4-Methyl­anilinium tri­chloro­acetate

Suresh, S.; Pandi, P.; Kumar, R.M.; Chakkaravarthi, G.

doi:10.1107/S2414314617017679

organic compounds

IUCrDATA

ISSN: 2414-3146

Volume 2| Part 12| December 2017| x171767

https://doi.org/10.1107/S2414314617017679

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4-Methylanilinium trichloroacetate

S. Suresh,^a P. Pandi,^b R. Mohan Kumar ^a ^* and G. Chakkaravarthi ^c ^*

^aDepartment of Physics, Presidency College, Chennai 600 005, India, ^bDepartment of Physics, Panimalar Engineering College, Chennai 600 123, India, and ^cDepartment of Physics, CPCL Polytechnic College, Chennai 600 068, India
^*Correspondence e-mail: mohan66@hotmail.com, chakkaravarthi_2005@yahoo.com

Edited by W. T. A. Harrison, University of Aberdeen, Scotland (Received 9 December 2017; accepted 11 December 2017; online 15 December 2017)

The asymmetric unit of the title molecular salt, C₇H₁₀N⁺·C₂Cl₃O₂⁻, consists of two cations and two anions. In the crystal, N—H⋯O hydrogen bonds link the components into [100] chains incorporating R₂³(10) loops and weak π–π stacking [centroid-to-centroid distance = 3.865 (2) Å] is also observed.

Keywords: molecular salt; crystal structure; hydrogen bonding.

CCDC reference: 1590296

Structure description

We herewith report the synthesis and the crystal structure of the title molecular salt. Its geometric parameters agree well with those for reported similar structures (Babu et al., 2014 ; Benali-Cherif et al., 2009 ; Kalaiyarasi et al., 2017 ).

The asymmetric unit of the title compound (Fig. 1) comprises a pair of 4-methylanilinium cations and trichloroacetate anions. The dihedral angle between the benzene rings of the cations is 6.32 (1)°. Within the chosen asymmetric unit, N1—H1A⋯O4, N1—H1C⋯O2, N2—H2B⋯O3 and N2—H2C⋯O2 hydrogen bonds link the components, thereby generating an $[R_{2}^{3}]$ (10) loop and when symmetry-generated N2—H2A⋯O4ⁱⁱ, N1—H1B⋯O1ⁱ and N2—H2C⋯O2 hydrogen bonds are considered, another $[R_{2}^{3}]$ (10) loop is generated (Fig. 2, Table 1). The overall result is a supramolecular chain propagating along the a-axis direction (Fig. 3). The packing is further consolidated by weak π–π interactions [Cg1⋯Cg2 = 3.865 (2) Å; Cg1 and Cg2 are the centroids of the C1–C6 and C8–C13 rings, respectively].

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1A⋯O4	0.89	1.92	2.801 (3)	169
N1—H1B⋯O1ⁱ	0.89	1.91	2.796 (3)	172
N1—H1C⋯O2	0.89	1.96	2.834 (3)	167
N2—H2A⋯O4ⁱⁱ	0.89	1.98	2.851 (3)	165
N2—H2B⋯O3	0.89	1.86	2.745 (3)	172
N2—H2C⋯O2	0.89	1.92	2.789 (3)	164
Symmetry codes: (i) x-1, y, z; (ii) x+1, y, z.

Figure 1
The molecular structure with 30% probability displacement ellipsoids.

Figure 2
The crystal packing viewed down [010]. Hydrogen bonds are shown as dashed lines. H atoms not involving in hydrogen bonding have been omitted for clarity.

Figure 3
A partial view of the crystal packing, showing part of a [100] chain.

Synthesis and crystallization

p-Toluidine (1.33 g) and trichloroacetic acid (1.48 g) were taken in a 1:1 ratio and dissolved in water at room temperature and the solution was stirred for 6 h. It was filtered and kept for slow evaporation and colourless blocks were obtained after four weeks.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2.

Table 2
Experimental details

Crystal data
Chemical formula	C₇H₁₀N⁺·C₂Cl₃O₂⁻
M_r	270.53
Crystal system, space group	Triclinic, P $[\overline{1}]$
Temperature (K)	295
a, b, c (Å)	6.7395 (2), 11.3491 (3), 16.1078 (5)
α, β, γ (°)	75.681 (2), 88.031 (2), 86.856 (2)
V (Å³)	1191.69 (6)
Z	4
Radiation type	Cu Kα
μ (mm⁻¹)	6.82
Crystal size (mm)	0.26 × 0.22 × 0.18

Data collection
Diffractometer	Bruker APEXII CCD
Absorption correction	Multi-scan (SADABS; Bruker, 2004 )
T_min, T_max	0.386, 0.754
No. of measured, independent and observed [I > 2σ(I)] reflections	37675, 4685, 3713
R_int	0.066
(sin θ/λ)_max (Å⁻¹)	0.619

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.051, 0.128, 1.02
No. of reflections	4685
No. of parameters	275
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.45, −0.48
Computer programs: APEX2 (Bruker, 2004), SAINT (Bruker, 2004), SHELXT2016/6 (Sheldrick, 2015a ), SHELXL2016/6 (Sheldrick, 2015b ) and PLATON (Spek, 2009 ).

Structural data

CCDC reference: 1590296

Crystal structure: contains datablocks I, global. DOI: https://doi.org/10.1107/S2414314617017679/hb4190sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2414314617017679/hb4190Isup2.hkl

checkCIF report

Computing details top

Data collection: APEX2 (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT (Bruker, 2004); program(s) used to solve structure: SHELXT2016/6 (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2016/6 (Sheldrick, 2015b); molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: SHELXL2016/6 (Sheldrick, 2015b) and PLATON (Spek, 2009).

bis-(4-Methylanilinium trichloroacetate) top

Crystal data top

C₇H₁₀N⁺·C₂Cl₃O₂⁻	Z = 4
M_r = 270.53	F(000) = 552
Triclinic, P1	D_x = 1.508 Mg m⁻³
a = 6.7395 (2) Å	Cu Kα radiation, λ = 1.54178 Å
b = 11.3491 (3) Å	Cell parameters from 9965 reflections
c = 16.1078 (5) Å	θ = 2.8–70.5°
α = 75.681 (2)°	µ = 6.82 mm⁻¹
β = 88.031 (2)°	T = 295 K
γ = 86.856 (2)°	Block, colourless
V = 1191.69 (6) Å³	0.26 × 0.22 × 0.18 mm

Data collection top

Bruker APEXII CCD diffractometer	3713 reflections with I > 2σ(I)
ω and φ scans	R_int = 0.066
Absorption correction: multi-scan (SADABS; Bruker, 2004)	θ_max = 72.5°, θ_min = 2.8°
T_min = 0.386, T_max = 0.754	h = −8→8
37675 measured reflections	k = −14→13
4685 independent reflections	l = −19→19

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.051	H-atom parameters constrained
wR(F²) = 0.128	w = 1/[σ²(F_o²) + (0.0459P)² + 1.3481P] where P = (F_o² + 2F_c²)/3
S = 1.02	(Δ/σ)_max < 0.001
4685 reflections	Δρ_max = 0.45 e Å⁻³
275 parameters	Δρ_min = −0.48 e Å⁻³
0 restraints

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.

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

	x	y	z	U_iso*/U_eq
C1	0.0236 (4)	0.8176 (3)	0.3452 (2)	0.0550 (8)
C2	0.0345 (5)	0.7010 (4)	0.3974 (2)	0.0626 (9)
H2	0.032750	0.690668	0.456533	0.075*
C3	0.0480 (5)	0.5996 (3)	0.36460 (19)	0.0560 (8)
H3	0.054310	0.521988	0.401045	0.067*
C4	0.0519 (4)	0.6150 (3)	0.27675 (17)	0.0412 (6)
C5	0.0444 (4)	0.7297 (3)	0.22276 (18)	0.0464 (7)
H5	0.049155	0.739887	0.163650	0.056*
C6	0.0297 (4)	0.8296 (3)	0.2575 (2)	0.0538 (8)
H6	0.023774	0.907162	0.220901	0.065*
C7	0.0015 (7)	0.9265 (4)	0.3818 (3)	0.0829 (12)
H7A	−0.045476	0.995783	0.338455	0.124*
H7B	0.127876	0.942503	0.401343	0.124*
H7C	−0.092142	0.911241	0.429039	0.124*
C8	0.5084 (5)	0.9077 (3)	0.2121 (2)	0.0620 (9)
C9	0.5367 (4)	0.7938 (3)	0.2677 (2)	0.0579 (9)
H9	0.542346	0.787788	0.326206	0.069*
C10	0.5568 (4)	0.6891 (3)	0.2385 (2)	0.0506 (7)
H10	0.577655	0.613701	0.276898	0.061*
C11	0.5456 (4)	0.6972 (3)	0.15239 (19)	0.0482 (7)
C12	0.5148 (6)	0.8089 (3)	0.0954 (2)	0.0672 (10)
H12	0.506275	0.814448	0.037024	0.081*
C13	0.4969 (6)	0.9119 (4)	0.1260 (3)	0.0755 (11)
H13	0.476311	0.987076	0.087357	0.091*
C14	0.4872 (7)	1.0201 (4)	0.2444 (3)	0.0934 (14)
H14A	0.584074	1.076280	0.216207	0.140*
H14B	0.507760	0.999367	0.305112	0.140*
H14C	0.356226	1.056932	0.232833	0.140*
C15	0.4706 (4)	0.2780 (3)	0.40294 (18)	0.0430 (6)
C16	0.5665 (4)	0.3595 (3)	0.32056 (17)	0.0395 (6)
C17	−0.0049 (4)	0.7259 (3)	−0.07151 (18)	0.0441 (6)
C18	0.0910 (4)	0.6342 (3)	0.00763 (17)	0.0399 (6)
N1	0.0600 (3)	0.5075 (2)	0.24171 (15)	0.0443 (6)
H1A	0.048514	0.530754	0.185045	0.066*
H1B	−0.039197	0.460317	0.264266	0.066*
H1C	0.175484	0.466167	0.254491	0.066*
N2	0.5668 (3)	0.5879 (2)	0.12006 (16)	0.0503 (6)
H2A	0.686813	0.583562	0.095871	0.076*
H2B	0.474359	0.590779	0.081347	0.076*
H2C	0.552053	0.522479	0.163241	0.076*
O1	0.7457 (3)	0.3714 (3)	0.32515 (15)	0.0670 (7)
O2	0.4537 (3)	0.40509 (19)	0.26125 (12)	0.0499 (5)
O3	0.2719 (3)	0.6182 (2)	0.00216 (16)	0.0661 (7)
O4	−0.0249 (3)	0.59187 (19)	0.06740 (12)	0.0466 (5)
Cl1	0.45338 (17)	0.36565 (11)	0.47998 (6)	0.0839 (3)
Cl2	0.6160 (2)	0.14573 (9)	0.44281 (9)	0.1000 (4)
Cl3	0.22772 (14)	0.23875 (9)	0.38605 (6)	0.0722 (3)
Cl4	−0.25288 (12)	0.69394 (8)	−0.08705 (5)	0.0618 (2)
Cl5	0.12882 (16)	0.72723 (10)	−0.16713 (5)	0.0763 (3)
Cl6	−0.00309 (17)	0.87155 (8)	−0.04977 (7)	0.0793 (3)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
C1	0.0387 (15)	0.067 (2)	0.060 (2)	−0.0023 (14)	0.0021 (14)	−0.0174 (17)
C2	0.065 (2)	0.079 (2)	0.0420 (17)	0.0003 (18)	0.0085 (15)	−0.0140 (17)
C3	0.0583 (19)	0.064 (2)	0.0375 (15)	0.0028 (16)	0.0036 (14)	0.0015 (14)
C4	0.0248 (12)	0.0574 (17)	0.0375 (14)	−0.0010 (11)	0.0005 (10)	−0.0046 (12)
C5	0.0349 (14)	0.0619 (19)	0.0368 (14)	−0.0077 (13)	−0.0016 (11)	−0.0001 (13)
C6	0.0408 (16)	0.0560 (19)	0.0592 (19)	−0.0052 (14)	−0.0050 (14)	−0.0028 (15)
C7	0.087 (3)	0.080 (3)	0.086 (3)	0.001 (2)	−0.002 (2)	−0.031 (2)
C8	0.0458 (18)	0.060 (2)	0.073 (2)	−0.0049 (15)	0.0028 (16)	−0.0038 (18)
C9	0.0386 (16)	0.075 (2)	0.0522 (18)	−0.0080 (15)	−0.0074 (13)	0.0011 (17)
C10	0.0324 (14)	0.0570 (19)	0.0515 (17)	−0.0041 (13)	−0.0056 (12)	0.0085 (14)
C11	0.0260 (13)	0.0595 (19)	0.0473 (16)	−0.0008 (12)	0.0054 (11)	0.0083 (14)
C12	0.074 (2)	0.064 (2)	0.0483 (19)	0.0094 (18)	0.0103 (17)	0.0124 (16)
C13	0.083 (3)	0.061 (2)	0.063 (2)	0.0072 (19)	0.0108 (19)	0.0175 (18)
C14	0.094 (3)	0.076 (3)	0.107 (4)	−0.003 (2)	−0.002 (3)	−0.017 (3)
C15	0.0493 (16)	0.0399 (15)	0.0378 (14)	−0.0077 (12)	0.0016 (12)	−0.0048 (12)
C16	0.0388 (14)	0.0420 (15)	0.0363 (14)	−0.0039 (11)	0.0059 (11)	−0.0072 (12)
C17	0.0481 (16)	0.0450 (16)	0.0368 (14)	−0.0029 (13)	0.0008 (12)	−0.0053 (12)
C18	0.0392 (14)	0.0414 (15)	0.0382 (14)	−0.0044 (11)	−0.0047 (11)	−0.0070 (12)
N1	0.0317 (11)	0.0589 (15)	0.0370 (12)	−0.0013 (10)	0.0004 (9)	−0.0024 (11)
N2	0.0333 (12)	0.0605 (16)	0.0456 (14)	0.0021 (11)	0.0035 (10)	0.0076 (12)
O1	0.0368 (11)	0.0967 (19)	0.0588 (14)	−0.0150 (12)	0.0041 (10)	−0.0004 (13)
O2	0.0431 (11)	0.0593 (13)	0.0380 (10)	−0.0017 (9)	0.0012 (9)	0.0056 (9)
O3	0.0335 (11)	0.0805 (17)	0.0731 (15)	−0.0048 (11)	−0.0063 (10)	0.0039 (13)
O4	0.0440 (11)	0.0584 (12)	0.0314 (10)	0.0035 (9)	0.0008 (8)	−0.0014 (9)
Cl1	0.0997 (8)	0.1091 (8)	0.0561 (5)	−0.0204 (6)	0.0153 (5)	−0.0441 (5)
Cl2	0.1093 (9)	0.0528 (5)	0.1176 (9)	0.0153 (5)	−0.0250 (7)	0.0163 (6)
Cl3	0.0624 (5)	0.0783 (6)	0.0699 (6)	−0.0369 (4)	0.0035 (4)	−0.0006 (4)
Cl4	0.0522 (4)	0.0709 (5)	0.0558 (5)	0.0019 (4)	−0.0188 (4)	−0.0020 (4)
Cl5	0.0892 (7)	0.0884 (7)	0.0452 (4)	−0.0131 (5)	0.0221 (4)	−0.0065 (4)
Cl6	0.1087 (8)	0.0431 (4)	0.0869 (7)	0.0003 (5)	−0.0135 (6)	−0.0166 (4)

Geometric parameters (Å, º) top

C1—C2	1.381 (5)	C12—C13	1.375 (6)
C1—C6	1.385 (5)	C12—H12	0.9300
C1—C7	1.494 (5)	C13—H13	0.9300
C2—C3	1.378 (5)	C14—H14A	0.9600
C2—H2	0.9300	C14—H14B	0.9600
C3—C4	1.382 (4)	C14—H14C	0.9600
C3—H3	0.9300	C15—C16	1.560 (4)
C4—C5	1.375 (4)	C15—Cl2	1.741 (3)
C4—N1	1.463 (4)	C15—Cl3	1.767 (3)
C5—C6	1.380 (5)	C15—Cl1	1.770 (3)
C5—H5	0.9300	C16—O1	1.230 (3)
C6—H6	0.9300	C16—O2	1.233 (3)
C7—H7A	0.9600	C17—C18	1.566 (4)
C7—H7B	0.9600	C17—Cl5	1.755 (3)
C7—H7C	0.9600	C17—Cl4	1.769 (3)
C8—C13	1.380 (6)	C17—Cl6	1.773 (3)
C8—C9	1.386 (5)	C18—O3	1.226 (3)
C8—C14	1.491 (6)	C18—O4	1.236 (3)
C9—C10	1.381 (5)	N1—H1A	0.8900
C9—H9	0.9300	N1—H1B	0.8900
C10—C11	1.372 (4)	N1—H1C	0.8900
C10—H10	0.9300	N2—H2A	0.8900
C11—C12	1.379 (4)	N2—H2B	0.8900
C11—N2	1.458 (4)	N2—H2C	0.8900

C2—C1—C6	117.4 (3)	C12—C13—C8	122.3 (3)
C2—C1—C7	121.3 (3)	C12—C13—H13	118.8
C6—C1—C7	121.3 (3)	C8—C13—H13	118.8
C3—C2—C1	122.0 (3)	C8—C14—H14A	109.5
C3—C2—H2	119.0	C8—C14—H14B	109.5
C1—C2—H2	119.0	H14A—C14—H14B	109.5
C2—C3—C4	119.0 (3)	C8—C14—H14C	109.5
C2—C3—H3	120.5	H14A—C14—H14C	109.5
C4—C3—H3	120.5	H14B—C14—H14C	109.5
C5—C4—C3	120.6 (3)	C16—C15—Cl2	111.6 (2)
C5—C4—N1	120.2 (3)	C16—C15—Cl3	112.51 (19)
C3—C4—N1	119.2 (3)	Cl2—C15—Cl3	109.27 (16)
C4—C5—C6	119.1 (3)	C16—C15—Cl1	106.45 (19)
C4—C5—H5	120.4	Cl2—C15—Cl1	109.14 (16)
C6—C5—H5	120.4	Cl3—C15—Cl1	107.67 (16)
C5—C6—C1	121.9 (3)	O1—C16—O2	129.0 (3)
C5—C6—H6	119.1	O1—C16—C15	114.4 (2)
C1—C6—H6	119.1	O2—C16—C15	116.5 (2)
C1—C7—H7A	109.5	C18—C17—Cl5	112.3 (2)
C1—C7—H7B	109.5	C18—C17—Cl4	112.67 (19)
H7A—C7—H7B	109.5	Cl5—C17—Cl4	107.38 (16)
C1—C7—H7C	109.5	C18—C17—Cl6	106.09 (19)
H7A—C7—H7C	109.5	Cl5—C17—Cl6	109.53 (16)
H7B—C7—H7C	109.5	Cl4—C17—Cl6	108.85 (16)
C13—C8—C9	117.1 (4)	O3—C18—O4	129.5 (3)
C13—C8—C14	121.7 (4)	O3—C18—C17	114.8 (2)
C9—C8—C14	121.2 (4)	O4—C18—C17	115.6 (2)
C10—C9—C8	121.8 (3)	C4—N1—H1A	109.5
C10—C9—H9	119.1	C4—N1—H1B	109.5
C8—C9—H9	119.1	H1A—N1—H1B	109.5
C11—C10—C9	119.4 (3)	C4—N1—H1C	109.5
C11—C10—H10	120.3	H1A—N1—H1C	109.5
C9—C10—H10	120.3	H1B—N1—H1C	109.5
C10—C11—C12	120.4 (3)	C11—N2—H2A	109.5
C10—C11—N2	120.4 (3)	C11—N2—H2B	109.5
C12—C11—N2	119.2 (3)	H2A—N2—H2B	109.5
C13—C12—C11	119.1 (4)	C11—N2—H2C	109.5
C13—C12—H12	120.5	H2A—N2—H2C	109.5
C11—C12—H12	120.5	H2B—N2—H2C	109.5

C6—C1—C2—C3	−1.0 (5)	N2—C11—C12—C13	−179.4 (3)
C7—C1—C2—C3	177.7 (3)	C11—C12—C13—C8	−0.1 (6)
C1—C2—C3—C4	0.4 (5)	C9—C8—C13—C12	−0.8 (6)
C2—C3—C4—C5	0.6 (5)	C14—C8—C13—C12	−179.6 (4)
C2—C3—C4—N1	−178.1 (3)	Cl2—C15—C16—O1	−44.8 (3)
C3—C4—C5—C6	−1.0 (4)	Cl3—C15—C16—O1	−168.1 (2)
N1—C4—C5—C6	177.7 (2)	Cl1—C15—C16—O1	74.2 (3)
C4—C5—C6—C1	0.4 (4)	Cl2—C15—C16—O2	136.9 (2)
C2—C1—C6—C5	0.6 (5)	Cl3—C15—C16—O2	13.6 (3)
C7—C1—C6—C5	−178.1 (3)	Cl1—C15—C16—O2	−104.1 (3)
C13—C8—C9—C10	1.3 (5)	Cl5—C17—C18—O3	29.9 (3)
C14—C8—C9—C10	−179.9 (3)	Cl4—C17—C18—O3	151.3 (2)
C8—C9—C10—C11	−1.0 (4)	Cl6—C17—C18—O3	−89.7 (3)
C9—C10—C11—C12	0.0 (4)	Cl5—C17—C18—O4	−152.5 (2)
C9—C10—C11—N2	179.9 (2)	Cl4—C17—C18—O4	−31.1 (3)
C10—C11—C12—C13	0.5 (5)	Cl6—C17—C18—O4	87.9 (3)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···O4	0.89	1.92	2.801 (3)	169
N1—H1B···O1ⁱ	0.89	1.91	2.796 (3)	172
N1—H1C···O2	0.89	1.96	2.834 (3)	167
N2—H2A···O4ⁱⁱ	0.89	1.98	2.851 (3)	165
N2—H2B···O3	0.89	1.86	2.745 (3)	172
N2—H2C···O2	0.89	1.92	2.789 (3)	164

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

Acknowledgements

The authors acknowledge the SAIF, IIT, Madras for the data collection.

References

Babu, K. S. S., Peramaiyan, G., NizamMohideen, M. & Mohan, R. (2014). Acta Cryst. E70, o391–o392. CSD CrossRef CAS IUCr Journals Google Scholar
Benali-Cherif, N., Boussekine, H., Boutobba, Z. & Dadda, N. (2009). Acta Cryst. E65, o2744. Web of Science CSD CrossRef IUCr Journals Google Scholar
Bruker (2004). APEX2, SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Kalaiyarasi, S., Suresh, S., Akilan, R., Kumar, R. M. & Chakkaravarthi, G. (2017). IUCrData, 2, x170254. Google Scholar
Sheldrick, G. M. (2015a). Acta Cryst. A71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar
Sheldrick, G. M. (2015b). Acta Cryst. C71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar
Spek, A. L. (2009). Acta Cryst. D65, 148–155. Web of Science CrossRef CAS IUCr Journals Google Scholar

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