Isomeric nitro­phthal­imides: sheets built from N—H⋯O and C—H⋯O hydrogen bonds

Glidewell, C.; Low, J.N.; Skakle, J.M.S.; Wardell, J.L.

doi:10.1107/S0108270104026137

organic compounds

STRUCTURAL
CHEMISTRY

ISSN: 2053-2296

Volume 60| Part 12| December 2004| Pages o872-o875

doi:10.1107/S0108270104026137

Isomeric nitrophthalimides: sheets built from N—H⋯O and C—H⋯O hydrogen bonds

Christopher Glidewell,^a ^* John N. Low,^b Janet M. S. Skakle ^b and James L. Wardell ^c

^aSchool of Chemistry, University of St Andrews, Fife KY16 9ST, Scotland, ^bDepartment of Chemistry, University of Aberdeen, Meston Walk, Old Aberdeen AB24 3UE, Scotland, and ^cInstituto de Química, Departamento de Química Inorgânica, Universidade Federal do Rio de Janeiro, 21945-970 Rio de Janeiro, RJ, Brazil
^*Correspondence e-mail: cg@st-andrews.ac.uk

(Received 11 October 2004; accepted 14 October 2004; online 11 November 2004)

Molecules of 3-nitrophthalimide, C₈H₄N₂O₄, are linked into sheets by a combination of one N—H⋯O hydrogen bond [H⋯O = 1.99 Å, N⋯O = 2.8043 (14) Å and N—H⋯O = 176°] and two independent C—H⋯O hydrogen bonds [H⋯O = 2.36 and 2.56 Å, C⋯O = 3.1639 (16) and 3.4386 (16) Å, and C—H⋯O = 142 and 153°], and these sheets are linked into pairs by a single π–π stacking interaction. Molecules of isomeric 4-nitrophthalimide are linked into sheets by a combination of one three-centre N—H⋯(O)₂ hydrogen bond [H⋯O = 2.14 and 2.55 Å, N⋯O = 2.974 (3) and 3.231 (3) Å, N—H⋯O = 151 and 131°, and O⋯H⋯O = 76°] and two independent two-centre C—H⋯O hydrogen bonds [H⋯O = 2.38 and 2.54 Å, C⋯O = 3.257 (4) and 3.452 (4) Å, and C—H⋯O = 156 and 168°].

Comment

The isomeric title compounds 3-nitrophthalimide, (I), and 4-nitrophthalimide, (II), contain, within very compact molecules, a wide variety of potential hydrogen-bond donors and acceptors (Fig. 1). Both N—H and C—H bonds provide potential donors, while carbonyl and nitro O atoms and the arene ring all provide potential acceptors, although there is a

significant excess of hard acceptors over hard donors (Braga et al., 1995

; Desiraju & Steiner, 1999

). In addition, aromatic π–π stacking interactions and non-bonded dipolar interactions (Allen et al., 1998

) involving both carbonyl and nitro groups are possible, in principle.

In the event, the supramolecular structure of (I) (Fig. 1) is dominated by a two-centre N—H⋯O hydrogen bond, in which the acceptor is a carbonyl O atom, and two independent C—H⋯O hydrogen bonds, one involving a carbonyl O atom and the other a nitro O atom as acceptor. By contrast, the supramolecular structure of (II) (Fig. 2) is dominated by one asymmetric three-centre N—H⋯(O)₂ hydrogen bond, involving both of the carbonyl O atoms as the acceptors, and two independent two-centre C—H⋯O hydrogen bonds, one involving a carbonyl O atom and the other a nitro O atom as acceptor.

In isomer (I), each of the independent hydrogen bonds (Table 1) can be regarded as producing a one-dimensional substructure (Gregson et al., 2000 ), all parallel to the [100] direction but all generated by different symmetry operations; the combination of these three motifs generates a sheet. The formation of the sheets in (I) is most readily analysed by considering, in turn, the action of each hydrogen bond. Amine atom N1 in the molecule at (x, y, z) acts as a hydrogen-bond donor to carbonyl atom O1 in the molecule at ( $[1 \over 2]$ + x, y, $[1 \over 2]$ − z), so producing a C(4) chain running parallel to the [100] direction and generated by the a-glide plane at z = $[1 \over 4]$ (Fig. 3).

At the same time, aryl atom C6 in the molecule at (x, y, z) acts as a hydrogen-bond donor to the second carbonyl O atom, O2, in the molecule at (−1 + x, y, z), thus generating by translation a C(7) chain along [100]. The combination of the two motifs having carbonyl acceptors generates a column of R₃²(14) rings across z = $[1\over4]$ (Fig. 3). Finally, aryl atom C5 at (x, y, z) acts as a hydrogen-bond donor to nitro atom O41 in the molecule at (− $[1\over2]$ + x, y, $[3 \over 2]$ − z), so forming a C(5) chain along [100], this time generated by the a-glide plane at z = $[3 \over 4]$ . The combination of the two motifs involving aryl H atoms generates a column of R₃³(15) rings across z = $[3 \over 4]$ (Fig. 3). Neither of the rings utilizes all three independent hydrogen bonds. However, the combination of all three hydrogen bonds generates a (010) sheet in which columns of R₃³(14) rings across z = n + $[1\over4]$ (n = zero or integer) alternate with columns of R₃³(15) rings across z = n + $[3 \over 4]$ (n = zero or integer) (Fig. 3). Four sheets of this type pass through each unit cell, and the sheets are linked weakly into pairs by a single aromatic π–π stacking interaction.

The C3–C8 aryl rings in the molecules at (x, y, z) and (−x, −y, 1 − z) are strictly parallel, with an interplanar spacing of 3.309 (2) Å; the ring-centroid separation is 3.758 (2) Å, corresponding to a centroid offset of 1.781 (2) Å (Fig. 4). These two molecules lie in the (010) sheets within the domains 0.02 < y < 0.31 and −0.21 < y < −0.02, respectively, and these two sheets are thus linked into a bilayer. The formation of the bilayer is reinforced by a dipolar interaction between the negatively polarized nitro atom O42 in the molecule at (x, y, z) and the positively polarized carbonyl atom C1 in the molecule at ( $[1\over2]$ − x, −y, $[1\over2]$ + z), which forms part of the sheet in the domain −0.21 < y < −0.02. The C⋯Oⁱ distance [symmetry code: (i) $[1\over2]$ − x, −y, $[1\over2]$ + z] is 2.980 (2) Å and the C⋯Oⁱ—Nⁱ angle is 135.9 (2)°. However, there are no direction-specific interactions between adjacent bilayers

In isomer (II), the hard and soft hydrogen bonds independently generate two one-dimensional substructures, each in the form of a chain of rings, and these chains combine to form sheets. Amine atom N1 in the molecule of (II) at (x, y, z) acts as a hydrogen-bond donor to carbonyl atoms O1 and O2 in the molecules at (2 − x, − $[1\over2]$ + y, $[3 \over2]$ − z) and (2 − x, $[1\over2]$ + y, $[3\over2]$ − z), respectively. These two interactions (Table 2) are the strong and weak components of a markedly asymmetric, but essentially planar, three-centre interaction. The sum of the angles at atom H1 is 358°. Together these interactions produce a chain of edge-fused R₂²(8) rings running parallel to the [010] direction and generated by the 2₁ screw axis along (1, y, $[3 \over 4]$ ) (Fig. 5).

In addition, aryl atoms C4 and C7 in the molecule at (x, y, z) act as donors, respectively, to atoms O1 and O51 in the molecules at (−1 + x, −1 + y, z) and (1 + x, 1 + y, z), so generating two individual C(6) chains, whose combined action generates by translation a C(6)C(6)[R₂²(10)] chain of rings (Bernstein et al., 1995 ) running parallel to the [110] direction (Fig. 6). The combination of the [010] and [110] chains generates a (001) sheet, which is modestly reinforced by a dipolar interaction between the negatively polarized atom O2 at (x, y, z) and the positively polarized atom C2 at (1 − x, − $[1\over2]$ + y, $[3\over2]$ − z). The O2⋯C2ⁱⁱ distance is 2.906 (3) Å [symmetry code: (ii) 1 − x, − $[1\over2]$ + y, $[3\over2]$ − z] and the C2—O2⋯C2ⁱⁱ angle is 156.1 (2)°, indicating an interaction whose geometry is intermediate between the perpendicular motif I and the sheared motif III described by Allen et al. (1998). The two molecules involved in this interaction lie in the [010] chains along (1, y, $[3 \over4]$ ) and ( $[1\over2]$ , y, $[3 \over4]$ ), so that this dipolar interaction generates a motif along [100] within the (010) sheet. There are no direction-specific interactions between adjacent sheets.

The bond distances and angles within the molecules of (I) and (II) present no unusual values. The dihedral angle between the planes of the aryl ring and the nitro group is 31.6 (2)° in (I) and 8.0 (2)° in (II), so that each molecule has point group C₁; this is sufficient to render the molecules of both isomers chiral. Isomer (I) crystallizes in the centrosymmetric space group Pbca, as a racemate with equal numbers of both conformational enantiomers present in each single-crystal domain. Isomer (II) crystallizes in space group P2₁2₁2₁ as a fully ordered structure, having only one conformational enantiomer present in each single-crystal domain.

Figure 1
The molecule of isomer (I

), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level.

Figure 2
The molecule of isomer (II

), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level.

Figure 3
A stereoview of part of the crystal structure of isomer (I

), showing the formation of a (010) sheet containing alternating columns of R₃³(14) and R₃³(15) rings.

Figure 4
Part of the crystal structure of isomer (I

), showing the π–π stacking interaction that links the (010) sheets into pairs. For clarity, H atoms have been omitted. Atoms marked with an asterisk (*) are at the symmetry position (−x, −y, 1 − z).

Figure 5
Part of the crystal structure of isomer (II

), showing the formation of a chain of edge-fused rings along [010]. For clarity, H atoms bonded to C atoms have been omitted. Atoms marked with an asterisk (*), a hash (#), a dollar sign ($) or an ampersand (&) are at the symmetry positions (2 − x, $[1\over2]$ + y, $[3\over2]$ − z), (2 − x, − $[1\over2]$ + y, $[3\over2]$ − z), (x, −1 + y, z) and (x, 1 + y, z), respectively.

Figure 6
Part of the crystal structure of isomer (II

), showing the formation of a chain of rings along [110]. Atoms marked with an asterisk (*) or a hash (#) are in the molecules at (1 + x, 1 + y, z) and (−1 + x, −1 + y, z), respectively.

Experimental

Commercial samples of 3- and 4-nitrophthalimide were obtained from Aldrich, and crystals suitable for single-crystal X-ray diffraction were grown from solutions in ethyl acetate [for (I)] and acetone [for (II)].

Compound (I)

Crystal data

C₈H₄N₂O₄
M_r = 192.13
Orthorhombic, Pbca
a = 8.2208 (2) Å
b = 13.0786 (4) Å
c = 13.9233 (4) Å
V = 1496.99 (7) Å³
Z = 8
D_x = 1.705 Mg m⁻³
Mo Kα radiation
Cell parameters from 1703 reflections
θ = 3.1–27.5°
μ = 0.14 mm⁻¹
T = 120 (2) K
Plate, colourless
0.48 × 0.32 × 0.08 mm

Data collection

Nonius KappaCCD diffractometer
φ and ω scans
Absorption correction: multi-scan (SADABS; Sheldrick, 2003 ) T_min = 0.954, T_max = 0.989
19 573 measured reflections
1703 independent reflections
1488 reflections with I > 2σ(I)
R_int = 0.037
θ_max = 27.5°
h = −10 → 10
k = −16 → 15
l = −18 → 16

Refinement

Refinement on F²
R[F² > 2σ(F²)] = 0.039
wR(F²) = 0.099
S = 1.10
1703 reflections
129 parameters
H-atom parameters constrained
w = 1/[σ²(F_o²) + (0.0527P)² + 0.5962P] where P = (F_o² + 2F_c²)/3
(Δ/σ)_max < 0.001
Δρ_max = 0.33 e Å⁻³
Δρ_min = −0.42 e Å⁻³
Extinction correction: SHELXL97
Extinction coefficient: 0.033 (4)

Table 1
Hydrogen-bonding geometry (Å, °) for (I)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1⋯O1ⁱⁱⁱ	0.82	1.99	2.8043 (14)	176
C5—H5⋯O41^iv	0.95	2.56	3.4386 (16)	153
C6—H6⋯O2^v	0.95	2.36	3.1639 (16)	142
Symmetry codes: (iii) $[{\script{1\over 2}}+x,y,{\script{1\over 2}}-z]$ ; (iv) $[x-{\script{1\over 2}},y,{\script{3\over 2}}-z]$ ; (v) x-1,y,z.

Compound (II)

Crystal data

C₈H₄N₂O₄
M_r = 192.13
Orthorhombic, P2₁2₁2₁
a = 5.3114 (3) Å
b = 5.6812 (5) Å
c = 24.645 (2) Å
V = 743.67 (10) Å³
Z = 4
D_x = 1.716 Mg m⁻³
Mo Kα radiation
Cell parameters from 1007 reflections
θ = 3.3–27.5°
μ = 0.14 mm⁻¹
T = 291 (2) K
Plate, colourless
0.26 × 0.22 × 0.04 mm

Data collection

Nonius KappaCCD diffractometer
φ scans, and ω scans with κ offsets
Absorption correction: multi-scan (SORTAV; Blessing, 1995 , 1997 ) T_min = 0.956, T_max = 0.994
6348 measured reflections
1007 independent reflections
804 reflections with I > 2σ(I)
R_int = 0.060
θ_max = 27.5°
h = −6 → 6
k = −7 → 7
l = −31 → 31

Refinement

Refinement on F²
R[F² > 2σ(F²)] = 0.043
wR(F²) = 0.110
S = 1.03
1007 reflections
127 parameters
H-atom parameters constrained
w = 1/[σ²(F_o²) + (0.0707P)² + 0.0553P] where P = (F_o² + 2F_c²)/3
(Δ/σ)_max < 0.001
Δρ_max = 0.26 e Å⁻³
Δρ_min = −0.27 e Å⁻³

Table 2
Hydrogen-bonding geometry (Å, °) for (II)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1⋯O2^vi	0.92	2.55	3.231 (3)	131
N1—H1⋯O1^vii	0.92	2.14	2.974 (3)	151
C4—H4⋯O1^viii	0.93	2.54	3.452 (4)	168
C7—H7⋯O51^ix	0.93	2.38	3.257 (4)	156
Symmetry codes: (vi) $[2-x,{\script{1\over 2}}+y,{\script{3\over 2}}-z]$ ; (vii) $[2-x,y-{\script{1\over 2}},{\script{3\over 2}}-z]$ ; (viii) x-1,y-1,z; (ix) 1+x,1+y,z.

Space group Pbca for (I) and P2₁2₁2₁ for (II) were uniquely assigned from the systematic absences. All H atoms were located from difference maps and then treated as riding atoms, with C—H distances of 0.95 Å and N—H distances of 0.82 Å in (I) at 120 (2) K, and C—H distances of 0.93 Å and N—H distances of 0.92 Å in (II) at 291 (2) K, and with U_iso(H) values of 1.2U_eq(C,N). In the absence of any significant anomalous scattering, the Flack (1983 ) parameter for isomer (II) was indeterminate (Flack & Bernardinelli, 2000 ), and it was not possible to establish the absolute configuration (Jones, 1986 ). Accordingly, the Friedel equivalent reflections were merged prior to the final refinements.

For compound (I), data collection: COLLECT (Hooft, 1999 ); cell refinement: DENZO (Otwinowski & Minor, 1997 ) and COLLECT; data reduction: DENZO and COLLECT. For compound (II), data collection: KappaCCD Server Software (Nonius, 1997 ); cell refinement: DENZO–SMN (Otwinowski & Minor, 1997); data reduction: DENZO–SMN. For both compounds, program(s) used to solve structure: OSCAIL (McArdle, 2003 ) and SHELXS97 (Sheldrick, 1997 ); program(s) used to refine structure: OSCAIL and SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 2003 ); software used to prepare material for publication: SHELXL97 and PRPKAPPA (Ferguson, 1999 ).

Supporting information

Crystal structure: contains datablocks global, I, II. DOI: 10.1107/S0108270104026137/sk1783sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S0108270104026137/sk1783Isup2.hkl

Structure factors: contains datablock II. DOI: 10.1107/S0108270104026137/sk1783IIsup3.hkl

Comment top

The isomeric compounds 3-nitrophthalimide, (I), and 4-nitrophthalimide, (II), contain, within very compact molecules, a wide variety of potential hydrogen-bond donors and acceptors (Fig. 1). Both N—H and C—H bonds provide potential donors, while carbonyl O and nitro O atoms and the arene ring all provide potential acceptors, although there is a significant excess of hard (Braga et al., 1995; Desiraju & Steiner, 1999) acceptors over hard donors. In addition, aromatic π–π stacking interactions and non-bonded dipolar interactions (Allen et al., 1998) involving both carbonyl and nitro groups are possible in principle.

In the event, the supramolecular structure of (I) (Fig. 1) is dominated by a two-centre N—H···O hydrogen bond, in which the acceptor is a carbonyl O atom, and two independent C—H···O hydrogen bonds, one involving a carbonyl O and the other a nitro O atom as acceptor. By contrast, the supramolecular structure of (II) (Fig. 2) is dominated by one rather asymmetric three-centre N—H···(O)₂ hydrogen bond, involving both of the carbonyl O atoms as the acceptors, and two independent two-centre C—H···O hydrogen bonds, one involving a carbonyl O and the other a nitro O atom as acceptor.

In isomer (I), each of the independent hydrogen bonds (Table 1) can be regarded as producing a one-dimensional sub-structure (Gregson et al., 2000), all parallel to the [100] direction but all generated by different symmetry operations; the combination of these three motifs generates a sheet. The formation of the sheets in (I) is most readily analysed by considering in turn the action of each hydrogen bond. Amine atom N1 in the molecule at (x, y, z) acts as a hydrogen-bond donor to carbonyl atom O1 in the molecule at (0.5 + x, y, 0.5 − z), so producing a C(4) chain running parallel to the [100] direction and generated by the a-glide plane at z = 0.25 (Fig. 3).

At the same time, aryl atom C6 in the molecule at (x, y, z) acts as a hydrogen-bond donor to the second carbonyl O atom, O2, in the molecule at (−1 + x, y, z), thus generating by translation a C(7) chain along [100]; the combination of the two motifs having carbonyl acceptors generates a column of R³₃(14) rings across z = 0.25 (Fig. 3). Finally, aryl atom C5 at (x, y, z) acts as a hydrogen-bond donor to nitro atom O41 in the molecule at (−0.5 + x, y, 1.5 − z), so forming a C(5) chain along [100], this time generated by the a-glide plane at z = 0.75; the combination of the two motifs involving aryl H atoms generates a column of R³₃(15) rings across z = 0.75 (Fig. 3). Neither of the rings utilizes all three independent hydrogen bonds. However, the combination of all three hydrogen bonds generates a (010) sheet in which columns of R³₃(14) rings across z = n + 0.25 (n = zero or integer) alternate with columns of R³₃(15) rings across z = n + 0.75 (n = zero or integer) (Fig. 3). Four sheets of this type pass through each unit cell, and the sheets are weakly linked into pairs by a single aromatic π–π stacking interaction.

The C3–C8 aryl rings in the molecules at (x, y, z) and (-x, −y, 1 − z) are strictly parallel, with an interplanar spacing of 3.309 (2) Å; the ring-centroid separation is 3.758 (2) Å, corresponding to a centroid offset of 1.781 (2) Å (Fig. 4). These two molecules lie in the (010) sheets within the domains 0.02 < y < 0.31 and −0.21 < y < −0.02, respectively, and these two sheets are thus linked into a bilayer. The formation of the bilayer is reinforced by a dipolar interaction between the negatively polarized nitro atom O42 in the molecule at (x, y, z) and the positively polarized carbonyl atom C1 in the molecule at (0.5 − x, −y, 0.5 + z), which forms part of the sheet in the domain −0.21 < y < −0.02. The C···Oⁱ distance [symmetry code: (i) 0.5 − x, −y, 0.5 + z] is 2.980 (2) Å and the C···Oⁱ—Nⁱ angle is 135.9 (2)°. However, there are no direction-specific interactions between adjacent bilayers

In isomer (II), the hard and soft hydrogen bonds independently generate two one-dimensional sub-structures, each in the form of a chain of rings, and these chains combine to form sheets. Amine atom N1 in the molecule of (II) at (x, y, z) acts as a hydrogen-bond donor to carbonyl atoms O1 and O2 in the molecules at (2 − x, −0.5 + y, 1.5 − z) and (2 − x, 0.5 + y, 1.5 − z), respectively. These two interactions (Table 2) are the strong and weak components of a markedly-asymmetric, but essentially planar, three-centre interaction. The sum of the angles at atom H1 is 358°. Together these interactions produce a chain of edge-fused R²₂(8) rings running parallel to the [010] direction and generated by the 2₁ screw axis along (1, y, 3/4) (Fig. 5).

In addition, aryl atoms C4 and C7 in the molecule at (x, y, z) act as donors, respectively, to atoms O1 and O51 in the molecules at (−1 + x, −1 + y, z) and (1 + x, 1 + y, z), so generating two individual C(6) chains, whose combined action generates by translation a C(6) C(6)[R²₂(10)] chain of rings (Bernstein et al., 1995) running parallel to the [110] direction (Fig. 6). The combination of the [010] and [110] chains generates a (001) sheet, which is modestly reinforced by a dipolar interaction between the negatively polarized atom O2 at (x, y, z) and the positively polarized atom C2 at (1 − x, −0.5 + y, 1.5 − z). The O2···C2ⁱⁱ distance is 2.906 (3) Å [symmetry code: (ii) 1 − x, −0.5 + y, 1.5 − z] and the C2—O2···C2ⁱⁱ angle is 156.1 (2)°, indicating an interaction whose geometry is intermediate between the perpendicular motif (I) and the sheared motif (III) described by Allen et al. (1998). The two molecules involved in this interaction lie in the [010] chains along (1, y, 3/4) and (1/2, y, 3/4), so that this dipolar interaction generates a motif along [100] within the (010) sheet. There are no direction-specific interactions between adjacent sheets.

The bond distances and angles within the molecules of (I) and (II) present no unusual values. The dihedral angle between the planes of the aryl ring and the nitro group is 31.6 (2)° in (I) and 8.0 (2)° in (II), so that each molecule has point group C₁; this is sufficient to render the molecules of both isomers chiral. Isomer (I) crystallizes in the centrosymmetric space group Pbca, as a racemate with equal numbers of both conformational enantiomers present in each single-crystal domain. Isomer (II) crystallizes in space group P2₁2₁2₁ as a fully ordered structure, having only one conformational enantiomer present in each single-crystal domain.

Experimental top

Commercial samples of 3- and 4-nitrophthalimide (obtained from Aldrich) and crystals suitable for single-crystal X-ray diffraction were grown from solutions in ethyl acetate, for (I), and acetone, for (II).

Computing details top

Data collection: COLLECT (Hooft, 1999) for (I); KappaCCD Server Software (Nonius, 1997) for (II). Cell refinement: DENZO (Otwinowski & Minor, 1997) and COLLECT for (I); DENZO–SMN (Otwinowski & Minor, 1997) for (II). Data reduction: DENZO and COLLECT for (I); DENZO–SMN for (II). For both compounds, program(s) used to solve structure: OSCAIL (McArdle, 2003) and SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: OSCAIL and SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 2003); software used to prepare material for publication: SHELXL97 and PRPKAPPA (Ferguson, 1999).

Figures top

	Fig. 1. The molecule of isomer (I), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level.
	Fig. 2. The molecule of isomer (II), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level.
	Fig. 3. A stereoview of part of the crystal structure of isomer (I), showing the formation of a (010) sheet containing alternating columns of R³₃(14) and R³₃(15) rings.
	Fig. 4. Part of the crystal structure of isomer (I), showing the π–π stacking interaction that links the (010) sheets into pairs. For clarity, H atoms have been omitted. Atoms marked with an asterisk (*) are at the symmetry position (-x, −y, 1 − z).
	Fig. 5. Part of the crystal structure of isomer (II), showing the formation of a chain of edge-fused rings along [010]. For clarity, H atoms bonded to C atoms have been omitted. Atoms marked with an asterisk (*), a hash (#), a dollar sign () or an ampersand (&) are at the symmetry positions (2 − x, 0.5 + y, 1.5 − z), (2 − x, −0.5 + y, 1.5 − z), (x, −1 + y, z) and (x, 1 + y, z), respectively.
	Fig. 6. Part of the crystal structure of isomer (II), showing the formation of a chain of rings along [110]. Atoms marked with an asterisk (*) or a hash (#) are in the molecules at (1 + x, 1 + y, z) and (−1 + x, −1 + y, z), respectively.

(I) 3-Nitrophthalimide top

Crystal data top

C₈H₄N₂O₄	F(000) = 784
M_r = 192.13	D_x = 1.705 Mg m⁻³
Orthorhombic, Pbca	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2ab	Cell parameters from 1703 reflections
a = 8.2208 (2) Å	θ = 3.1–27.5°
b = 13.0786 (4) Å	µ = 0.14 mm⁻¹
c = 13.9233 (4) Å	T = 120 K
V = 1496.99 (7) Å³	Plate, colourless
Z = 8	0.48 × 0.32 × 0.08 mm

Data collection top

Bruker-Nonius 95mm CCD camera on κ-goniostat diffractometer	1703 independent reflections
Radiation source: Bruker–Nonius FR591 rotating anode	1488 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.037
Detector resolution: 9.091 pixels mm^-1	θ_max = 27.5°, θ_min = 3.1°
ϕ & ω scans	h = −10→10
Absorption correction: multi-scan (SADABS; Sheldrick, 2003)	k = −16→15
T_min = 0.954, T_max = 0.989	l = −18→16
19573 measured reflections

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)] = 0.039	H-atom parameters constrained
wR(F²) = 0.099	w = 1/[σ²(F_o²) + (0.0527P)² + 0.5962P] where P = (F_o² + 2F_c²)/3
S = 1.10	(Δ/σ)_max < 0.001
1703 reflections	Δρ_max = 0.33 e Å⁻³
129 parameters	Δρ_min = −0.42 e Å⁻³
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.033 (4)

Crystal data top

C₈H₄N₂O₄	V = 1496.99 (7) Å³
M_r = 192.13	Z = 8
Orthorhombic, Pbca	Mo Kα radiation
a = 8.2208 (2) Å	µ = 0.14 mm⁻¹
b = 13.0786 (4) Å	T = 120 K
c = 13.9233 (4) Å	0.48 × 0.32 × 0.08 mm

Data collection top

Bruker-Nonius 95mm CCD camera on κ-goniostat diffractometer	1703 independent reflections
Absorption correction: multi-scan (SADABS; Sheldrick, 2003)	1488 reflections with I > 2σ(I)
T_min = 0.954, T_max = 0.989	R_int = 0.037
19573 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.039	0 restraints
wR(F²) = 0.099	H-atom parameters constrained
S = 1.10	Δρ_max = 0.33 e Å⁻³
1703 reflections	Δρ_min = −0.42 e Å⁻³
129 parameters

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
N1	0.41423 (13)	0.16003 (9)	0.34763 (7)	0.0189 (3)
C1	0.25286 (16)	0.17714 (9)	0.32887 (8)	0.0172 (3)
O1	0.19836 (10)	0.20978 (7)	0.25357 (6)	0.0209 (2)
C2	0.44360 (15)	0.12650 (10)	0.44109 (9)	0.0173 (3)
O2	0.57573 (11)	0.10362 (7)	0.47130 (7)	0.0229 (3)
C3	0.27874 (15)	0.12461 (9)	0.48828 (9)	0.0162 (3)
C4	0.22350 (15)	0.10039 (9)	0.57975 (9)	0.0169 (3)
C5	0.05837 (16)	0.09960 (9)	0.59990 (9)	0.0190 (3)
C6	−0.05338 (16)	0.12442 (10)	0.52875 (9)	0.0194 (3)
C7	−0.00199 (15)	0.15097 (9)	0.43675 (9)	0.0180 (3)
C8	0.16350 (15)	0.15055 (9)	0.41884 (8)	0.0160 (3)
N4	0.33533 (14)	0.07751 (8)	0.65906 (7)	0.0202 (3)
O41	0.46763 (13)	0.12029 (8)	0.65980 (7)	0.0284 (3)
O42	0.28788 (13)	0.01824 (8)	0.72135 (7)	0.0292 (3)
H1	0.4950	0.1735	0.3159	0.037 (5)*
H5	0.0216	0.0821	0.6624	0.023*
H6	−0.1664	0.1233	0.5431	0.023*
H7	−0.0779	0.1687	0.3881	0.022*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
N1	0.0147 (5)	0.0266 (6)	0.0154 (5)	−0.0013 (4)	0.0017 (4)	−0.0002 (4)
C1	0.0178 (6)	0.0167 (6)	0.0170 (6)	−0.0011 (5)	−0.0009 (5)	−0.0031 (5)
O1	0.0220 (5)	0.0258 (5)	0.0151 (4)	−0.0011 (4)	−0.0029 (3)	0.0018 (4)
C2	0.0163 (6)	0.0188 (6)	0.0167 (6)	−0.0005 (5)	0.0000 (5)	−0.0034 (5)
O2	0.0161 (5)	0.0294 (5)	0.0233 (5)	0.0022 (4)	−0.0028 (4)	−0.0004 (4)
C3	0.0159 (6)	0.0165 (6)	0.0163 (6)	0.0001 (5)	−0.0004 (5)	−0.0014 (5)
C4	0.0183 (6)	0.0173 (6)	0.0152 (6)	0.0002 (5)	−0.0025 (5)	−0.0006 (5)
C5	0.0211 (7)	0.0186 (6)	0.0173 (6)	−0.0008 (5)	0.0033 (5)	−0.0018 (5)
C6	0.0169 (6)	0.0197 (6)	0.0214 (6)	0.0000 (5)	0.0015 (5)	−0.0034 (5)
C7	0.0166 (6)	0.0179 (6)	0.0196 (6)	0.0009 (5)	−0.0023 (5)	−0.0019 (5)
C8	0.0171 (6)	0.0158 (6)	0.0151 (6)	0.0000 (4)	−0.0008 (5)	−0.0014 (4)
N4	0.0223 (6)	0.0224 (6)	0.0159 (5)	0.0020 (5)	−0.0023 (4)	−0.0002 (4)
O41	0.0241 (5)	0.0382 (6)	0.0230 (5)	−0.0062 (4)	−0.0080 (4)	0.0028 (4)
O42	0.0335 (6)	0.0331 (6)	0.0210 (5)	−0.0007 (4)	−0.0009 (4)	0.0104 (4)

Geometric parameters (Å, º) top

N1—C1	1.3705 (16)	C4—N4	1.4678 (15)
N1—C2	1.3943 (16)	C5—C6	1.3895 (19)
N1—H1	0.8167	C5—H5	0.95
C1—O1	1.2174 (15)	C6—C7	1.3928 (18)
C1—C8	1.4933 (16)	C6—H6	0.95
C2—O2	1.2026 (15)	C7—C8	1.3832 (17)
C2—C3	1.5063 (17)	C7—H7	0.95
C3—C4	1.3887 (17)	N4—O41	1.2231 (15)
C3—C8	1.3954 (17)	N4—O42	1.2269 (14)
C4—C5	1.3862 (17)

C1—N1—C2	113.38 (10)	C4—C5—C6	120.09 (12)
C1—N1—H1	130.4	C4—C5—H5	120.0
C2—N1—H1	115.6	C6—C5—H5	120.0
O1—C1—N1	125.29 (12)	C5—C6—C7	120.89 (12)
O1—C1—C8	128.54 (12)	C5—C6—H6	119.6
N1—C1—C8	106.16 (10)	C7—C6—H6	119.6
O2—C2—N1	124.13 (12)	C8—C7—C6	117.59 (11)
O2—C2—C3	131.00 (12)	C8—C7—H7	121.2
N1—C2—C3	104.86 (10)	C6—C7—H7	121.2
C4—C3—C8	117.96 (11)	C7—C8—C3	122.95 (11)
C4—C3—C2	134.26 (12)	C7—C8—C1	129.36 (11)
C8—C3—C2	107.74 (10)	C3—C8—C1	107.69 (11)
C5—C4—C3	120.51 (11)	O41—N4—O42	124.46 (11)
C5—C4—N4	117.36 (11)	O41—N4—C4	118.03 (10)
C3—C4—N4	122.12 (11)	O42—N4—C4	117.48 (11)

C2—N1—C1—O1	177.46 (12)	C5—C6—C7—C8	0.70 (18)
C2—N1—C1—C8	−1.07 (14)	C6—C7—C8—C3	0.22 (18)
C1—N1—C2—O2	177.25 (12)	C6—C7—C8—C1	−178.73 (12)
C1—N1—C2—C3	−1.49 (14)	C4—C3—C8—C7	−1.40 (18)
O2—C2—C3—C4	2.5 (2)	C2—C3—C8—C7	176.55 (11)
N1—C2—C3—C4	−178.89 (13)	C4—C3—C8—C1	177.75 (11)
O2—C2—C3—C8	−174.98 (14)	C2—C3—C8—C1	−4.30 (13)
N1—C2—C3—C8	3.63 (13)	O1—C1—C8—C7	4.0 (2)
C8—C3—C4—C5	1.68 (18)	N1—C1—C8—C7	−177.50 (12)
C2—C3—C4—C5	−175.60 (13)	O1—C1—C8—C3	−175.05 (12)
C8—C3—C4—N4	−176.64 (11)	N1—C1—C8—C3	3.42 (13)
C2—C3—C4—N4	6.1 (2)	C5—C4—N4—O41	−146.87 (12)
C3—C4—C5—C6	−0.82 (19)	C3—C4—N4—O41	31.51 (17)
N4—C4—C5—C6	177.58 (11)	C5—C4—N4—O42	31.58 (16)
C4—C5—C6—C7	−0.41 (19)	C3—C4—N4—O42	−150.05 (12)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···O1ⁱ	0.82	1.99	2.8043 (14)	176
C5—H5···O41ⁱⁱ	0.95	2.56	3.4386 (16)	153
C6—H6···O2ⁱⁱⁱ	0.95	2.36	3.1639 (16)	142

Symmetry codes: (i) x+1/2, y, −z+1/2; (ii) x−1/2, y, −z+3/2; (iii) x−1, y, z.

(II) 4-Nitrophthalimide top

Crystal data top

C₈H₄N₂O₄	F(000) = 392
M_r = 192.13	D_x = 1.716 Mg m⁻³
Orthorhombic, P2₁2₁2₁	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2ab	Cell parameters from 1007 reflections
a = 5.3114 (3) Å	θ = 3.3–27.5°
b = 5.6812 (5) Å	µ = 0.14 mm⁻¹
c = 24.645 (2) Å	T = 291 K
V = 743.67 (10) Å³	Plate, colourless
Z = 4	0.26 × 0.22 × 0.04 mm

Data collection top

Nonius KappaCCD diffractometer	1007 independent reflections
Radiation source: rotating anode	804 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.060
ϕ scans, and ω scans with κ offsets	θ_max = 27.5°, θ_min = 3.3°
Absorption correction: multi-scan (SORTAV; Blessing, 1995, 1997)	h = −6→6
T_min = 0.956, T_max = 0.994	k = −7→7
6348 measured reflections	l = −31→31

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)] = 0.043	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.110	H-atom parameters constrained
S = 1.03	w = 1/[σ²(F_o²) + (0.0707P)² + 0.0553P] where P = (F_o² + 2F_c²)/3
1007 reflections	(Δ/σ)_max < 0.001
127 parameters	Δρ_max = 0.26 e Å⁻³
0 restraints	Δρ_min = −0.27 e Å⁻³

Crystal data top

C₈H₄N₂O₄	V = 743.67 (10) Å³
M_r = 192.13	Z = 4
Orthorhombic, P2₁2₁2₁	Mo Kα radiation
a = 5.3114 (3) Å	µ = 0.14 mm⁻¹
b = 5.6812 (5) Å	T = 291 K
c = 24.645 (2) Å	0.26 × 0.22 × 0.04 mm

Data collection top

Nonius KappaCCD diffractometer	1007 independent reflections
Absorption correction: multi-scan (SORTAV; Blessing, 1995, 1997)	804 reflections with I > 2σ(I)
T_min = 0.956, T_max = 0.994	R_int = 0.060
6348 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.043	0 restraints
wR(F²) = 0.110	H-atom parameters constrained
S = 1.03	Δρ_max = 0.26 e Å⁻³
1007 reflections	Δρ_min = −0.27 e Å⁻³
127 parameters

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
N1	0.8528 (5)	0.4545 (4)	0.71294 (9)	0.0268 (6)
C1	0.8471 (6)	0.6382 (5)	0.67636 (10)	0.0242 (6)
O1	0.9844 (4)	0.8077 (4)	0.67667 (8)	0.0306 (5)
C2	0.6641 (5)	0.2892 (5)	0.70364 (11)	0.0257 (7)
O2	0.6265 (4)	0.1134 (4)	0.73007 (8)	0.0336 (6)
C3	0.5294 (5)	0.3736 (5)	0.65413 (11)	0.0236 (6)
C4	0.3286 (5)	0.2744 (5)	0.62623 (11)	0.0243 (6)
C5	0.2516 (5)	0.4022 (5)	0.58086 (10)	0.0234 (6)
N5	0.0417 (5)	0.3041 (4)	0.54841 (9)	0.0277 (6)
O51	−0.0327 (4)	0.1058 (4)	0.55967 (9)	0.0377 (6)
O52	−0.0481 (4)	0.4261 (4)	0.51226 (8)	0.0320 (5)
C6	0.3542 (6)	0.6110 (5)	0.56411 (11)	0.0251 (6)
C7	0.5546 (6)	0.7071 (6)	0.59283 (11)	0.0269 (7)
C8	0.6376 (5)	0.5839 (5)	0.63799 (11)	0.0233 (6)
H1	0.9573	0.4249	0.7418	0.032*
H4	0.2521	0.1346	0.6369	0.029*
H6	0.2904	0.6879	0.5338	0.030*
H7	0.6296	0.8477	0.5822	0.032*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
N1	0.0289 (13)	0.0261 (14)	0.0253 (12)	0.0008 (12)	−0.0031 (10)	0.0017 (10)
C1	0.0249 (14)	0.0240 (15)	0.0238 (13)	0.0020 (14)	0.0031 (11)	−0.0024 (12)
O1	0.0331 (12)	0.0290 (12)	0.0298 (10)	−0.0076 (11)	−0.0022 (9)	−0.0014 (9)
C2	0.0290 (15)	0.0209 (15)	0.0271 (13)	0.0023 (14)	0.0032 (13)	−0.0034 (12)
O2	0.0424 (14)	0.0260 (11)	0.0325 (11)	−0.0001 (11)	−0.0002 (9)	0.0038 (10)
C3	0.0233 (14)	0.0221 (15)	0.0253 (12)	0.0022 (13)	0.0015 (11)	−0.0028 (13)
C4	0.0238 (14)	0.0183 (14)	0.0309 (13)	0.0003 (13)	0.0061 (12)	−0.0011 (12)
C5	0.0192 (13)	0.0264 (16)	0.0248 (13)	0.0022 (13)	0.0009 (11)	−0.0034 (12)
N5	0.0253 (12)	0.0277 (14)	0.0300 (12)	−0.0039 (13)	0.0026 (11)	−0.0034 (12)
O51	0.0387 (12)	0.0359 (13)	0.0385 (11)	−0.0171 (12)	−0.0039 (10)	0.0030 (10)
O52	0.0309 (11)	0.0337 (13)	0.0313 (10)	0.0008 (11)	−0.0061 (9)	0.0023 (9)
C6	0.0274 (14)	0.0232 (16)	0.0246 (13)	0.0003 (14)	−0.0001 (11)	0.0009 (12)
C7	0.0286 (15)	0.0261 (16)	0.0259 (13)	−0.0014 (14)	−0.0004 (12)	−0.0005 (13)
C8	0.0219 (14)	0.0238 (16)	0.0241 (13)	−0.0004 (13)	0.0015 (11)	−0.0029 (12)

Geometric parameters (Å, º) top

N1—C1	1.379 (4)	C4—H4	0.93
N1—C2	1.392 (4)	C5—C6	1.369 (4)
N1—H1	0.92	C5—N5	1.481 (4)
C1—O1	1.208 (3)	N5—O52	1.225 (3)
C1—C8	1.493 (4)	N5—O51	1.226 (3)
C2—O2	1.209 (3)	C6—C7	1.390 (4)
C2—C3	1.494 (4)	C6—H6	0.93
C3—C8	1.384 (4)	C7—C8	1.387 (4)
C3—C4	1.388 (4)	C7—H7	0.93
C4—C5	1.395 (4)

C1—N1—C2	112.8 (2)	C6—C5—C4	125.2 (3)
C1—N1—H1	131.2	C6—C5—N5	117.6 (3)
C2—N1—H1	116.0	C4—C5—N5	117.3 (3)
O1—C1—N1	125.9 (3)	O52—N5—O51	124.0 (3)
O1—C1—C8	128.2 (3)	O52—N5—C5	118.2 (3)
N1—C1—C8	105.9 (2)	O51—N5—C5	117.8 (3)
O2—C2—N1	126.0 (3)	C5—C6—C7	119.5 (3)
O2—C2—C3	128.7 (3)	C5—C6—H6	120.3
N1—C2—C3	105.3 (2)	C7—C6—H6	120.3
C8—C3—C4	121.8 (3)	C8—C7—C6	117.0 (3)
C8—C3—C2	108.2 (3)	C8—C7—H7	121.5
C4—C3—C2	130.0 (3)	C6—C7—H7	121.5
C3—C4—C5	114.3 (3)	C3—C8—C7	122.3 (3)
C3—C4—H4	122.9	C3—C8—C1	107.8 (2)
C5—C4—H4	122.9	C7—C8—C1	129.9 (3)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···O2ⁱ	0.92	2.55	3.231 (3)	131
N1—H1···O1ⁱⁱ	0.92	2.14	2.974 (3)	151
C4—H4···O1ⁱⁱⁱ	0.93	2.54	3.452 (4)	168
C7—H7···O51^iv	0.93	2.38	3.257 (4)	156

Symmetry codes: (i) −x+2, y+1/2, −z+3/2; (ii) −x+2, y−1/2, −z+3/2; (iii) x−1, y−1, z; (iv) x+1, y+1, z.

Experimental details

	(I)	(II)
Crystal data
Chemical formula	C₈H₄N₂O₄	C₈H₄N₂O₄
M_r	192.13	192.13
Crystal system, space group	Orthorhombic, Pbca	Orthorhombic, P2₁2₁2₁
Temperature (K)	120	291
a, b, c (Å)	8.2208 (2), 13.0786 (4), 13.9233 (4)	5.3114 (3), 5.6812 (5), 24.645 (2)
V (Å³)	1496.99 (7)	743.67 (10)
Z	8	4
Radiation type	Mo Kα	Mo Kα
µ (mm⁻¹)	0.14	0.14
Crystal size (mm)	0.48 × 0.32 × 0.08	0.26 × 0.22 × 0.04

Data collection
Diffractometer	Bruker-Nonius 95mm CCD camera on κ-goniostat diffractometer	Nonius KappaCCD diffractometer
Absorption correction	Multi-scan (SADABS; Sheldrick, 2003)	Multi-scan (SORTAV; Blessing, 1995, 1997)
T_min, T_max	0.954, 0.989	0.956, 0.994
No. of measured, independent and observed [I > 2σ(I)] reflections	19573, 1703, 1488	6348, 1007, 804
R_int	0.037	0.060
(sin θ/λ)_max (Å⁻¹)	0.649	0.649

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.039, 0.099, 1.10	0.043, 0.110, 1.03
No. of reflections	1703	1007
No. of parameters	129	127
H-atom treatment	H-atom parameters constrained	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.33, −0.42	0.26, −0.27

Computer programs: COLLECT (Hooft, 1999), KappaCCD Server Software (Nonius, 1997), DENZO (Otwinowski & Minor, 1997) and COLLECT, DENZO–SMN (Otwinowski & Minor, 1997), DENZO and COLLECT, DENZO–SMN, OSCAIL (McArdle, 2003) and SHELXS97 (Sheldrick, 1997), OSCAIL and SHELXL97 (Sheldrick, 1997), PLATON (Spek, 2003), SHELXL97 and PRPKAPPA (Ferguson, 1999).

Hydrogen-bond geometry (Å, º) for (I) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···O1ⁱ	0.82	1.99	2.8043 (14)	176
C5—H5···O41ⁱⁱ	0.95	2.56	3.4386 (16)	153
C6—H6···O2ⁱⁱⁱ	0.95	2.36	3.1639 (16)	142

Symmetry codes: (i) x+1/2, y, −z+1/2; (ii) x−1/2, y, −z+3/2; (iii) x−1, y, z.

Hydrogen-bond geometry (Å, º) for (II) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···O2ⁱ	0.92	2.55	3.231 (3)	131
N1—H1···O1ⁱⁱ	0.92	2.14	2.974 (3)	151
C4—H4···O1ⁱⁱⁱ	0.93	2.54	3.452 (4)	168
C7—H7···O51^iv	0.93	2.38	3.257 (4)	156

Symmetry codes: (i) −x+2, y+1/2, −z+3/2; (ii) −x+2, y−1/2, −z+3/2; (iii) x−1, y−1, z; (iv) x+1, y+1, z.

Acknowledgements

The authors thank a referee for helpful comments on conformational enantiomerism. X-ray data were collected at the EPSRC X-ray Crystallographic Service, University of Southampton, England; the authors thank the staff for all their help and advice. JNL thanks NCR Self-Service, Dundee, for grants which have provided computing facilities for this work. JLW thanks CNPq and FAPERJ for financial support.

References

Allen, F. H., Baalham, C. A., Lommerse, J. P. M. & Raithby, P. R. (1998). Acta Cryst. B54, 320–329. Web of Science CrossRef CAS IUCr Journals Google Scholar
Bernstein, J., Davis, R. E., Shimoni, L. & Chang, N.-L. (1995). Angew. Chem. Int. Ed. Engl. 34, 1555–1573. CrossRef CAS Web of Science Google Scholar
Blessing, R. H. (1995). Acta Cryst. A51, 33–37. CrossRef CAS Web of Science IUCr Journals Google Scholar
Blessing, R. H. (1997). J. Appl. Cryst. 30, 421–426. CrossRef CAS Web of Science IUCr Journals Google Scholar
Braga, D., Grepioni, F., Birdha, K., Pedireddi, V. R. & Desiraju, G. R. (1995). J. Am. Chem. Soc. 117, 3156–3166. CrossRef CAS Web of Science Google Scholar
Desiraju, G. R. & Steiner, T. (1999). The Weak Hydrogen Bond, pp. 86–89. Oxford University Press. Google Scholar
Ferguson, G. (1999). PRPKAPPA. University of Guelph, Canada. Google Scholar
Flack, H. D. (1983). Acta Cryst. A39, 876–881. CrossRef CAS Web of Science IUCr Journals Google Scholar
Flack, H. D. & Bernardinelli, G. (2000). J. Appl. Cryst. 33, 1143–1148. Web of Science CrossRef CAS IUCr Journals Google Scholar
Gregson, R. M., Glidewell, C., Ferguson, G. & Lough, A. J. (2000). Acta Cryst. B56, 39–57. Web of Science CSD CrossRef CAS IUCr Journals Google Scholar
Hooft, R. W. W. (1999). COLLECT. Nonius BV, Delft, The Netherlands. Google Scholar
Jones, P. G. (1986). Acta Cryst. A42, 57. CrossRef Web of Science IUCr Journals Google Scholar
McArdle, P. (2003). OSCAIL for Windows. Version 10. Crystallography Centre, Chemistry Department, NUI Galway, Ireland. Google Scholar
Nonius (1997). KappaCCD Server Software. Windows 3.11 Version. Nonius BV, Delft, The Netherlands. Google Scholar
Otwinowski, Z. & Minor, W. (1997). Methods in Enzymology, Vol. 276, Macromolecular Crystallography, Part A, edited by C. W. Carter Jr & R. M. Sweet, pp. 307–326. New York: Academic Press. Google Scholar
Sheldrick, G. M. (1997). SHELXS97 and SHELXL97. University of Göttingen, Germany. Google Scholar
Sheldrick, G. M. (2003). SADABS. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Spek, A. L. (2003). J. Appl. Cryst. 36, 7–13. Web of Science CrossRef CAS IUCr Journals Google Scholar

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Volume 60| Part 12| December 2004| Pages o872-o875

doi:10.1107/S0108270104026137