Charge-density analysis and electrostatic properties of 2-carboxy-4-methylanilinium chloride mono­hydrate obtained using a multipolar and a spherical-charges model

The new crystal structure of 2-carboxy-4-methylanilinium chloride monohydrate was determined by X-ray diffraction and refined using three different electron-density models. In the first model, the ELMAM2 multipolar electron-density database was transferred to the molecule. Theoretical structure factors were also computed from periodic density functional theory calculations and yielded, after multipolar-atoms refinement, the second charge-density model. An alternative electron-density modelling, based on spherical atoms and additional charges on the covalent bonds and electron lone-pair sites, was used in the third model in the refinement versus the theoretical data. The crystallographic refinements, structural properties, electron-density distributions and molecular electrostatic potentials obtained from the different charge-density models were compared. As the number of variables refined in the different models is the same, the R factor is a good indicator of refinement quality. The R factor is best for multipolar modelling, presumably because of the greater flexibility and larger number of parameters to model the electron density compared to the spherical-charges model. The electrostatic potentials around the molecule show a high correlation coefficient between the three models.

Computing details

Program(s) used to solve structure: SHELXL97 (Sheldrick, 1997); program(s) used to refine structure: MoPro (J. Appl. Cryst. 2005, 38, 38-54); molecular graphics: MoPro (J. Appl. Cryst. 2005, 38, 38-54); software used to prepare material for publication: MoPro (J. Appl. Cryst. 2005, 38, 38-54).

2-carboxy-4-methylanilinium chloride monohydride

Crystal data

C8H10NO2·H2O·Cl	F(000) = 432
Mr = 205.63	Dx = 1.410 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 2630 reflections
a = 10.051 (5) Å	θ = 4.1–28.1°
b = 4.9629 (17) Å	µ = 0.37 mm^−1
c = 19.563 (15) Å	T = 100 K
β = 96.77 (2)°	Prism, yellow
V = 969.0 (9) Å^3	0.20 × 0.15 × 0.11 mm
Z = 4

Data collection

Appex II CCD detector diffractometer	2276 independent reflections
Radiation source: fine-focus sealed tube	2083 reflections with > 2.0σ(I)
Graphite monochromator	θmax = 28.1°, θmin = 4.1°
w scan	h = 0→13
Absorption correction: multi-scan 'R. H. Blessing(1995) Acta. Cryst. A51,33-38.'	k = 0→6
Tmin = 0.930, Tmax = 0.971	l = −25→25
2368 measured reflections

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)] = 0.035	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.146	H-atom parameters constrained
S = 1.24	w = 1/[σ^2(Fo^2) + (0.1P)^2 + 0.01P] where P = (Fo^2 + 2Fc^2)/3
2276 reflections	(Δ/σ)max < 0.001
118 parameters	Δρmax = 0.43 e Å^−3
0 restraints	Δρmin = −0.29 e Å^−3

Special details

Refinement. Refinement of F² against reflections. The threshold expression of F² > σ(F²) is used for calculating R-factors(gt) 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
CL1	0.840005 (4)	0.50212 (7)	0.32288 (2)	0.0152 (1)
O2	0.3736 (1)	0.5245 (2)	0.36543 (8)	0.0208 (3)
O1	0.1742 (1)	0.4690 (2)	0.30180 (7)	0.0177 (3)
O3	0.5710 (1)	0.3271 (2)	0.23972 (6)	0.0193 (3)
N1	0.0343 (2)	0.0124 (2)	0.32497 (8)	0.0145 (4)
C1	0.2279 (2)	0.2010 (3)	0.40341 (8)	0.0141 (4)
C6	0.3078 (2)	0.1902 (3)	0.46724 (8)	0.0161 (4)
C3	0.0972 (2)	−0.1695 (3)	0.44081 (9)	0.0157 (4)
C4	0.1776 (2)	−0.1740 (3)	0.50391 (9)	0.0169 (4)
C7	0.3713 (2)	0.0019 (3)	0.5870 (1)	0.0213 (5)
C5	0.2845 (2)	0.0050 (3)	0.51811 (10)	0.0155 (5)
C2	0.1218 (2)	0.0166 (3)	0.39086 (9)	0.0135 (4)
C8	0.2539 (2)	0.4093 (3)	0.35127 (8)	0.0143 (4)
H3	0.02700	−0.29142	0.43216	0.01881*
H6	0.37877	0.31050	0.47587	0.01933*
H4	0.15975	−0.29857	0.53717	0.02024*
H1A	0.08439	0.01226	0.29036	0.02179*
H1C	−0.01802	0.15755	0.32198	0.02179*
H1B	−0.01628	−0.13526	0.32274	0.02179*
H2	0.38308	0.64041	0.33651	0.03121*
H7A	0.32283	0.08056	0.62145	0.03199*
H7B	0.39458	−0.18059	0.59948	0.03199*
H7C	0.45144	0.10386	0.58362	0.03199*
H1W	0.52536	0.46435	0.23820	0.02895*
H2W	0.64006	0.37879	0.26246	0.02895*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
CL1	0.0145 (3)	0.0148 (3)	0.0161 (3)	−0.0012 (1)	0.0012 (2)	−0.0006 (1)
O2	0.0172 (7)	0.0222 (7)	0.0222 (7)	−0.0058 (5)	−0.0007 (5)	0.0077 (5)
O1	0.0190 (7)	0.0173 (6)	0.0162 (7)	−0.0014 (4)	−0.0010 (5)	0.0022 (4)
O3	0.0154 (6)	0.0203 (6)	0.0212 (6)	0.0023 (5)	−0.0018 (5)	−0.0052 (5)
N1	0.0164 (8)	0.0146 (8)	0.0121 (7)	−0.0006 (5)	−0.0002 (6)	−0.0005 (5)
C1	0.0146 (7)	0.0136 (8)	0.0143 (8)	0.0014 (6)	0.0021 (6)	−0.0005 (6)
C6	0.0149 (7)	0.0164 (8)	0.0168 (8)	−0.0001 (6)	0.0008 (6)	−0.0014 (6)
C3	0.0164 (8)	0.0150 (8)	0.0157 (8)	−0.0010 (6)	0.0021 (6)	−0.0006 (6)
C4	0.0192 (8)	0.0168 (8)	0.0148 (8)	0.0010 (6)	0.0032 (6)	0.0011 (6)
C7	0.0212 (9)	0.0264 (10)	0.0152 (9)	−0.0009 (6)	−0.0029 (7)	0.0021 (6)
C5	0.0148 (8)	0.0181 (10)	0.0133 (9)	0.0027 (5)	0.0002 (7)	−0.0013 (5)
C2	0.0144 (8)	0.0134 (9)	0.0124 (8)	0.0027 (5)	−0.0000 (7)	−0.0018 (5)
C8	0.0159 (7)	0.0122 (8)	0.0151 (8)	−0.0011 (6)	0.0035 (6)	−0.0015 (6)

Geometric parameters (Å, º)

O2—C8	1.331 (2)	C6—C5	1.395 (3)
O2—H2	0.820	C6—H6	0.930
O1—C8	1.218 (2)	C3—C2	1.388 (3)
O3—H1W	0.820	C3—C4	1.393 (3)
O3—H2W	0.820	C3—H3	0.930
N1—C2	1.472 (3)	C4—C5	1.397 (3)
N1—H1C	0.890	C4—H4	0.930
N1—H1B	0.890	C7—C5	1.516 (3)
N1—H1A	0.890	C7—H7A	0.960
C1—C8	1.497 (3)	C7—H7B	0.960
C1—C2	1.405 (3)	C7—H7C	0.960
C1—C6	1.404 (3)
O2—C8—O1	123.7 (2)	C5—C4—H4	119.4
O2—C8—C1	112.4 (2)	C5—C7—H7A	109.5
O1—C8—C1	123.9 (2)	C5—C7—H7B	109.5
N1—C2—C1	121.7 (2)	C5—C7—H7C	109.5
N1—C2—C3	118.0 (1)	C2—N1—H1C	109.5
C1—C2—C3	120.3 (2)	C2—N1—H1B	109.5
C1—C6—C5	122.2 (2)	C2—N1—H1A	109.5
C1—C6—H6	118.9	C2—C1—C8	121.4 (1)
C6—C5—C4	117.9 (2)	C2—C3—H3	119.9
C6—C5—C7	120.9 (1)	C8—O2—H2	109.5
C6—C1—C8	120.3 (2)	H1A—N1—H1C	109.5
C6—C1—C2	118.3 (2)	H1A—N1—H1B	109.5
C3—C4—C5	121.2 (2)	H1C—N1—H1B	109.5
C3—C4—H4	119.4	H1W—O3—H2W	101.2
C4—C5—C7	121.3 (2)	H7B—C7—H7A	109.5
C4—C3—C2	120.1 (2)	H7B—C7—H7C	109.5
C4—C3—H3	119.9	H7C—C7—H7A	109.5
C5—C6—H6	118.9
O2—C8—C1—C2	−166.2 (1)	C6—C5—C7—H7C	−15.4
O2—C8—C1—C6	15.4 (1)	C6—C1—C2—C3	0.4 (1)
O1—C8—O2—H2	1.1	C3—C2—N1—H1C	109.3
O1—C8—C1—C2	14.5 (2)	C3—C2—N1—H1B	−10.7
O1—C8—C1—C6	−163.9 (1)	C3—C2—N1—H1A	−130.7
N1—C2—C1—C8	2.3 (1)	C3—C2—C1—C8	−178.1 (2)
N1—C2—C1—C6	−179.2 (1)	C3—C4—C5—C7	179.5 (2)
N1—C2—C3—C4	179.8 (2)	C4—C5—C6—H6	−179.8
N1—C2—C3—H3	−0.2	C4—C5—C7—H7A	−74.4
C1—C8—O2—H2	−178.2	C4—C5—C7—H7B	45.6
C1—C2—N1—H1C	−71.1	C4—C5—C7—H7C	165.6
C1—C2—N1—H1B	168.9	C7—C5—C6—H6	1.1
C1—C2—N1—H1A	48.9	C7—C5—C4—H4	−0.5
C1—C2—C3—C4	0.2 (2)	C5—C6—C1—C8	177.9 (2)
C1—C2—C3—H3	−179.8	C5—C6—C1—C2	−0.5 (2)
C1—C6—C5—C4	0.2 (2)	C5—C4—C3—C2	−0.6 (2)
C1—C6—C5—C7	−178.9 (2)	C5—C4—C3—H3	179.4
C6—C5—C4—C3	0.4 (2)	C2—C1—C6—H6	179.5
C6—C5—C4—H4	−179.6	C2—C3—C4—H4	179.4
C6—C5—C7—H7A	104.6	C8—C1—C6—H6	−2.1
C6—C5—C7—H7B	−135.4	H3—C3—C4—H4	−0.6