The monoclinic polymorph of dimethyl­arsinic acid

Betz, R.; McCleland, C.; Marchand, H.

doi:10.1107/S1600536811025505

metal-organic compounds

CRYSTALLOGRAPHIC
COMMUNICATIONS

ISSN: 2056-9890

Volume 67| Part 8| August 2011| Page m1013

doi:10.1107/S1600536811025505

Open

access

The monoclinic polymorph of dimethylarsinic acid

Richard Betz,^a ^* Cedric McCleland ^a and Harold Marchand ^a

^aNelson Mandela Metropolitan University, Summerstrand Campus, Department of Chemistry, University Way, Summerstrand, PO Box 77000, Port Elizabeth 6031, South Africa
^*Correspondence e-mail: richard.betz@webmail.co.za

(Received 21 June 2011; accepted 28 June 2011; online 2 July 2011)

The title compound, C₂H₇AsO₂ or [As(CH₃)₂O(OH)], is an organic derivative of arsinic acid, and is also known by its trivial name cacodylic acid. In contrast to the first polymorph (triclinic, space group P $[\overline{1}]$ , Z = 2), the current study revealed monoclinic symmetry (space group C2/c, Z = 8) for the second polymorph. The configuration of the tetrahedral molecule shows approximate C_s symmetry. Strong O—H⋯O hydrogen bonds connect the molecules to infinite zigzag chains along [010], which are further connected by weak intermolecular C—H⋯O contacts into a three-dimensional network.

Related literature

For the crystal structure of the triclinic polymorph of the title compound, see: Trotter & Zobel (1965 ). For graph-set analysis of hydrogen bonds, see: Etter et al. (1990 ); Bernstein et al. (1995 ).

Experimental

Crystal data

[As(CH₃)₂O(OH)]
M_r = 138.00
Monoclinic, C 2/c
a = 15.764 (9) Å
b = 6.494 (5) Å
c = 11.302 (4) Å
β = 125.86 (3)°
V = 937.7 (10) Å³
Z = 8
Mo Kα radiation
μ = 7.09 mm⁻¹
T = 200 K
0.49 × 0.42 × 0.39 mm

Data collection

Bruker APEXII CCD diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2008 ) T_min = 0.608, T_max = 1.000
7792 measured reflections
1166 independent reflections
1117 reflections with I > 2σ(I)
R_int = 0.040

Refinement

R[F² > 2σ(F²)] = 0.020
wR(F²) = 0.055
S = 1.20
1166 reflections
49 parameters
H-atom parameters constrained
Δρ_max = 0.31 e Å⁻³
Δρ_min = −0.80 e Å⁻³

Table 1
Selected bond lengths (Å)

As1—O2	1.6617 (19)
As1—O1	1.7201 (19)
As1—C2	1.895 (2)
As1—C1	1.895 (2)

Table 2
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1—H1⋯O2ⁱ	0.84	1.69	2.528 (2)	172
C1—H1A⋯O2ⁱⁱ	0.98	2.52	3.481 (3)	167
C2—H2B⋯O1ⁱⁱⁱ	0.98	2.48	3.354 (3)	148
Symmetry codes: (i) $[-x+{\script{1\over 2}}, y+{\script{1\over 2}}, -z+{\script{1\over 2}}]$ ; (ii) $[-x+{\script{1\over 2}}, -y+{\script{1\over 2}}, -z+1]$ ; (iii) -x+1, -y+1, -z+1.

Data collection: APEX2 (Bruker, 2010 ); cell refinement: SAINT (Bruker, 2010); data reduction: SAINT; 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 Mercury (Macrae et al., 2008 ); software used to prepare material for publication: SHELXL97 and PLATON (Spek, 2009 ).

Supporting information

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536811025505/wm2504sup1.cif

Supporting information file. DOI: 10.1107/S1600536811025505/wm2504Isup2.cdx

Structure factors: contains datablock I. DOI: 10.1107/S1600536811025505/wm2504Isup3.hkl

Supporting information file. DOI: 10.1107/S1600536811025505/wm2504Isup4.cml

checkCIF report

Comment top

The precipitation of amines from their respective organic synthesis mixtures as the ammonium salts of inorganic acids is a common practice for obtaining and purifying the desired products. However, for a couple of higher-alkylated amines, the viability of this class of compounds as phase-transfer catalysts becomes troublesome with respect to their persistent solubility which is detrimental for achieving quantitative yields following this simple synthetic protocol. Decreasing the solubility of a protonated amine can be done upon variation of the counterion which may allow for a better packing and more pronounced intermolecular interactions in the solid state. Since we intended to perform a comprehensive study involving a variety of higher-alkylated amines, we set out to optimize the yield of several established synthesis procedures by variation of the acid used for precipitation. To allow for a rationalization and tailoring of the counterions to be preferred, we determined the crystal structure of the title compound to enable comparative studies in isolated, crystalline precipitates. The crystal structure of the title compound has been determined previously (Trotter & Zobel (1965)). However, a different crystal system (triclinic, space group P1, Z = 2) was reported, suggesting that the title compound is polymorphic. Moreover, hydrogen atoms were not included in the previous refinement procedure.

The length of the As–O-bonds show a marked difference with the formal As–O-double bond being shorter by about 0.06 Å than the corresponding single bond. A projection of both methyl groups along the C—C-axis shows their hydrogen atoms to adopt an ecliptic conformation (Fig. 1).

In the crystal structure, O—H···O hydrogen bonds as well as intermolecular C—H···O contacts, whose range falls by about 0.2 Å below the sum of the van-der-Waals radii of the atoms participating, are present. The hydrogen bonds are formed between the H atom of the hydroxyl group as donor and the formally double-bonded oxygen atom and connect the molecules to zigzag chains along [010]. The C—H···O contacts are supported by one hydrogen atom per methyl group each as the donor atom. While for one methyl group the double bonded O atom acts as acceptor and gives rise to the formation of centrosymmetric cacodylic acid dimers, the oxygen atom of the hydroxyl group acts as acceptor for the other methyl group. In this case, too, the formation of centrosymmetric cacodylic acid dimers can be observed. In total, the molecules are connected to a three-dimensional network in the crystal structure. In terms of graph-set analysis (Etter et al. (1990); Bernstein et al. (1995)), the descriptor for the classical hydrogen bonds is C¹₁(4) on the unitary level while both C—H···O contacts necessitate a R²₂(8) descriptor on the same level (Fig. 2).

The packing of the title compound in the crystal structure is shown in Figure 3.

Related literature top

For the crystal structure of the triclinic polymorph of the title compound, see: Trotter & Zobel (1965). For graph-set analysis of hydrogen bonds, see: Etter et al. (1990); Bernstein et al. (1995).

Experimental top

The compound was obtained commercially (KEK). Crystals suitable for the X-ray diffraction study were taken directly from the provided product.

Computing details top

Data collection: APEX2 (Bruker, 2010); cell refinement: SAINT (Bruker, 2010); data reduction: SAINT (Bruker, 2010); 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 Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and PLATON (Spek, 2009).

Figures top

	Fig. 1. The molecular structure of the title compound, with atom labels and anisotropic displacement ellipsoids drawn at the 50% probability level.
	Fig. 2. Intermolecular contacts, viewed along [001]. Blue dashed lines indicate classical O–H···O hydrogen bonds, green dashed lines C—H···O contacts. Symmetry operators: i) -x + 1/2, -y + 1/2, -z + 1; ii) -x + 1/2, y - 1/2, -z + 1/2; iii) -x + 1/2, y + 1/2, -z + 1/2; iv) -x + 1, -y + 1, -z + 1.
	Fig. 3. Molecular packing of the title compound, viewed along [010]; anisotropic displacement ellipsoids are drawn at the 50% probability level.

dimethylarsinic acid top

Crystal data top

[As(CH₃)₂O(OH)]	F(000) = 544
M_r = 138.00	D_x = 1.955 Mg m⁻³
Monoclinic, C2/c	Melting point = 468–469 K
Hall symbol: -C 2yc	Mo Kα radiation, λ = 0.71069 Å
a = 15.764 (9) Å	Cell parameters from 6920 reflections
b = 6.494 (5) Å	θ = 2.2–28.4°
c = 11.302 (4) Å	µ = 7.09 mm⁻¹
β = 125.86 (3)°	T = 200 K
V = 937.7 (10) Å³	Block, colourless
Z = 8	0.49 × 0.42 × 0.39 mm

Data collection top

Bruker APEXII CCD diffractometer	1166 independent reflections
Radiation source: fine-focus sealed tube	1117 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.040
ϕ and ω scans	θ_max = 28.4°, θ_min = 3.5°
Absorption correction: multi-scan (SADABS; Bruker, 2008)	h = −20→20
T_min = 0.608, T_max = 1.000	k = −8→7
7792 measured reflections	l = −15→15

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)] = 0.020	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.055	H-atom parameters constrained
S = 1.20	w = 1/[σ²(F_o²) + (0.0242P)² + 1.2973P] where P = (F_o² + 2F_c²)/3
1166 reflections	(Δ/σ)_max = 0.001
49 parameters	Δρ_max = 0.31 e Å⁻³
0 restraints	Δρ_min = −0.80 e Å⁻³

Crystal data top

[As(CH₃)₂O(OH)]	V = 937.7 (10) Å³
M_r = 138.00	Z = 8
Monoclinic, C2/c	Mo Kα radiation
a = 15.764 (9) Å	µ = 7.09 mm⁻¹
b = 6.494 (5) Å	T = 200 K
c = 11.302 (4) Å	0.49 × 0.42 × 0.39 mm
β = 125.86 (3)°

Data collection top

Bruker APEXII CCD diffractometer	1166 independent reflections
Absorption correction: multi-scan (SADABS; Bruker, 2008)	1117 reflections with I > 2σ(I)
T_min = 0.608, T_max = 1.000	R_int = 0.040
7792 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.020	0 restraints
wR(F²) = 0.055	H-atom parameters constrained
S = 1.20	Δρ_max = 0.31 e Å⁻³
1166 reflections	Δρ_min = −0.80 e Å⁻³
49 parameters

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

	x	y	z	U_iso*/U_eq
As1	0.338221 (14)	0.33757 (3)	0.373791 (19)	0.01723 (9)
O1	0.37470 (13)	0.5820 (2)	0.44526 (17)	0.0268 (3)
H1	0.3510	0.6676	0.3770	0.040*
O2	0.20889 (12)	0.3139 (2)	0.27582 (18)	0.0260 (3)
C1	0.4078 (2)	0.1666 (3)	0.5414 (3)	0.0293 (5)
H1A	0.3803	0.1934	0.5985	0.044*
H1B	0.4830	0.1961	0.6013	0.044*
H1C	0.3961	0.0218	0.5113	0.044*
C2	0.38735 (18)	0.2918 (4)	0.2580 (2)	0.0270 (4)
H2A	0.3738	0.1485	0.2243	0.041*
H2B	0.4628	0.3188	0.3162	0.041*
H2C	0.3509	0.3843	0.1734	0.041*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
As1	0.01664 (13)	0.01855 (13)	0.01733 (13)	0.00089 (6)	0.01041 (10)	−0.00034 (6)
O1	0.0276 (8)	0.0202 (7)	0.0229 (7)	−0.0003 (6)	0.0092 (6)	−0.0043 (6)
O2	0.0164 (7)	0.0298 (8)	0.0314 (8)	−0.0006 (6)	0.0137 (7)	−0.0059 (6)
C1	0.0327 (12)	0.0311 (12)	0.0269 (11)	0.0066 (9)	0.0189 (10)	0.0092 (8)
C2	0.0269 (11)	0.0353 (11)	0.0279 (10)	−0.0045 (9)	0.0211 (9)	−0.0053 (9)

Geometric parameters (Å, º) top

As1—O2	1.6617 (19)	C1—H1B	0.9800
As1—O1	1.7201 (19)	C1—H1C	0.9800
As1—C2	1.895 (2)	C2—H2A	0.9800
As1—C1	1.895 (2)	C2—H2B	0.9800
O1—H1	0.8400	C2—H2C	0.9800
C1—H1A	0.9800

O2—As1—O1	109.90 (8)	As1—C1—H1C	109.5
O2—As1—C2	111.32 (10)	H1A—C1—H1C	109.5
O1—As1—C2	108.04 (9)	H1B—C1—H1C	109.5
O2—As1—C1	112.19 (10)	As1—C2—H2A	109.5
O1—As1—C1	103.46 (10)	As1—C2—H2B	109.5
C2—As1—C1	111.56 (11)	H2A—C2—H2B	109.5
As1—O1—H1	109.5	As1—C2—H2C	109.5
As1—C1—H1A	109.5	H2A—C2—H2C	109.5
As1—C1—H1B	109.5	H2B—C2—H2C	109.5
H1A—C1—H1B	109.5

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···O2ⁱ	0.84	1.69	2.528 (2)	172
C1—H1A···O2ⁱⁱ	0.98	2.52	3.481 (3)	167
C2—H2B···O1ⁱⁱⁱ	0.98	2.48	3.354 (3)	148

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

Experimental details

Crystal data
Chemical formula	[As(CH₃)₂O(OH)]
M_r	138.00
Crystal system, space group	Monoclinic, C2/c
Temperature (K)	200
a, b, c (Å)	15.764 (9), 6.494 (5), 11.302 (4)
β (°)	125.86 (3)
V (Å³)	937.7 (10)
Z	8
Radiation type	Mo Kα
µ (mm⁻¹)	7.09
Crystal size (mm)	0.49 × 0.42 × 0.39

Data collection
Diffractometer	Bruker APEXII CCD diffractometer
Absorption correction	Multi-scan (SADABS; Bruker, 2008)
T_min, T_max	0.608, 1.000
No. of measured, independent and observed [I > 2σ(I)] reflections	7792, 1166, 1117
R_int	0.040
(sin θ/λ)_max (Å⁻¹)	0.668

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.020, 0.055, 1.20
No. of reflections	1166
No. of parameters	49
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.31, −0.80

Computer programs: APEX2 (Bruker, 2010), SAINT (Bruker, 2010), SHELXS97 (Sheldrick, 2008), ORTEP-3 (Farrugia, 1997) and Mercury (Macrae et al., 2008), SHELXL97 (Sheldrick, 2008) and PLATON (Spek, 2009).

Selected bond lengths (Å) top

As1—O2	1.6617 (19)	As1—C2	1.895 (2)
As1—O1	1.7201 (19)	As1—C1	1.895 (2)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···O2ⁱ	0.84	1.69	2.528 (2)	172
C1—H1A···O2ⁱⁱ	0.98	2.52	3.481 (3)	167
C2—H2B···O1ⁱⁱⁱ	0.98	2.48	3.354 (3)	148

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

Acknowledgements

The authors thank Mr Eric Bashman for helpful discussions.

References

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
Bruker (2008). SADABS. Bruker Inc., Madison, Wisconsin, USA. Google Scholar
Bruker (2010). APEX2 and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Etter, M. C., MacDonald, J. C. & Bernstein, J. (1990). Acta Cryst. B46, 256–262. CrossRef CAS Web of Science IUCr Journals Google Scholar
Farrugia, L. J. (1997). J. Appl. Cryst. 30, 565. CrossRef IUCr Journals Google Scholar
Macrae, C. F., Bruno, I. J., Chisholm, J. A., Edgington, P. R., McCabe, P., Pidcock, E., Rodriguez-Monge, L., Taylor, R., van de Streek, J. & Wood, P. A. (2008). J. Appl. Cryst. 41, 466–470. Web of Science CrossRef CAS IUCr Journals Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Spek, A. L. (2009). Acta Cryst. D65, 148–155. Web of Science CrossRef CAS IUCr Journals Google Scholar
Trotter, J. & Zobel, T. (1965). J. Chem. Soc. pp. 4466–4471. CrossRef Web of Science Google Scholar