.27555 (16)	0.0706 (8)
O4	0.6308 (4)	−0.1977 (2)	−0.20052 (18)	0.0749 (9)
N1	0.7892 (4)	−0.1647 (2)	−0.02781 (18)	0.0523 (8)
N3	0.8594 (4)	−0.0311 (2)	0.09053 (17)	0.0503 (8)
N4	0.7419 (4)	0.2345 (2)	0.08964 (17)	0.0465 (7)
N5	0.5748 (4)	−0.0910 (3)	−0.20698 (18)	0.0533 (8)
C1	0.7237 (4)	−0.0540 (3)	−0.0513 (2)	0.0398 (7)
C3	0.7682 (4)	0.0303 (3)	0.02302 (19)	0.0382 (7)
C4	0.7099 (4)	0.1577 (3)	0.0190 (2)	0.0426 (8)
C5	0.6087 (5)	0.1927 (3)	−0.0638 (2)	0.0493 (9)
H5	0.5680	0.2739	−0.0710	0.059*
C6	0.5672 (4)	0.1114 (3)	−0.1349 (2)	0.0483 (8)
H6	0.4989	0.1408	−0.1875	0.058*
C7	0.6217 (4)	−0.0107 (3)	−0.13214 (19)	0.0446 (8)
C8	0.6450 (5)	0.3529 (3)	0.0889 (3)	0.0588 (10)
H8A	0.6238	0.3713	0.1493	0.071*
H8B	0.5283	0.3447	0.0513	0.071*
C9	0.7461 (6)	0.4605 (3)	0.0551 (3)	0.0702 (12)
H9A	0.7917	0.4345	0.0013	0.084*
H9B	0.6616	0.5277	0.0385	0.084*
C10	0.9029 (6)	0.5090 (3)	0.1219 (3)	0.0740 (12)
H10A	0.9660	0.5715	0.0926	0.089*
H10B	0.8548	0.5490	0.1706	0.089*
C11	1.0379 (5)	0.4115 (3)	0.1611 (3)	0.0688 (11)
H11A	1.1400	0.4523	0.1968	0.083*
H11B	1.0825	0.3688	0.1124	0.083*
C12	0.9609 (5)	0.3161 (3)	0.2194 (3)	0.0620 (10)
H12A	1.0582	0.2871	0.2646	0.074*
H12B	0.8734	0.3572	0.2503	0.074*
C13	0.8711 (5)	0.2050 (3)	0.1709 (2)	0.0560 (9)
H13A	0.9640	0.1511	0.1543	0.067*
H13B	0.8079	0.1594	0.2120	0.067*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O2	0.0781 (17)	0.0429 (13)	0.0536 (14)	0.0124 (12)	−0.0033 (13)	0.0003 (11)
O3	0.0793 (19)	0.0814 (19)	0.0446 (14)	−0.0087 (15)	−0.0110 (14)	0.0003 (13)
O4	0.096 (2)	0.0536 (16)	0.0683 (18)	0.0026 (15)	−0.0074 (15)	−0.0182 (13)
N1	0.0625 (19)	0.0471 (17)	0.0459 (16)	0.0037 (14)	0.0039 (14)	−0.0012 (13)
N3	0.0648 (19)	0.0384 (15)	0.0454 (15)	0.0111 (14)	0.0014 (14)	0.0014 (12)
N4	0.0513 (16)	0.0389 (15)	0.0475 (15)	0.0031 (12)	0.0022 (13)	−0.0007 (12)
N5	0.0519 (18)	0.062 (2)	0.0448 (17)	−0.0109 (15)	0.0033 (14)	−0.0028 (14)
C1	0.0383 (17)	0.0390 (17)	0.0432 (17)	0.0035 (14)	0.0101 (14)	0.0004 (14)
C3	0.0399 (17)	0.0365 (16)	0.0383 (16)	0.0024 (14)	0.0062 (14)	0.0044 (13)
C4	0.0427 (18)	0.0406 (17)	0.0449 (17)	0.0007 (14)	0.0085 (14)	0.0017 (15)
C5	0.054 (2)	0.0419 (18)	0.049 (2)	0.0092 (16)	−0.0005 (16)	0.0076 (15)
C6	0.048 (2)	0.0496 (19)	0.0441 (18)	−0.0006 (16)	−0.0020 (15)	0.0089 (15)
C7	0.0399 (18)	0.0536 (19)	0.0390 (17)	−0.0024 (15)	0.0025 (14)	0.0027 (15)
C8	0.052 (2)	0.0454 (19)	0.076 (2)	0.0111 (17)	0.0037 (19)	−0.0055 (18)
C9	0.078 (3)	0.044 (2)	0.085 (3)	0.011 (2)	0.004 (2)	0.0040 (19)
C10	0.073 (3)	0.047 (2)	0.106 (3)	−0.006 (2)	0.024 (2)	−0.014 (2)
C11	0.058 (2)	0.058 (2)	0.090 (3)	−0.007 (2)	0.008 (2)	−0.018 (2)
C12	0.067 (2)	0.058 (2)	0.060 (2)	0.0007 (19)	0.0033 (19)	−0.0159 (18)
C13	0.067 (2)	0.053 (2)	0.0459 (19)	0.0031 (18)	0.0000 (18)	0.0011 (16)

Geometric parameters (Å, º)

O2—N3	1.365 (3)	C8—C9	1.518 (5)
O2—N1	1.392 (4)	C8—H8A	0.9700
O3—N5	1.242 (3)	C8—H8B	0.9700
O4—N5	1.226 (4)	C9—C10	1.518 (6)
N1—C1	1.320 (4)	C9—H9A	0.9700
N3—C3	1.314 (4)	C9—H9B	0.9700
N4—C4	1.344 (4)	C10—C11	1.515 (5)
N4—C8	1.469 (4)	C10—H10A	0.9700
N4—C13	1.475 (4)	C10—H10B	0.9700
N5—C7	1.424 (4)	C11—C12	1.526 (5)
C1—C7	1.415 (4)	C11—H11A	0.9700
C1—C3	1.443 (4)	C11—H11B	0.9700
C3—C4	1.442 (4)	C12—C13	1.508 (5)
C4—C5	1.409 (4)	C12—H12A	0.9700
C5—C6	1.384 (4)	C12—H12B	0.9700
C5—H5	0.9300	C13—H13A	0.9700
C6—C7	1.379 (4)	C13—H13B	0.9700
C6—H6	0.9300
N3—O2—N1	112.6 (2)	H8A—C8—H8B	107.7
C1—N1—O2	104.0 (2)	C10—C9—C8	114.5 (3)
C3—N3—O2	105.7 (2)	C10—C9—H9A	108.6
C4—N4—C8	120.3 (3)	C8—C9—H9A	108.6
C4—N4—C13	122.7 (3)	C10—C9—H9B	108.6
C8—N4—C13	117.0 (3)	C8—C9—H9B	108.6
O4—N5—O3	123.4 (3)	H9A—C9—H9B	107.6
O4—N5—C7	118.1 (3)	C11—C10—C9	114.9 (3)
O3—N5—C7	118.5 (3)	C11—C10—H10A	108.6
N1—C1—C7	131.2 (3)	C9—C10—H10A	108.6
N1—C1—C3	109.3 (3)	C11—C10—H10B	108.6
C7—C1—C3	119.4 (3)	C9—C10—H10B	108.6
N3—C3—C4	129.1 (3)	H10A—C10—H10B	107.5
N3—C3—C1	108.3 (3)	C10—C11—C12	113.9 (3)
C4—C3—C1	122.5 (3)	C10—C11—H11A	108.8
N4—C4—C5	122.9 (3)	C12—C11—H11A	108.8
N4—C4—C3	122.7 (3)	C10—C11—H11B	108.8
C5—C4—C3	114.3 (3)	C12—C11—H11B	108.8
C6—C5—C4	122.9 (3)	H11A—C11—H11B	107.7
C6—C5—H5	118.6	C13—C12—C11	116.0 (3)
C4—C5—H5	118.6	C13—C12—H12A	108.3
C7—C6—C5	123.6 (3)	C11—C12—H12A	108.3
C7—C6—H6	118.2	C13—C12—H12B	108.3
C5—C6—H6	118.2	C11—C12—H12B	108.3
C6—C7—C1	117.4 (3)	H12A—C12—H12B	107.4
C6—C7—N5	121.5 (3)	N4—C13—C12	114.6 (3)
C1—C7—N5	121.1 (3)	N4—C13—H13A	108.6
N4—C8—C9	113.4 (3)	C12—C13—H13A	108.6
N4—C8—H8A	108.9	N4—C13—H13B	108.6
C9—C8—H8A	108.9	C12—C13—H13B	108.6
N4—C8—H8B	108.9	H13A—C13—H13B	107.6
C9—C8—H8B	108.9
N3—O2—N1—C1	−0.2 (4)	C4—C5—C6—C7	−0.6 (5)
N1—O2—N3—C3	0.1 (4)	C5—C6—C7—C1	0.7 (5)
O2—N1—C1—C7	−178.6 (3)	C5—C6—C7—N5	179.7 (3)
O2—N1—C1—C3	0.3 (3)	N1—C1—C7—C6	177.8 (3)
O2—N3—C3—C4	177.5 (3)	C3—C1—C7—C6	−1.0 (4)
O2—N3—C3—C1	0.1 (3)	N1—C1—C7—N5	−1.1 (5)
N1—C1—C3—N3	−0.3 (4)	C3—C1—C7—N5	−179.9 (3)
C7—C1—C3—N3	178.8 (3)	O4—N5—C7—C6	178.5 (3)
N1—C1—C3—C4	−177.9 (3)	O3—N5—C7—C6	−0.7 (5)
C7—C1—C3—C4	1.1 (4)	O4—N5—C7—C1	−2.6 (5)
C8—N4—C4—C5	10.9 (5)	O3—N5—C7—C1	178.2 (3)
C13—N4—C4—C5	−169.9 (3)	C4—N4—C8—C9	−93.0 (4)
C8—N4—C4—C3	−165.7 (3)	C13—N4—C8—C9	87.8 (4)
C13—N4—C4—C3	13.4 (5)	N4—C8—C9—C10	−76.2 (4)
N3—C3—C4—N4	−1.1 (5)	C8—C9—C10—C11	52.7 (5)
C1—C3—C4—N4	176.0 (3)	C9—C10—C11—C12	−65.6 (5)
N3—C3—C4—C5	−178.0 (3)	C10—C11—C12—C13	87.6 (4)
C1—C3—C4—C5	−0.9 (4)	C4—N4—C13—C12	150.0 (3)
N4—C4—C5—C6	−176.3 (3)	C8—N4—C13—C12	−30.8 (4)
C3—C4—C5—C6	0.6 (5)	C11—C12—C13—N4	−47.6 (5)