2-Chloro-N-[4-chloro-2-(2-chloro­benzo­yl)phen­yl]acetamide

Dutkiewicz, G.; Siddaraju, B.P.; Yathirajan, H.S.; Narayana, B.; Kubicki, M.

doi:10.1107/S1600536810003375

2-Chloro-N-[4-chloro-2-(2-chlorobenzoyl)phenyl]acetamide

G. Dutkiewicz, B. P. Siddaraju, H. S. Yathirajan, B. Narayana and M. Kubicki

In the title compound, C₁₅H₁₀Cl₃NO₂, an intramolecular N—H

O hydrogen bond forms a six-membered ring and enforces an almost coplanar conformation for the acetamido group, the central benzene ring and the bridging carbonyl C—C(=O)—C group: the dihedral angles between the benzene ring and the acetamide and carbonyl C—C(=O)—C planes are 7.06 (11) and 7.17 (12)°, respectively. The dihedral angle between the two benzene rings is 67.43 (9)°. Because a strong hydrogen-bond donor is involved in the intramolecular interaction, the crystal packing is determined by weak C—H

O and C—H

Cl interactions.

Read article Similar articles

Supporting information

	Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536810003375/is2519sup1.cif Contains datablocks I, global
	Structure factor file (CIF format) https://doi.org/10.1107/S1600536810003375/is2519Isup2.hkl Contains datablock I

CCDC reference: 765234

checkCIF report

Key indicators

Single-crystal X-ray study
T = 295 K
Mean (C-C) = 0.004 Å
R factor = 0.043
wR factor = 0.113
Data-to-parameter ratio = 12.7

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT242_ALERT_2_C Check Low       Ueq as Compared to Neighbors for        C14
PLAT250_ALERT_2_C Large U3/U1 Ratio for Average U(i,j) Tensor ....       2.12
PLAT911_ALERT_3_C Missing # FCF Refl Between THmin & STh/L=  0.600          6
PLAT913_ALERT_3_C Missing # of Very Strong Reflections in FCF ....          3
PLAT480_ALERT_4_C Long H...A H-Bond Reported H6     ..  CL14    ..       2.87 Ang.
PLAT480_ALERT_4_C Long H...A H-Bond Reported H18    ..  CL14    ..       2.84 Ang.
PLAT912_ALERT_4_C Missing # of FCF Reflections Above STh/L=  0.600         91

   0 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
   7 ALERT level C = Check and explain
   0 ALERT level G = General alerts; check

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   2 ALERT type 2 Indicator that the structure model may be wrong or deficient
   2 ALERT type 3 Indicator that the structure quality may be low
   3 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

Comment top

Benzophenone and related compounds have been reported to act as e.g., antiallergic, anti-inflammatory, antiasthmatic, antimalarial, anti-microbial and antianaphylactic agents (Evans et al., 1987). Here we report the crystal structure of 2-chloroacetamido-5-chloro-2'-chlorobenzophenone (alternative name: 2-chloro-N-{4-chloro-2-[(2-chlorophenyl)carbonyl]phenyl}acetamide; 1, Scheme 1), which is an intermediate in the synthesis of certain anxiolytic, anticonvulsant and sedative drugs, and is also a starting material for the synthesis of diazepam and other benzodiazepines.

The structure of 1 is isostructural with the previously described 2-chloroacetamido-5-chloro-2'-fluorobenzophenone derivative (Prasanna & Guru Row, 2000). Both compounds crystallize in the triclinic P-1 space group, and the unit cell dimensions are similar. Also the positions of the atoms in the unit cell are similar, after applying the transformation (index 1 refers to Prasanna & Guru Row, 2 - to the present structure): x₂=x₁+0.5, y₂=y₁+0.5, z₂=z₁+1.5. The isostructurality index (Kálmán et al., 1991), which describes the differences between the positions of the atoms in the unit cell has the value of 97.4% (for perfect isostructurality it should be 100%). Kubicki & Szafrański (1998) proposed the modification of this latter parameter which takes into account the point group symmetry and gives more absolute measure of the degree of isostructurality: it should be 1 for ideally isomorphous compounds and 0 for randomly distributed atoms. The value of this modified index is 0.94.

The conformation of 1 (Fig. 1) might be described by dihedral angles between four approximately planar fragments: acetamide [A, planar within 0.0065 (19) Å, with Cl2 atom significantly, by 0.110 (5)Å out of the plane], central phenyl [B, maximum deviation 0.0034 (14) Å], bridging carbonyl group C—C(=O)-C [C, max. deviation 0.015 (2) Å], and terminal phenyl [D, 0.0045 (19) Å]. The first three are close to coplanarity, the dihedral angles are A/B 7.06 (11)° and B/C 7.17 (12)°. Such a coplanar conformation of phenyl and carbonyl plane is quite uncommon for benzophenones, in a majority of the compounds found in the CSD (Allen, 2002) both phenyl rings are almost equally, and significantly, twisted with respect to the central plane. In the case of 1, as in some similar cases (for instance in the isostructural 2'-fluoro derivative but also in two crystal forms of 2-chloroacetamido-5-chlorobenzophenone (monoclinic: Prasanna & Guru Row, 2000, and triclinic: Malathy Sony et al., 2005), the factor responsible for such a coplanar conformation is the intramolecular hydrogen bond N—H···O (cf. Table 1). This hydrogen bond closes the six-membered ring, planar within 0.072 (7) Å. The second phenyl ring, which has no factor that can stabilize coplanar conformation, is typically, by 62.14 (10)°, twisted with respect to the bridge. The Cl atom of chloroacetamide group is anti with respect to the oxygen atom [O10—C9—C11—Cl12 torsion angle of 176.4 (2)°] and syn with respect to the N atom [N8—C9—C11—Cl12 is -4.8 (3)°]

In the crystal structure there are some weak C—H···O and C—H···Cl interactions, which might be of some importance when the strong hydrogen bond donor is involved in intramolecular interaction (Fig. 2)

Related literature top

The title compound is isostructural with 2-chloroacetamido-5-chloro-2'-fluorobenzophenone (Prasanna & Guru Row, 2000). For the isostructurality index, see: Kálmán et al. (1991); Kubicki & Szafrański (1998). For a related structure, see: Malathy Sony et al. (2005). For the biological activity of benzophenone derivatives, see: Evans et al. (1987). For a description of the Cambridge Structural Database, see: Allen (2002).

Experimental top

The title compound was obtained as a gift sample from R. L. FineChem, Bangalore, India. The compound was used without further purification. X-ray quality crystals were obtained by slow evaporation from ethyl acetate solution (m.p. 436-438 K).

Structure description top

Computing details top

Data collection: CrysAlis PRO (Oxford Diffraction, 2009); cell refinement: CrysAlis PRO (Oxford Diffraction, 2009); data reduction: CrysAlis PRO (Oxford Diffraction, 2009); program(s) used to solve structure: SIR92 (Altomare et al., 1993); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: Stereochemical Workstation Operation Manual (Siemens, 1989); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures top

	Fig. 1. Anisotropic ellipsoid representation of the title compound together with atom labelling scheme. The ellipsoids are drawn at 50% probability level, hydrogen atoms are depicted as spheres with arbitrary radii. The intramolecular hydrogen bond is shown as a dashed line.
	Fig. 2. The crystal packing of the title compound, as seen along the a axis. Hydrogen bonds are shown as dashed lines.

2-Chloro-N-[4-chloro-2-(2-chlorobenzoyl)phenyl]acetamide top

Crystal data top

C₁₅H₁₀Cl₃NO₂	Z = 2
M_r = 342.59	F(000) = 348
Triclinic, P1	D_x = 1.558 Mg m⁻³
Hall symbol: -P 1	Cu Kα radiation, λ = 1.54178 Å
a = 7.5776 (9) Å	Cell parameters from 3832 reflections
b = 10.1565 (10) Å	θ = 4.4–75.1°
c = 10.7862 (12) Å	µ = 5.71 mm⁻¹
α = 70.069 (8)°	T = 295 K
β = 77.604 (9)°	Prism, pink
γ = 70.388 (8)°	0.35 × 0.2 × 0.2 mm
V = 730.47 (14) Å³

Data collection top

Oxford Diffraction SuperNova (single source at offset) Atlas diffractometer	2917 independent reflections
Radiation source: SuperNova (Cu) X-ray Source	2610 reflections with I > 2σ(I)
Mirror monochromator	R_int = 0.017
Detector resolution: 10.5357 pixels mm^-1	θ_max = 75.2°, θ_min = 4.4°
ω–scan	h = −9→9
Absorption correction: multi-scan (CrysAlis PRO; Oxford Diffraction, 2009)	k = −12→12
T_min = 0.117, T_max = 0.319	l = −13→13
5245 measured reflections

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) = 0.113	All H-atom parameters refined
S = 1.05	w = 1/[σ²(F_o²) + (0.0551P)² + 0.3949P] where P = (F_o² + 2F_c²)/3
2917 reflections	(Δ/σ)_max = 0.001
230 parameters	Δρ_max = 0.37 e Å⁻³
0 restraints	Δρ_min = −0.44 e Å⁻³

Crystal data top

C₁₅H₁₀Cl₃NO₂	γ = 70.388 (8)°
M_r = 342.59	V = 730.47 (14) Å³
Triclinic, P1	Z = 2
a = 7.5776 (9) Å	Cu Kα radiation
b = 10.1565 (10) Å	µ = 5.71 mm⁻¹
c = 10.7862 (12) Å	T = 295 K
α = 70.069 (8)°	0.35 × 0.2 × 0.2 mm
β = 77.604 (9)°

Data collection top

Oxford Diffraction SuperNova (single source at offset) Atlas diffractometer	2917 independent reflections
Absorption correction: multi-scan (CrysAlis PRO; Oxford Diffraction, 2009)	2610 reflections with I > 2σ(I)
T_min = 0.117, T_max = 0.319	R_int = 0.017
5245 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.043	0 restraints
wR(F²) = 0.113	All H-atom parameters refined
S = 1.05	Δρ_max = 0.37 e Å⁻³
2917 reflections	Δρ_min = −0.44 e Å⁻³
230 parameters

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2σ(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 (Å²) top

	x	y	z	U_iso*/U_eq
C1	0.2330 (3)	0.4690 (2)	0.74281 (19)	0.0407 (4)
O1	0.1250 (3)	0.58486 (19)	0.68930 (16)	0.0679 (5)
C2	0.2780 (3)	0.4324 (2)	0.87982 (17)	0.0347 (4)
C3	0.3816 (3)	0.2896 (2)	0.94118 (19)	0.0391 (4)
H3	0.422 (3)	0.219 (2)	0.889 (2)	0.043 (6)*
C4	0.4253 (3)	0.2515 (2)	1.06806 (19)	0.0419 (4)
Cl4	0.55643 (9)	0.07373 (6)	1.14246 (6)	0.05951 (19)
C5	0.3676 (3)	0.3534 (2)	1.1378 (2)	0.0482 (5)
H5	0.393 (4)	0.325 (3)	1.228 (3)	0.074 (9)*
C6	0.2645 (3)	0.4939 (2)	1.0804 (2)	0.0454 (5)
H6	0.230 (4)	0.562 (3)	1.129 (3)	0.059 (7)*
C7	0.2178 (3)	0.5364 (2)	0.95170 (18)	0.0358 (4)
N8	0.1173 (3)	0.67993 (18)	0.88973 (17)	0.0415 (4)
H8	0.094 (4)	0.696 (3)	0.812 (3)	0.067 (8)*
C9	0.0393 (3)	0.7935 (2)	0.9426 (2)	0.0448 (5)
O10	0.0375 (3)	0.78715 (18)	1.05679 (17)	0.0650 (5)
C11	−0.0562 (4)	0.9388 (3)	0.8497 (3)	0.0545 (6)
H11B	−0.006 (4)	1.010 (3)	0.851 (3)	0.066 (8)*
H11A	−0.189 (5)	0.970 (4)	0.878 (3)	0.083 (10)*
Cl12	−0.03818 (13)	0.94573 (7)	0.68136 (7)	0.0826 (3)
C13	0.3127 (3)	0.3605 (2)	0.66429 (18)	0.0403 (4)
C14	0.5017 (3)	0.3148 (2)	0.61956 (19)	0.0465 (5)
Cl14	0.66554 (9)	0.37077 (10)	0.66357 (7)	0.0759 (2)
C15	0.5645 (5)	0.2289 (3)	0.5339 (2)	0.0701 (9)
H15	0.693 (6)	0.200 (4)	0.509 (4)	0.102 (12)*
C16	0.4381 (7)	0.1877 (3)	0.4935 (3)	0.0855 (12)
H16	0.478 (5)	0.129 (4)	0.433 (4)	0.109 (12)*
C17	0.2507 (8)	0.2312 (4)	0.5360 (3)	0.0885 (12)
H17	0.162 (6)	0.198 (4)	0.511 (4)	0.110 (13)*
C18	0.1858 (5)	0.3185 (3)	0.6211 (3)	0.0646 (7)
H18	0.054 (4)	0.345 (3)	0.647 (3)	0.064 (8)*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
C1	0.0457 (11)	0.0416 (10)	0.0345 (9)	−0.0059 (8)	−0.0076 (8)	−0.0154 (8)
O1	0.0874 (13)	0.0584 (10)	0.0450 (9)	0.0187 (9)	−0.0284 (8)	−0.0254 (8)
C2	0.0395 (9)	0.0372 (9)	0.0292 (8)	−0.0102 (8)	−0.0037 (7)	−0.0129 (7)
C3	0.0472 (11)	0.0362 (9)	0.0353 (9)	−0.0107 (8)	−0.0050 (8)	−0.0129 (8)
C4	0.0495 (11)	0.0382 (10)	0.0356 (9)	−0.0121 (8)	−0.0076 (8)	−0.0065 (8)
Cl4	0.0745 (4)	0.0419 (3)	0.0526 (3)	−0.0059 (3)	−0.0225 (3)	−0.0034 (2)
C5	0.0644 (14)	0.0501 (12)	0.0308 (9)	−0.0150 (10)	−0.0110 (9)	−0.0105 (9)
C6	0.0595 (13)	0.0464 (11)	0.0339 (10)	−0.0124 (9)	−0.0062 (9)	−0.0185 (9)
C7	0.0415 (10)	0.0362 (9)	0.0319 (9)	−0.0112 (8)	−0.0031 (7)	−0.0132 (7)
N8	0.0518 (10)	0.0364 (8)	0.0364 (9)	−0.0057 (7)	−0.0076 (7)	−0.0161 (7)
C9	0.0521 (12)	0.0401 (10)	0.0465 (11)	−0.0124 (9)	−0.0024 (9)	−0.0205 (9)
O10	0.0977 (14)	0.0495 (9)	0.0508 (9)	−0.0098 (9)	−0.0101 (9)	−0.0283 (8)
C11	0.0611 (15)	0.0390 (11)	0.0633 (14)	−0.0044 (10)	−0.0096 (12)	−0.0231 (10)
Cl12	0.1198 (6)	0.0491 (3)	0.0563 (4)	0.0106 (4)	−0.0247 (4)	−0.0128 (3)
C13	0.0556 (12)	0.0394 (10)	0.0296 (9)	−0.0123 (9)	−0.0095 (8)	−0.0129 (7)
C14	0.0579 (12)	0.0412 (10)	0.0317 (9)	0.0000 (9)	−0.0095 (9)	−0.0111 (8)
Cl14	0.0489 (3)	0.1181 (6)	0.0624 (4)	−0.0212 (4)	−0.0057 (3)	−0.0312 (4)
C15	0.101 (2)	0.0478 (13)	0.0343 (11)	0.0192 (14)	−0.0117 (13)	−0.0156 (10)
C16	0.172 (4)	0.0390 (12)	0.0384 (13)	−0.0081 (17)	−0.0247 (18)	−0.0161 (10)
C17	0.171 (4)	0.074 (2)	0.0541 (16)	−0.064 (2)	−0.033 (2)	−0.0190 (15)
C18	0.0825 (19)	0.0759 (17)	0.0535 (14)	−0.0381 (15)	−0.0126 (13)	−0.0231 (13)

Geometric parameters (Å, º) top

C1—O1	1.217 (3)	C9—O10	1.209 (3)
C1—C2	1.482 (2)	C9—C11	1.514 (3)
C1—C13	1.506 (3)	C11—Cl12	1.770 (3)
C2—C3	1.401 (3)	C11—H11B	0.93 (3)
C2—C7	1.417 (2)	C11—H11A	0.96 (3)
C3—C4	1.371 (3)	C13—C14	1.381 (3)
C3—H3	0.99 (2)	C13—C18	1.388 (3)
C4—C5	1.383 (3)	C14—C15	1.387 (3)
C4—Cl4	1.744 (2)	C14—Cl14	1.732 (2)
C5—C6	1.374 (3)	C15—C16	1.363 (5)
C5—H5	0.96 (3)	C15—H15	0.92 (4)
C6—C7	1.392 (3)	C16—C17	1.363 (6)
C6—H6	0.94 (3)	C16—H16	0.97 (4)
C7—N8	1.401 (3)	C17—C18	1.392 (4)
N8—C9	1.361 (3)	C17—H17	0.96 (4)
N8—H8	0.84 (3)	C18—H18	0.95 (3)

O1—C1—C2	122.49 (17)	N8—C9—C11	116.46 (19)
O1—C1—C13	116.25 (17)	C9—C11—Cl12	116.35 (15)
C2—C1—C13	121.21 (17)	C9—C11—H11B	109.2 (18)
C3—C2—C7	118.78 (17)	Cl12—C11—H11B	106.8 (18)
C3—C2—C1	118.91 (16)	C9—C11—H11A	111 (2)
C7—C2—C1	122.30 (17)	Cl12—C11—H11A	106 (2)
C4—C3—C2	120.57 (18)	H11B—C11—H11A	107 (3)
C4—C3—H3	122.2 (13)	C14—C13—C18	118.3 (2)
C2—C3—H3	117.3 (13)	C14—C13—C1	123.67 (19)
C3—C4—C5	120.60 (19)	C18—C13—C1	117.5 (2)
C3—C4—Cl4	120.01 (16)	C13—C14—C15	121.3 (3)
C5—C4—Cl4	119.38 (16)	C13—C14—Cl14	120.50 (15)
C6—C5—C4	120.02 (19)	C15—C14—Cl14	118.2 (2)
C6—C5—H5	119.4 (18)	C16—C15—C14	119.6 (3)
C4—C5—H5	120.5 (18)	C16—C15—H15	123 (2)
C5—C6—C7	120.93 (19)	C14—C15—H15	117 (2)
C5—C6—H6	118.3 (16)	C15—C16—C17	120.4 (2)
C7—C6—H6	120.8 (16)	C15—C16—H16	121 (2)
C6—C7—N8	121.99 (17)	C17—C16—H16	118 (2)
C6—C7—C2	119.09 (18)	C16—C17—C18	120.6 (3)
N8—C7—C2	118.90 (16)	C16—C17—H17	121 (2)
C9—N8—C7	128.23 (18)	C18—C17—H17	119 (3)
C9—N8—H8	116 (2)	C13—C18—C17	119.9 (3)
C7—N8—H8	116 (2)	C13—C18—H18	123.9 (17)
O10—C9—N8	125.6 (2)	C17—C18—H18	116.2 (17)
O10—C9—C11	117.95 (19)

O1—C1—C2—C3	170.9 (2)	C7—N8—C9—O10	−3.3 (4)
C13—C1—C2—C3	−6.2 (3)	C7—N8—C9—C11	178.0 (2)
O1—C1—C2—C7	−8.3 (3)	O10—C9—C11—Cl12	176.4 (2)
C13—C1—C2—C7	174.60 (18)	N8—C9—C11—Cl12	−4.8 (3)
C7—C2—C3—C4	−0.6 (3)	O1—C1—C13—C14	114.9 (2)
C1—C2—C3—C4	−179.76 (19)	C2—C1—C13—C14	−67.8 (3)
C2—C3—C4—C5	0.1 (3)	O1—C1—C13—C18	−56.9 (3)
C2—C3—C4—Cl4	−179.37 (15)	C2—C1—C13—C18	120.4 (2)
C3—C4—C5—C6	0.4 (4)	C18—C13—C14—C15	−0.2 (3)
Cl4—C4—C5—C6	179.89 (18)	C1—C13—C14—C15	−171.9 (2)
C4—C5—C6—C7	−0.5 (4)	C18—C13—C14—Cl14	176.90 (18)
C5—C6—C7—N8	−178.2 (2)	C1—C13—C14—Cl14	5.2 (3)
C5—C6—C7—C2	0.1 (3)	C13—C14—C15—C16	−0.4 (3)
C3—C2—C7—C6	0.4 (3)	Cl14—C14—C15—C16	−177.56 (19)
C1—C2—C7—C6	179.63 (19)	C14—C15—C16—C17	0.5 (4)
C3—C2—C7—N8	178.80 (18)	C15—C16—C17—C18	0.1 (5)
C1—C2—C7—N8	−2.0 (3)	C14—C13—C18—C17	0.7 (4)
C6—C7—N8—C9	−5.3 (3)	C1—C13—C18—C17	172.9 (2)
C2—C7—N8—C9	176.4 (2)	C16—C17—C18—C13	−0.7 (4)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N8—H8···O1	0.84 (3)	1.95 (3)	2.634 (2)	138 (3)
C6—H6···Cl14ⁱ	0.94 (3)	2.87 (3)	3.675 (2)	143 (2)
C11—H11B···O10ⁱⁱ	0.93 (3)	2.50 (3)	3.320 (3)	147 (2)
C18—H18···Cl14ⁱⁱⁱ	0.95 (3)	2.84 (3)	3.745 (3)	161 (2)

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

Experimental details

Crystal data
Chemical formula	C₁₅H₁₀Cl₃NO₂
M_r	342.59
Crystal system, space group	Triclinic, P1
Temperature (K)	295
a, b, c (Å)	7.5776 (9), 10.1565 (10), 10.7862 (12)
α, β, γ (°)	70.069 (8), 77.604 (9), 70.388 (8)
V (Å³)	730.47 (14)
Z	2
Radiation type	Cu Kα
µ (mm⁻¹)	5.71
Crystal size (mm)	0.35 × 0.2 × 0.2

Data collection
Diffractometer	Oxford Diffraction SuperNova (single source at offset) Atlas
Absorption correction	Multi-scan (CrysAlis PRO; Oxford Diffraction, 2009)
T_min, T_max	0.117, 0.319
No. of measured, independent and observed [I > 2σ(I)] reflections	5245, 2917, 2610
R_int	0.017
(sin θ/λ)_max (Å⁻¹)	0.627

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.043, 0.113, 1.05
No. of reflections	2917
No. of parameters	230
H-atom treatment	All H-atom parameters refined
Δρ_max, Δρ_min (e Å⁻³)	0.37, −0.44

Computer programs: CrysAlis PRO (Oxford Diffraction, 2009), SIR92 (Altomare et al., 1993), SHELXL97 (Sheldrick, 2008), Stereochemical Workstation Operation Manual (Siemens, 1989).