2-Methyl-N-(4-methyl­phen­yl)benzamide

Gowda, B.T.; Tokarčík, M.; Kožíšek, J.; Sowmya, B.P.; Fuess, H.

doi:10.1107/S1600536808021235

organic compounds

CRYSTALLOGRAPHIC
COMMUNICATIONS

ISSN: 2056-9890

Volume 64| Part 8| August 2008| Page o1494

doi:10.1107/S1600536808021235

Open

access

2-Methyl-N-(4-methylphenyl)benzamide

B. Thimme Gowda,^a ^* Miroslav Tokarčík,^b Jozef Kožíšek,^b B. P. Sowmya ^a and Hartmut Fuess ^c

^aDepartment of Chemistry, Mangalore University, Mangalagangotri 574 199, Mangalore, India, ^bFaculty of Chemical and Food Technology, Slovak Technical University, Radlinského 9, SK-812 37 Bratislava, Slovak Republic, and ^cInstitute of Materials Science, Darmstadt University of Technology, Petersenstrasse 23, D-64287 Darmstadt, Germany
^*Correspondence e-mail: gowdabt@yahoo.com

(Received 7 July 2008; accepted 8 July 2008; online 16 July 2008)

The conformations of the N—H and C=O bonds in the structure of the title compound, C₁₅H₁₅NO, are trans to each other. Furthermore, the position of the amide O atom is syn to the ortho-methyl group in the benzoyl ring. The central amide group is tilted at an angle of 59.96 (11)° to the benzoyl ring, and the benzoyl and aniline rings form a dihedral angle of 81.44 (5)°. N—H⋯O hydrogen bonds link the molecules into infinite chains running along the c axis.

Related literature

For related literature, see Gowda et al. (2003 , 2008a ,b ,c ).

Experimental

Crystal data

C₁₅H₁₅NO
M_r = 225.28
Monoclinic, C 2/c
a = 40.6634 (12) Å
b = 7.1770 (2) Å
c = 8.9418 (2) Å
β = 96.173 (3)°
V = 2594.45 (12) Å³
Z = 8
Mo Kα radiation
μ = 0.07 mm⁻¹
T = 295 (2) K
0.33 × 0.13 × 0.10 mm

Data collection

Oxford Diffraction Xcalibur System diffractometer
Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2007 $[Oxford Diffraction (2007). CrysAlis CCD and CrysAlis RED. Oxford Diffraction Ltd, Abingdon, Oxfordshire, England.]$ ) T_min = 0.985, T_max = 0.994
25372 measured reflections
2486 independent reflections
1594 reflections with I > 2σ(I)
R_int = 0.049

Refinement

R[F² > 2σ(F²)] = 0.045
wR(F²) = 0.121
S = 1.02
2486 reflections
159 parameters
4 restraints
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.13 e Å⁻³
Δρ_min = −0.11 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1N⋯O1ⁱ	0.868 (13)	1.973 (13)	2.8361 (15)	172.9 (15)
Symmetry code: (i) $[x, -y+1, z-{\script{1\over 2}}]$ .

Data collection: CrysAlis CCD (Oxford Diffraction, 2007 $[Oxford Diffraction (2007). CrysAlis CCD and CrysAlis RED. Oxford Diffraction Ltd, Abingdon, Oxfordshire, England.]$ ); cell refinement: CrysAlis RED (Oxford Diffraction, 2007 $[Oxford Diffraction (2007). CrysAlis CCD and CrysAlis RED. Oxford Diffraction Ltd, Abingdon, Oxfordshire, England.]$ ); data reduction: CrysAlis RED; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997 ) and DIAMOND (Brandenburg, 2002 ); software used to prepare material for publication: SHELXL97, PLATON (Spek, 2003 ) and WinGX (Farrugia, 1999 ).

Supporting information

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536808021235/tk2283sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536808021235/tk2283Isup2.hkl

checkCIF report

Comment top

As part of a study of exploring the effect of substituents on the structures of benzanilides (Gowda et al., 2003; 2008a,b,c), inthe present work, the structure of 2-methyl-N-(4-methylphenyl)benzamide (I) has been determined. The N—H and C=O bonds in the amide group of (I) are trans to each other (Fig. 1), similar to what is observed in N-(4-methylphenyl)benzamide (N4MPBA) (Gowda et al., 2008c), 2-methyl-N-(phenyl)-benzamide (NP2MBA) (Gowda et al., 2008a), and 2-methyl-N-(3-methylphenyl)-benzamide (N3MP2MBA) (Gowda et al., 2008b). Further, the conformation of the amide oxygen in (I) is syn to the ortho-methyl group in the benzoyl ring, similar to what is observed in NP2MBA and N3MP2MBA (Gowda et al., 2008a, b).

The central amide group is tilted to the benzoyl ring at the angle of 59.96 (11)°. The two rings (benzoyl and aniline) make a dihedral angle of 81.44 (5)°. N—H···O hydrogen bonds link the molecules into infinite chains running along the c-axis of the crystal (Table 1 & Fig. 2).

Related literature top

For related literature, see Gowda et al. (2003, 2008a,b,c).

Experimental top

The title compound was prepared according to the method described by Gowda et al. (2003). Prism-like colourless single crystals were obtained by slow evaporation from an ethanol solution of (I) (0.5 g in about 40 ml of ethanol) at room temperature.

Computing details top

Data collection: CrysAlis CCD (Oxford Diffraction, 2007); cell refinement: CrysAlis RED (Oxford Diffraction, 2007); data reduction: CrysAlis RED (Oxford Diffraction, 2007); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997) and DIAMOND (Brandenburg, 2002); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008), PLATON (Spek, 2003) and WinGX (Farrugia, 1999).

Figures top

	Fig. 1. Molecular structure of (I) showing the atom labelling scheme and displacement ellipsoids at the 30% probability level.
	Fig. 2. Part of crystal structure of (I) viewed down the b-axis. Hydrogen bonds N1–H1N···O1(i) give rise to infinite molecular chains running along the c axis. Symmetry code: (i) x,-y + 1,z - 1/2. H atoms not involved in hydrogen bonding are omitted and hydrogen bonds are shown as dashed lines.

2-Methyl-N-(4-methylphenyl)benzamide top

Crystal data top

C₁₅H₁₅NO	F(000) = 960
M_r = 225.28	D_x = 1.153 Mg m⁻³
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 6446 reflections
a = 40.6634 (12) Å	θ = 3.0–29.2°
b = 7.1770 (2) Å	µ = 0.07 mm⁻¹
c = 8.9418 (2) Å	T = 295 K
β = 96.173 (3)°	Prism, colourless
V = 2594.45 (12) Å³	0.33 × 0.13 × 0.10 mm
Z = 8

Data collection top

Oxford Diffraction Xcalibur System diffractometer	2486 independent reflections
Graphite monochromator	1594 reflections with I > 2σ(I)
Detector resolution: 10.434 pixels mm^-1	R_int = 0.049
ω scans with κ offsets	θ_max = 25.9°, θ_min = 5.4°
Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2007)	h = −49→49
T_min = 0.985, T_max = 0.994	k = −8→8
25372 measured reflections	l = −10→10

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)] = 0.045	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.121	H atoms treated by a mixture of independent and constrained refinement
S = 1.02	w = 1/[σ²(F_o²) + (0.0661P)² + 0.0615P] where P = (F_o² + 2F_c²)/3
2486 reflections	(Δ/σ)_max = 0.001
159 parameters	Δρ_max = 0.13 e Å⁻³
4 restraints	Δρ_min = −0.11 e Å⁻³

Crystal data top

C₁₅H₁₅NO	V = 2594.45 (12) Å³
M_r = 225.28	Z = 8
Monoclinic, C2/c	Mo Kα radiation
a = 40.6634 (12) Å	µ = 0.07 mm⁻¹
b = 7.1770 (2) Å	T = 295 K
c = 8.9418 (2) Å	0.33 × 0.13 × 0.10 mm
β = 96.173 (3)°

Data collection top

Oxford Diffraction Xcalibur System diffractometer	2486 independent reflections
Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2007)	1594 reflections with I > 2σ(I)
T_min = 0.985, T_max = 0.994	R_int = 0.049
25372 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.045	4 restraints
wR(F²) = 0.121	H atoms treated by a mixture of independent and constrained refinement
S = 1.02	Δρ_max = 0.13 e Å⁻³
2486 reflections	Δρ_min = −0.11 e Å⁻³
159 parameters

Special details top

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 (Å²) top

	x	y	z	U_iso*/U_eq	Occ. (<1)
C1	0.38556 (4)	0.3947 (2)	0.51508 (15)	0.0490 (4)
C2	0.41020 (4)	0.29352 (18)	0.43275 (14)	0.0460 (4)
C3	0.44366 (4)	0.2966 (2)	0.48505 (16)	0.0556 (4)
C4	0.46488 (4)	0.1922 (2)	0.4075 (2)	0.0683 (5)
H4	0.4874	0.193	0.4397	0.082*
C5	0.45356 (5)	0.0877 (2)	0.2846 (2)	0.0744 (5)
H5	0.4683	0.0168	0.236	0.089*
C6	0.42084 (5)	0.0867 (2)	0.23294 (19)	0.0712 (5)
H6	0.4132	0.0166	0.1488	0.085*
C7	0.39921 (4)	0.1908 (2)	0.30672 (15)	0.0577 (4)
H7	0.3769	0.192	0.2712	0.069*
C8	0.34387 (4)	0.6436 (2)	0.48652 (14)	0.0508 (4)
C9	0.32161 (4)	0.5851 (2)	0.58239 (17)	0.0654 (5)
H9	0.3219	0.4626	0.6163	0.078*
C10	0.29882 (4)	0.7110 (3)	0.6277 (2)	0.0785 (5)
H10	0.2839	0.6706	0.6926	0.094*
C11	0.29747 (4)	0.8930 (3)	0.5804 (2)	0.0752 (5)
C12	0.32004 (5)	0.9467 (3)	0.4855 (2)	0.0799 (5)
H12	0.3199	1.0694	0.452	0.096*
C13	0.34283 (4)	0.8252 (3)	0.43868 (18)	0.0697 (5)
H13	0.3577	0.8664	0.3739	0.084*
C14	0.45688 (5)	0.4126 (3)	0.6189 (2)	0.0896 (6)
H14A	0.4806	0.4132	0.6273	0.134*
H14B	0.4496	0.3606	0.7087	0.134*
H14C	0.4488	0.538	0.606	0.134*
C15	0.27185 (5)	1.0262 (4)	0.6292 (3)	0.1144 (9)
H15A	0.2567	0.9594	0.6848	0.172*	0.5
H15B	0.2599	1.0821	0.542	0.172*	0.5
H15C	0.2826	1.1217	0.6917	0.172*	0.5
H15D	0.2761	1.1494	0.5942	0.172*	0.5
H15E	0.2729	1.0267	0.737	0.172*	0.5
H15F	0.2502	0.9871	0.5873	0.172*	0.5
N1	0.36770 (3)	0.52332 (18)	0.43453 (13)	0.0545 (4)
H1N	0.3735 (4)	0.552 (2)	0.3467 (15)	0.065*
O1	0.38239 (3)	0.35884 (16)	0.64635 (11)	0.0718 (4)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
C1	0.0637 (9)	0.0501 (9)	0.0351 (7)	−0.0025 (7)	0.0132 (6)	−0.0003 (6)
C2	0.0611 (9)	0.0411 (8)	0.0374 (7)	0.0016 (7)	0.0133 (6)	0.0030 (6)
C3	0.0646 (10)	0.0491 (9)	0.0537 (9)	0.0001 (8)	0.0091 (7)	−0.0005 (7)
C4	0.0587 (10)	0.0634 (11)	0.0843 (12)	0.0030 (9)	0.0147 (9)	0.0005 (9)
C5	0.0779 (13)	0.0625 (12)	0.0871 (12)	0.0077 (10)	0.0293 (10)	−0.0164 (10)
C6	0.0846 (13)	0.0660 (12)	0.0653 (10)	−0.0002 (10)	0.0184 (9)	−0.0243 (9)
C7	0.0645 (10)	0.0597 (10)	0.0500 (8)	−0.0019 (8)	0.0107 (7)	−0.0079 (7)
C8	0.0518 (9)	0.0636 (10)	0.0376 (7)	0.0047 (8)	0.0082 (6)	−0.0023 (7)
C9	0.0613 (10)	0.0722 (11)	0.0655 (9)	−0.0040 (8)	0.0205 (8)	−0.0039 (8)
C10	0.0576 (10)	0.1063 (15)	0.0759 (11)	−0.0022 (10)	0.0265 (8)	−0.0135 (10)
C11	0.0625 (11)	0.0948 (13)	0.0667 (11)	0.0212 (10)	−0.0003 (9)	−0.0204 (10)
C12	0.0887 (13)	0.0752 (13)	0.0761 (11)	0.0250 (11)	0.0104 (10)	0.0027 (10)
C13	0.0773 (12)	0.0708 (12)	0.0641 (10)	0.0136 (10)	0.0214 (8)	0.0106 (9)
C14	0.0823 (13)	0.0965 (15)	0.0864 (12)	−0.0020 (11)	−0.0075 (10)	−0.0278 (11)
C15	0.0884 (15)	0.146 (2)	0.1076 (15)	0.0512 (15)	0.0038 (12)	−0.0354 (15)
N1	0.0660 (8)	0.0652 (9)	0.0352 (6)	0.0115 (7)	0.0185 (6)	0.0062 (6)
O1	0.1041 (9)	0.0757 (8)	0.0394 (6)	0.0222 (7)	0.0253 (5)	0.0099 (5)

Geometric parameters (Å, º) top

C1—O1	1.2219 (15)	C9—H9	0.93
C1—N1	1.3362 (18)	C10—C11	1.372 (3)
C1—C2	1.4941 (19)	C10—H10	0.93
C2—C7	1.380 (2)	C11—C12	1.370 (3)
C2—C3	1.390 (2)	C11—C15	1.513 (3)
C3—C4	1.384 (2)	C12—C13	1.371 (2)
C3—C14	1.509 (2)	C12—H12	0.93
C4—C5	1.369 (2)	C13—H13	0.93
C4—H4	0.93	C14—H14A	0.96
C5—C6	1.361 (2)	C14—H14B	0.96
C5—H5	0.93	C14—H14C	0.96
C6—C7	1.375 (2)	C15—H15A	0.96
C6—H6	0.93	C15—H15B	0.96
C7—H7	0.93	C15—H15C	0.96
C8—C13	1.372 (2)	C15—H15D	0.96
C8—C9	1.377 (2)	C15—H15E	0.96
C8—N1	1.4132 (19)	C15—H15F	0.96
C9—C10	1.386 (2)	N1—H1N	0.868 (13)

O1—C1—N1	123.78 (13)	C13—C12—H12	119
O1—C1—C2	121.10 (13)	C12—C13—C8	120.57 (17)
N1—C1—C2	115.12 (11)	C12—C13—H13	119.7
C7—C2—C3	120.17 (13)	C8—C13—H13	119.7
C7—C2—C1	119.10 (13)	C3—C14—H14A	109.5
C3—C2—C1	120.69 (12)	C3—C14—H14B	109.5
C4—C3—C2	117.58 (14)	H14A—C14—H14B	109.5
C4—C3—C14	120.54 (15)	C3—C14—H14C	109.5
C2—C3—C14	121.86 (14)	H14A—C14—H14C	109.5
C5—C4—C3	121.66 (16)	H14B—C14—H14C	109.5
C5—C4—H4	119.2	C11—C15—H15A	109.5
C3—C4—H4	119.2	C11—C15—H15B	109.5
C6—C5—C4	120.51 (15)	H15A—C15—H15B	109.5
C6—C5—H5	119.7	C11—C15—H15C	109.5
C4—C5—H5	119.7	H15A—C15—H15C	109.5
C5—C6—C7	119.13 (15)	H15B—C15—H15C	109.5
C5—C6—H6	120.4	C11—C15—H15D	109.5
C7—C6—H6	120.4	H15A—C15—H15D	141.1
C6—C7—C2	120.93 (15)	H15B—C15—H15D	56.3
C6—C7—H7	119.5	H15C—C15—H15D	56.3
C2—C7—H7	119.5	C11—C15—H15E	109.5
C13—C8—C9	118.91 (15)	H15A—C15—H15E	56.3
C13—C8—N1	118.50 (14)	H15B—C15—H15E	141.1
C9—C8—N1	122.59 (15)	H15C—C15—H15E	56.3
C8—C9—C10	119.25 (17)	H15D—C15—H15E	109.5
C8—C9—H9	120.4	C11—C15—H15F	109.5
C10—C9—H9	120.4	H15A—C15—H15F	56.3
C11—C10—C9	122.42 (17)	H15B—C15—H15F	56.3
C11—C10—H10	118.8	H15C—C15—H15F	141.1
C9—C10—H10	118.8	H15D—C15—H15F	109.5
C12—C11—C10	116.86 (16)	H15E—C15—H15F	109.5
C12—C11—C15	121.9 (2)	C1—N1—C8	126.63 (12)
C10—C11—C15	121.3 (2)	C1—N1—H1N	117.8 (11)
C11—C12—C13	122.00 (18)	C8—N1—H1N	114.6 (11)
C11—C12—H12	119

O1—C1—C2—C7	118.96 (16)	C13—C8—C9—C10	0.0 (2)
N1—C1—C2—C7	−60.69 (18)	N1—C8—C9—C10	−179.59 (14)
O1—C1—C2—C3	−58.66 (19)	C8—C9—C10—C11	0.1 (3)
N1—C1—C2—C3	121.68 (15)	C9—C10—C11—C12	−0.4 (3)
C7—C2—C3—C4	−0.8 (2)	C9—C10—C11—C15	178.70 (16)
C1—C2—C3—C4	176.82 (14)	C10—C11—C12—C13	0.4 (3)
C7—C2—C3—C14	177.70 (15)	C15—C11—C12—C13	−178.61 (17)
C1—C2—C3—C14	−4.7 (2)	C11—C12—C13—C8	−0.3 (3)
C2—C3—C4—C5	−0.7 (2)	C9—C8—C13—C12	0.0 (2)
C14—C3—C4—C5	−179.15 (16)	N1—C8—C13—C12	179.69 (14)
C3—C4—C5—C6	1.4 (3)	O1—C1—N1—C8	3.2 (2)
C4—C5—C6—C7	−0.6 (3)	C2—C1—N1—C8	−177.12 (14)
C5—C6—C7—C2	−0.8 (2)	C13—C8—N1—C1	139.57 (16)
C3—C2—C7—C6	1.5 (2)	C9—C8—N1—C1	−40.8 (2)
C1—C2—C7—C6	−176.10 (14)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1N···O1ⁱ	0.87 (1)	1.97 (1)	2.8361 (15)	173 (2)

Symmetry code: (i) x, −y+1, z−1/2.

Experimental details

Crystal data
Chemical formula	C₁₅H₁₅NO
M_r	225.28
Crystal system, space group	Monoclinic, C2/c
Temperature (K)	295
a, b, c (Å)	40.6634 (12), 7.1770 (2), 8.9418 (2)
β (°)	96.173 (3)
V (Å³)	2594.45 (12)
Z	8
Radiation type	Mo Kα
µ (mm⁻¹)	0.07
Crystal size (mm)	0.33 × 0.13 × 0.10

Data collection
Diffractometer	Oxford Diffraction Xcalibur System diffractometer
Absorption correction	Multi-scan (CrysAlis RED; Oxford Diffraction, 2007)
T_min, T_max	0.985, 0.994
No. of measured, independent and observed [I > 2σ(I)] reflections	25372, 2486, 1594
R_int	0.049
(sin θ/λ)_max (Å⁻¹)	0.615

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.045, 0.121, 1.02
No. of reflections	2486
No. of parameters	159
No. of restraints	4
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	0.13, −0.11

Computer programs: CrysAlis CCD (Oxford Diffraction, 2007), CrysAlis RED (Oxford Diffraction, 2007), SHELXS97 (Sheldrick, 2008), ORTEP-3 (Farrugia, 1997) and DIAMOND (Brandenburg, 2002), SHELXL97 (Sheldrick, 2008), PLATON (Spek, 2003) and WinGX (Farrugia, 1999).

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1N···O1ⁱ	0.868 (13)	1.973 (13)	2.8361 (15)	172.9 (15)

Symmetry code: (i) x, −y+1, z−1/2.

Acknowledgements

MT and JK thank the Grant Agency of the Slovak Republic (VEGA 1/0817/08) and Structural Funds (Interreg IIIA) for financial support in the purchase of the diffractometer.

References

Brandenburg, K. (2002). DIAMOND. Crystal Impact GbR, Bonn, Germany. Google Scholar
Farrugia, L. J. (1997). J. Appl. Cryst. 30, 565. CrossRef IUCr Journals Google Scholar
Farrugia, L. J. (1999). J. Appl. Cryst. 32, 837–838. CrossRef CAS IUCr Journals Google Scholar
Gowda, B. T., Foro, S., Sowmya, B. P. & Fuess, H. (2008a). Acta Cryst. E64, o383. Web of Science CSD CrossRef IUCr Journals Google Scholar
Gowda, B. T., Foro, S., Sowmya, B. P. & Fuess, H. (2008b). Acta Cryst. E64, o541. Web of Science CSD CrossRef IUCr Journals Google Scholar
Gowda, B. T., Jyothi, K., Paulus, H. & Fuess, H. (2003). Z. Naturforsch. Teil A, 58, 225–230. CAS Google Scholar
Gowda, B. T., Tokarčík, M., Kožíšek, J. & Sowmya, B. P. (2008c). Acta Cryst. E64, o83. Web of Science CSD CrossRef IUCr Journals Google Scholar
Oxford Diffraction (2007). CrysAlis CCD and CrysAlis RED. Oxford Diffraction Ltd, Abingdon, Oxfordshire, England. Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Spek, A. L. (2003). J. Appl. Cryst. 36, 7–13. Web of Science CrossRef CAS IUCr Journals Google Scholar