Tetra­butyl­ammonium hydrogen phenyl­arsonate–phenyl­arsonic acid (1/1)

Reck, L.; Schmitt, W.

doi:10.1107/S1600536812035362

metal-organic compounds

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ISSN: 2056-9890

Volume 68| Part 9| September 2012| Pages m1212-m1213

doi:10.1107/S1600536812035362

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Tetrabutylammonium hydrogen phenylarsonate–phenylarsonic acid (1/1)

Lukas Reck ^a and Wolfgang Schmitt ^a ^*

^aSchool of Chemistry, Trinity College, Dublin 2, Ireland
^*Correspondence e-mail: schmittw@tcd.ie

(Received 1 August 2012; accepted 9 August 2012; online 25 August 2012)

The structure of the title salt adduct, (C₄H₉)₄N⁺·C₆H₅AsO₃H⁻·C₆H₅AsO₃H₂, features chains along the a axis comprising alternating hydrogen phenylarsonate anions and phenylarsonic acid molecules linked by O—H⋯O hydrogen bonds.

Related literature

For similar structures containing bulky hydrophobic cations and hydrogen-bonded chains of hydrogen(arylphosphonate)/arylphosphonic acid, see: Clarke et al. (2005 ); Latham et al. (2007 , 2008 ). For hybrid organic–inorganic polyoxidometalate frameworks including arylarsonic acid ligands, see: Breen, Clérac et al. (2012 ); Breen, Zhang et al. (2012 ); Zhang & Schmitt (2011 ); Onet et al. (2011 ); Breen & Schmitt (2008 ).

Experimental

Crystal data

C₁₆H₃₆N⁺·C₆H₆AsO₃⁻·C₆H₇AsO₃
M_r = 645.52
Triclinic, $[P \overline 1]$
a = 9.035 (2) Å
b = 10.137 (3) Å
c = 18.789 (5) Å
α = 94.005 (5)°
β = 97.749 (4)°
γ = 114.289 (4)°
V = 1539.2 (7) Å³
Z = 2
Mo Kα radiation
μ = 2.21 mm⁻¹
T = 120 K
0.5 × 0.3 × 0.1 mm

Data collection

Bruker SMART APEX diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 1997 ) T_min = 0.291, T_max = 0.809
15253 measured reflections
7513 independent reflections
6769 reflections with I > 2σ(I)
R_int = 0.023

Refinement

R[F² > 2σ(F²)] = 0.026
wR(F²) = 0.070
S = 1.03
7513 reflections
530 parameters
All H-atom parameters refined
Δρ_max = 0.61 e Å⁻³
Δρ_min = −0.71 e Å⁻³

Table 1
Selected bond lengths (Å)

As1—O13	1.6625 (10)
As1—O12	1.6723 (11)
As1—O11	1.7279 (11)
As1—C11	1.9001 (16)
As2—O23	1.6432 (11)
As2—O22	1.7013 (11)
As2—O21	1.7030 (12)
As2—C21	1.9153 (16)

Table 2
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O11—H11⋯O23	0.77 (3)	1.88 (3)	2.6375 (17)	166 (3)
O21—H21⋯O13ⁱ	0.75 (3)	1.78 (3)	2.5280 (17)	176 (3)
O22—H22⋯O12ⁱ	0.93 (4)	1.57 (4)	2.4936 (17)	176 (4)
Symmetry code: (i) x-1, y, z.

Data collection: SMART (Bruker, 1997); cell refinement: SAINT (Bruker, 1997); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ) and OLEX2 (Dolomanov et al., 2009 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008) and OLEX2; molecular graphics: OLEX2; software used to prepare material for publication: SHELXL97 and OLEX2.

Supporting information

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536812035362/tk5138sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536812035362/tk5138Isup2.hkl

Supporting information file. DOI: 10.1107/S1600536812035362/tk5138Isup3.cdx

checkCIF report

Comment top

In the course of our studies on hybrid organic-inorganic polyoxometalate frameworks, including arylarsonic acid ligands (Breen, Clérac et al., 2012; Breen, Zhang et al., 2012; Zhang & Schmitt, 2011; Onet et al., 2011; Breen & Schmitt, 2008), we attempted to prepare tetrabutylammonium hydrogen phenylarsonate [(C₄H₉)₄N]⁺[C₆H₅AsO₃H]^- as a starting material for synthesis. Unexpectedly, mixing equimolar amounts of tetrabutylammonium hydroxide and phenylarsonic acid in aqueous solution and slow evaporation resulted in crystals with a 2:1 stoichiometry of tetrabutylammonium to phenylarsonic acid. We therefore undertook a closer structural examination of these crystals in order to find out if there is a structural reason for the apparent stability of this stoichiometry.

The structure consists of hydrogen-bonded chains of alternating hydrogen phenylarsonate anions and phenylarsonic acid molecules extending in the direction of the crystallographic a axis. These chains form two-dimensional sheets via π-π interactions that extend in the crystallographic (010) plane. The sheets alternate along the crystallographic b axis with layers consisting of tetrabutylammonium cations to form a lamellar structure. Analogous structures are known for salts with a 2:1 stoichiometry between a bulky organic monocation and phenylphosphonic acid (see Clarke et al., 2005, Latham et al., 2007 and Latham et al., 2008), but to our knowledge, this is the first time it has been reported for phenylarsonic acid.

The hydrogen phenylarsonate anion contains one long and two short As–O bonds, while the phenylarsonic acid molecule contains one short and two long As–O bonds (see Table 1). This is consistent with the assigned proton positions on these molecules: the As–O distance is shorter when the oxygen atom is unprotonated, as the formal bond order of these bonds is higher than that of bonds to protonated oxygen atoms.

Each hydrogen mphenylarsonate anion acts as a hydrogen acceptor for two very short hydrogen bonds from one neighbouring phenylarsonic acid molecule and as a hydrogen bond donor for a longer hydrogen bond to the other neighbouring phenylarsonic acid molecule (see Table 2, Figure 2).

π-π interactions are weak, with the centroid to centroid distance being 3.8669 (17) Å between the phenyl ring on the hydrogen mphenylarsonate anion and its closest symmetry equivalent and 4.0264 (17) Å between the phenyl ring on the phenylarsonic acid molecule and its closest symmetry equivalent.

We believe that the unexpected stoichiometry of the crystal is due to the balancing between hydrogen bond donors and acceptors: Hydrogen arsonate ions have two hydrogen bond acceptor sites and one hydrogen bond donor site, whereas arsonic acid molecules have two hydrogen bond donor sites and one hydrogen bond acceptor site, so that all sites with a potential for hydrogen bonding are saturated at a 1:1 stoichiometry between neutral acid and monodeprotonated anion. The resulting assembly is the least hydrophilic and therefore the first to crystallize from a concentrated aqueous solution containing a bulky hydrophobic cation.

Related literature top

For similar structures containing bulky hydrophobic cations and hydrogen-bonded chains of hydrogen(arylphosphonate)/arylphosphonic acid, see: Clarke et al. (2005); Latham et al. (2007, 2008). For hybrid organic–inorganic polyoxidometalate frameworks including arylarsonic acid ligands, see: Breen, Clérac et al. (2012); Breen, Zhang et al. (2012); Zhang & Schmitt (2011); Onet et al. (2011); Breen & Schmitt (2008).

Experimental top

Phenylarsonic acid (10 mmol, 2.02 g) was dissolved in 1 M aqueous tetrabutylammonium hydroxide solution (10 mmol, 10 ml). The colourless oil obtained by evaporation of the solution in vacuo formed large colourless crystals on standing at room temperature for 7 days.

Computing details top

Data collection: SMART (Bruker, 1997); cell refinement: SAINT (Bruker, 1997); data reduction: SAINT (Bruker, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008) and OLEX2 (Dolomanov et al., 2009); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008) and OLEX2 (Dolomanov et al., 2009); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and OLEX2 (Dolomanov et al., 2009).

Figures top

	Fig. 1. The asymmetric unit of the title compound, showing the numbering scheme and displacement ellipsoids on non-H atoms at the 50% probability level.
	Fig. 2. A hydrogen-bonded one-dimensional chain of alternating hydrogen phenylarsonate anions and phenylarsonic acid molecules. Phenyl rings (except for the carbon atom bound to As) and counterions have been omitted for clarity. Displacement ellipsoids on non-H atoms are drawn at the 50% probability level.

Tetrabutylammonium hydrogen phenylarsonate–phenylarsonic acid (1/1) top

Crystal data top

C₁₆H₃₆N⁺·C₆H₆AsO₃⁻·C₆H₇AsO₃	Z = 2
M_r = 645.52	F(000) = 676
Triclinic, P1	D_x = 1.393 Mg m⁻³
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 9.035 (2) Å	Cell parameters from 232 reflections
b = 10.137 (3) Å	θ = 2.3–27.2°
c = 18.789 (5) Å	µ = 2.21 mm⁻¹
α = 94.005 (5)°	T = 120 K
β = 97.749 (4)°	Block, colourless
γ = 114.289 (4)°	0.5 × 0.3 × 0.1 mm
V = 1539.2 (7) Å³

Data collection top

Bruker SMART APEX diffractometer	7513 independent reflections
Radiation source: fine-focus sealed tube	6769 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.023
ϕ and ω scans	θ_max = 28.3°, θ_min = 2.2°
Absorption correction: multi-scan (SADABS; Bruker, 1997)	h = −12→12
T_min = 0.291, T_max = 0.809	k = −13→13
15253 measured reflections	l = −23→24

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)] = 0.026	Hydrogen site location: difference Fourier map
wR(F²) = 0.070	All H-atom parameters refined
S = 1.03	w = 1/[σ²(F_o²) + (0.0421P)² + 0.2175P] where P = (F_o² + 2F_c²)/3
7513 reflections	(Δ/σ)_max = 0.001
530 parameters	Δρ_max = 0.61 e Å⁻³
0 restraints	Δρ_min = −0.71 e Å⁻³

Crystal data top

C₁₆H₃₆N⁺·C₆H₆AsO₃⁻·C₆H₇AsO₃	γ = 114.289 (4)°
M_r = 645.52	V = 1539.2 (7) Å³
Triclinic, P1	Z = 2
a = 9.035 (2) Å	Mo Kα radiation
b = 10.137 (3) Å	µ = 2.21 mm⁻¹
c = 18.789 (5) Å	T = 120 K
α = 94.005 (5)°	0.5 × 0.3 × 0.1 mm
β = 97.749 (4)°

Data collection top

Bruker SMART APEX diffractometer	7513 independent reflections
Absorption correction: multi-scan (SADABS; Bruker, 1997)	6769 reflections with I > 2σ(I)
T_min = 0.291, T_max = 0.809	R_int = 0.023
15253 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.026	0 restraints
wR(F²) = 0.070	All H-atom parameters refined
S = 1.03	Δρ_max = 0.61 e Å⁻³
7513 reflections	Δρ_min = −0.71 e Å⁻³
530 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
As1	0.983720 (17)	0.434497 (16)	0.191058 (8)	0.01665 (5)
O11	0.84503 (14)	0.41025 (14)	0.24937 (6)	0.0253 (2)
H11	0.799 (3)	0.458 (3)	0.2399 (15)	0.060 (8)*
O12	1.13065 (13)	0.60598 (11)	0.20887 (6)	0.0208 (2)
O13	1.05793 (13)	0.31108 (12)	0.20416 (6)	0.0218 (2)
N1	1.04658 (14)	0.94499 (13)	0.26111 (7)	0.0157 (2)
C11	0.86611 (17)	0.39575 (16)	0.09453 (8)	0.0193 (3)
C12	0.9186 (2)	0.33147 (18)	0.04140 (9)	0.0248 (3)
H12	1.011 (3)	0.312 (2)	0.0525 (12)	0.036 (5)*
C13	0.8426 (2)	0.3079 (2)	−0.02994 (10)	0.0301 (4)
H13	0.880 (2)	0.268 (2)	−0.0679 (11)	0.030 (5)*
C14	0.7155 (2)	0.3475 (2)	−0.04864 (10)	0.0322 (4)
H14	0.674 (3)	0.334 (2)	−0.0930 (12)	0.034 (6)*
C15	0.6630 (2)	0.4103 (2)	0.00444 (11)	0.0379 (4)
H15	0.571 (3)	0.437 (2)	−0.0117 (12)	0.044 (6)*
C16	0.7377 (2)	0.4351 (2)	0.07646 (10)	0.0292 (4)
H16	0.707 (3)	0.473 (2)	0.1076 (12)	0.034 (6)*
C31	1.06254 (18)	0.83454 (16)	0.30861 (8)	0.0171 (3)
H31A	0.950 (2)	0.764 (2)	0.3068 (10)	0.018 (4)*
H31B	1.115 (2)	0.790 (2)	0.2842 (10)	0.019 (4)*
C32	1.1517 (2)	0.89580 (18)	0.38583 (9)	0.0222 (3)
H32A	1.089 (2)	0.926 (2)	0.4123 (11)	0.026 (5)*
H32B	1.253 (2)	0.982 (2)	0.3874 (10)	0.021 (4)*
C33	1.1868 (2)	0.7791 (2)	0.42250 (10)	0.0281 (3)
H33A	1.261 (3)	0.751 (2)	0.3952 (12)	0.035 (5)*
H33B	1.241 (3)	0.822 (2)	0.4668 (12)	0.034 (5)*
C34	1.0341 (3)	0.6426 (2)	0.42641 (12)	0.0406 (5)
H34A	1.060 (3)	0.580 (3)	0.4569 (13)	0.045 (6)*
H34B	0.988 (3)	0.590 (3)	0.3788 (15)	0.050 (7)*
H34C	0.962 (3)	0.675 (2)	0.4455 (12)	0.038 (6)*
C41	0.93601 (17)	0.85567 (16)	0.19096 (8)	0.0167 (3)
H41A	0.835 (2)	0.799 (2)	0.2031 (9)	0.015 (4)*
H41B	0.984 (2)	0.7952 (19)	0.1749 (9)	0.014 (4)*
C42	0.90926 (19)	0.94151 (17)	0.13157 (8)	0.0199 (3)
H42A	0.870 (2)	1.012 (2)	0.1467 (10)	0.023 (5)*
H42B	1.014 (3)	1.004 (2)	0.1162 (12)	0.037 (6)*
C43	0.7900 (2)	0.8353 (2)	0.06719 (9)	0.0288 (3)
H43A	0.828 (3)	0.767 (3)	0.0487 (12)	0.044 (6)*
H43B	0.692 (3)	0.781 (3)	0.0840 (12)	0.039 (6)*
C44	0.7506 (2)	0.9096 (2)	0.00493 (10)	0.0334 (4)
H44A	0.677 (3)	0.839 (3)	−0.0324 (15)	0.054 (7)*
H44B	0.847 (3)	0.971 (3)	−0.0122 (13)	0.050 (7)*
H44C	0.698 (3)	0.973 (3)	0.0199 (13)	0.047 (6)*
C51	1.21333 (17)	1.05089 (16)	0.24719 (8)	0.0180 (3)
H51A	1.280 (2)	1.095 (2)	0.2939 (10)	0.018 (4)*
H51B	1.192 (2)	1.121 (2)	0.2232 (10)	0.016 (4)*
C52	1.30155 (18)	0.98468 (17)	0.20316 (9)	0.0209 (3)
H52A	1.237 (2)	0.947 (2)	0.1528 (11)	0.026 (5)*
H52B	1.310 (2)	0.904 (2)	0.2218 (11)	0.024 (5)*
C53	1.47142 (19)	1.10091 (18)	0.19840 (10)	0.0224 (3)
H53A	1.462 (2)	1.176 (2)	0.1776 (11)	0.027 (5)*
H53B	1.530 (2)	1.133 (2)	0.2446 (11)	0.022 (5)*
C54	1.5617 (2)	1.0398 (2)	0.15297 (11)	0.0288 (4)
H54A	1.664 (3)	1.110 (2)	0.1490 (12)	0.035 (5)*
H54B	1.506 (3)	1.010 (2)	0.1048 (13)	0.036 (6)*
H54C	1.567 (3)	0.956 (3)	0.1718 (13)	0.044 (6)*
C61	0.97536 (18)	1.03791 (16)	0.29762 (8)	0.0182 (3)
H61A	0.972 (2)	1.107 (2)	0.2659 (10)	0.017 (4)*
H61B	1.062 (2)	1.094 (2)	0.3409 (10)	0.018 (4)*
C62	0.81020 (19)	0.95365 (18)	0.31980 (9)	0.0213 (3)
H62A	0.810 (2)	0.882 (2)	0.3471 (11)	0.029 (5)*
H62B	0.725 (2)	0.900 (2)	0.2774 (11)	0.028 (5)*
C63	0.7615 (2)	1.0596 (2)	0.36162 (10)	0.0274 (3)
H63A	0.845 (3)	1.116 (2)	0.4042 (12)	0.037 (6)*
H63B	0.765 (3)	1.141 (3)	0.3339 (13)	0.041 (6)*
C64	0.5945 (2)	0.9811 (2)	0.38350 (11)	0.0338 (4)
H64A	0.559 (3)	1.040 (3)	0.4060 (13)	0.044 (6)*
H64B	0.599 (3)	0.917 (3)	0.4161 (16)	0.070 (9)*
H64C	0.512 (3)	0.928 (3)	0.3427 (13)	0.043 (6)*
As2	0.478325 (17)	0.517474 (16)	0.248301 (8)	0.01779 (5)
O21	0.34772 (15)	0.38567 (13)	0.17947 (6)	0.0231 (2)
H21	0.260 (4)	0.365 (3)	0.1849 (15)	0.062 (9)*
O22	0.42750 (14)	0.66150 (12)	0.24787 (7)	0.0251 (2)
H22	0.317 (5)	0.641 (4)	0.236 (2)	0.112 (13)*
O23	0.67109 (13)	0.56498 (13)	0.23897 (7)	0.0285 (3)
C21	0.43938 (19)	0.44095 (16)	0.33777 (8)	0.0211 (3)
C22	0.3014 (2)	0.4323 (2)	0.36604 (9)	0.0287 (3)
H22A	0.232 (3)	0.472 (2)	0.3414 (12)	0.037 (6)*
C23	0.2713 (3)	0.3712 (2)	0.42920 (11)	0.0416 (5)
H23	0.196 (4)	0.366 (4)	0.4490 (18)	0.081 (11)*
C24	0.3770 (3)	0.3205 (2)	0.46396 (11)	0.0476 (6)
H24	0.362 (3)	0.277 (3)	0.5068 (16)	0.066 (8)*
C25	0.5133 (3)	0.3297 (2)	0.43635 (11)	0.0456 (5)
H25	0.585 (3)	0.299 (3)	0.4570 (15)	0.059 (8)*
C26	0.5467 (2)	0.38999 (19)	0.37277 (10)	0.0312 (4)
H26	0.638 (3)	0.400 (2)	0.3565 (11)	0.031 (5)*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
As1	0.01668 (8)	0.01561 (8)	0.01751 (8)	0.00714 (6)	0.00178 (6)	0.00218 (6)
O11	0.0238 (5)	0.0326 (7)	0.0222 (6)	0.0133 (5)	0.0079 (4)	0.0065 (5)
O12	0.0195 (5)	0.0149 (5)	0.0273 (6)	0.0079 (4)	0.0016 (4)	−0.0001 (4)
O13	0.0214 (5)	0.0158 (5)	0.0293 (6)	0.0094 (4)	0.0017 (4)	0.0055 (4)
N1	0.0160 (5)	0.0137 (6)	0.0172 (6)	0.0061 (5)	0.0031 (4)	0.0024 (5)
C11	0.0193 (6)	0.0153 (7)	0.0198 (7)	0.0046 (6)	0.0014 (5)	0.0028 (6)
C12	0.0269 (7)	0.0247 (8)	0.0227 (8)	0.0115 (7)	0.0032 (6)	0.0018 (6)
C13	0.0365 (9)	0.0262 (9)	0.0222 (8)	0.0086 (7)	0.0055 (7)	−0.0014 (7)
C14	0.0342 (9)	0.0303 (9)	0.0210 (8)	0.0062 (7)	−0.0058 (7)	0.0014 (7)
C15	0.0343 (9)	0.0462 (11)	0.0337 (10)	0.0229 (9)	−0.0086 (8)	0.0001 (9)
C16	0.0276 (8)	0.0351 (9)	0.0263 (9)	0.0178 (7)	−0.0015 (7)	−0.0032 (7)
C31	0.0195 (6)	0.0144 (7)	0.0184 (7)	0.0080 (6)	0.0032 (5)	0.0036 (5)
C32	0.0258 (7)	0.0216 (8)	0.0187 (7)	0.0109 (7)	0.0002 (6)	0.0016 (6)
C33	0.0337 (9)	0.0297 (9)	0.0212 (8)	0.0151 (7)	−0.0009 (7)	0.0068 (7)
C34	0.0480 (11)	0.0385 (11)	0.0358 (11)	0.0149 (10)	0.0126 (9)	0.0215 (9)
C41	0.0168 (6)	0.0161 (7)	0.0157 (7)	0.0059 (6)	0.0019 (5)	0.0016 (5)
C42	0.0205 (7)	0.0211 (7)	0.0185 (7)	0.0089 (6)	0.0041 (6)	0.0045 (6)
C43	0.0336 (9)	0.0290 (9)	0.0204 (8)	0.0125 (8)	−0.0028 (7)	0.0023 (7)
C44	0.0339 (9)	0.0449 (11)	0.0219 (8)	0.0178 (9)	0.0008 (7)	0.0086 (8)
C51	0.0171 (6)	0.0135 (7)	0.0211 (7)	0.0043 (5)	0.0036 (5)	0.0025 (6)
C52	0.0171 (6)	0.0183 (7)	0.0263 (8)	0.0066 (6)	0.0049 (6)	0.0009 (6)
C53	0.0186 (7)	0.0187 (7)	0.0289 (9)	0.0066 (6)	0.0054 (6)	0.0038 (7)
C54	0.0220 (7)	0.0248 (8)	0.0429 (11)	0.0109 (7)	0.0125 (7)	0.0068 (8)
C61	0.0202 (6)	0.0162 (7)	0.0201 (7)	0.0093 (6)	0.0044 (6)	0.0019 (6)
C62	0.0210 (7)	0.0210 (7)	0.0246 (8)	0.0107 (6)	0.0065 (6)	0.0035 (6)
C63	0.0237 (7)	0.0305 (9)	0.0292 (9)	0.0140 (7)	0.0049 (7)	−0.0040 (7)
C64	0.0258 (8)	0.0432 (11)	0.0339 (10)	0.0170 (8)	0.0078 (7)	−0.0044 (9)
As2	0.01481 (8)	0.01589 (8)	0.02339 (9)	0.00662 (6)	0.00487 (6)	0.00389 (6)
O21	0.0246 (6)	0.0215 (6)	0.0224 (6)	0.0101 (5)	0.0022 (5)	0.0002 (4)
O22	0.0236 (5)	0.0161 (5)	0.0366 (7)	0.0103 (5)	0.0028 (5)	0.0032 (5)
O23	0.0171 (5)	0.0243 (6)	0.0462 (7)	0.0081 (5)	0.0123 (5)	0.0083 (5)
C21	0.0233 (7)	0.0153 (7)	0.0203 (7)	0.0056 (6)	−0.0006 (6)	0.0005 (6)
C22	0.0272 (8)	0.0300 (9)	0.0212 (8)	0.0054 (7)	0.0033 (6)	−0.0007 (7)
C23	0.0475 (11)	0.0354 (11)	0.0253 (9)	0.0002 (9)	0.0123 (9)	−0.0008 (8)
C24	0.0809 (16)	0.0269 (10)	0.0188 (9)	0.0090 (10)	0.0026 (10)	0.0033 (7)
C25	0.0738 (15)	0.0286 (10)	0.0294 (10)	0.0248 (11)	−0.0150 (10)	−0.0004 (8)
C26	0.0371 (9)	0.0228 (8)	0.0309 (9)	0.0147 (7)	−0.0062 (7)	−0.0015 (7)

Geometric parameters (Å, º) top

As1—O13	1.6625 (10)	C44—H44C	0.99 (2)
As1—O12	1.6723 (11)	C51—C52	1.520 (2)
As1—O11	1.7279 (11)	C51—H51A	0.956 (19)
As1—C11	1.9001 (16)	C51—H51B	0.941 (18)
O11—H11	0.77 (3)	C52—C53	1.522 (2)
N1—C41	1.5130 (18)	C52—H52A	1.00 (2)
N1—C61	1.5163 (17)	C52—H52B	0.94 (2)
N1—C51	1.5185 (18)	C53—C54	1.519 (2)
N1—C31	1.5194 (18)	C53—H53A	0.91 (2)
C11—C16	1.383 (2)	C53—H53B	0.91 (2)
C11—C12	1.392 (2)	C54—H54A	0.92 (2)
C12—C13	1.378 (2)	C54—H54B	0.94 (2)
C12—H12	0.94 (2)	C54—H54C	0.96 (2)
C13—C14	1.376 (3)	C61—C62	1.516 (2)
C13—H13	0.96 (2)	C61—H61A	0.954 (18)
C14—C15	1.383 (3)	C61—H61B	1.000 (18)
C14—H14	0.84 (2)	C62—C63	1.526 (2)
C15—C16	1.384 (3)	C62—H62A	0.92 (2)
C15—H15	1.00 (2)	C62—H62B	0.97 (2)
C16—H16	0.82 (2)	C63—C64	1.518 (2)
C31—C32	1.512 (2)	C63—H63A	0.98 (2)
C31—H31A	0.966 (19)	C63—H63B	1.00 (2)
C31—H31B	0.922 (18)	C64—H64A	0.89 (2)
C32—C33	1.529 (2)	C64—H64B	0.93 (3)
C32—H32A	0.929 (19)	C64—H64C	0.94 (2)
C32—H32B	0.96 (2)	As2—O23	1.6432 (11)
C33—C34	1.515 (3)	As2—O22	1.7013 (11)
C33—H33A	1.01 (2)	As2—O21	1.7030 (12)
C33—H33B	0.89 (2)	As2—C21	1.9153 (16)
C34—H34A	0.96 (3)	O21—H21	0.75 (3)
C34—H34B	0.95 (3)	O22—H22	0.93 (4)
C34—H34C	0.94 (2)	C21—C26	1.388 (2)
C41—C42	1.515 (2)	C21—C22	1.393 (2)
C41—H41A	0.930 (18)	C22—C23	1.385 (3)
C41—H41B	0.943 (17)	C22—H22A	0.96 (2)
C42—C43	1.515 (2)	C23—C24	1.372 (4)
C42—H42A	0.964 (19)	C23—H23	0.81 (3)
C42—H42B	1.00 (2)	C24—C25	1.371 (4)
C43—C44	1.515 (2)	C24—H24	0.94 (3)
C43—H43A	0.95 (2)	C25—C26	1.392 (3)
C43—H43B	0.94 (2)	C25—H25	0.88 (3)
C44—H44A	0.93 (3)	C26—H26	0.89 (2)
C44—H44B	0.95 (3)

O13—As1—O12	112.71 (6)	H44A—C44—H44C	108 (2)
O13—As1—O11	106.12 (6)	H44B—C44—H44C	106 (2)
O12—As1—O11	109.42 (6)	N1—C51—C52	115.86 (12)
O13—As1—C11	109.58 (6)	N1—C51—H51A	106.0 (11)
O12—As1—C11	110.72 (6)	C52—C51—H51A	109.5 (10)
O11—As1—C11	108.09 (6)	N1—C51—H51B	104.9 (11)
As1—O11—H11	108 (2)	C52—C51—H51B	110.5 (10)
C41—N1—C61	111.98 (11)	H51A—C51—H51B	109.9 (15)
C41—N1—C51	110.79 (11)	C51—C52—C53	109.94 (12)
C61—N1—C51	105.97 (11)	C51—C52—H52A	109.8 (10)
C41—N1—C31	105.49 (11)	C53—C52—H52A	108.1 (11)
C61—N1—C31	111.07 (11)	C51—C52—H52B	112.6 (12)
C51—N1—C31	111.65 (11)	C53—C52—H52B	110.7 (12)
C16—C11—C12	120.67 (15)	H52A—C52—H52B	105.6 (16)
C16—C11—As1	121.87 (12)	C54—C53—C52	111.50 (14)
C12—C11—As1	117.40 (11)	C54—C53—H53A	107.9 (12)
C13—C12—C11	119.57 (15)	C52—C53—H53A	110.2 (12)
C13—C12—H12	119.0 (13)	C54—C53—H53B	109.1 (11)
C11—C12—H12	121.2 (13)	C52—C53—H53B	107.3 (12)
C14—C13—C12	120.28 (16)	H53A—C53—H53B	110.8 (17)
C14—C13—H13	118.4 (12)	C53—C54—H54A	112.0 (13)
C12—C13—H13	121.2 (12)	C53—C54—H54B	111.1 (13)
C13—C14—C15	119.90 (17)	H54A—C54—H54B	103.3 (19)
C13—C14—H14	117.8 (14)	C53—C54—H54C	109.8 (14)
C15—C14—H14	122.3 (14)	H54A—C54—H54C	112.9 (19)
C14—C15—C16	120.79 (17)	H54B—C54—H54C	107.5 (19)
C14—C15—H15	117.1 (13)	C62—C61—N1	115.27 (12)
C16—C15—H15	122.1 (13)	C62—C61—H61A	112.6 (10)
C11—C16—C15	118.79 (16)	N1—C61—H61A	106.8 (10)
C11—C16—H16	120.8 (15)	C62—C61—H61B	111.0 (10)
C15—C16—H16	120.4 (15)	N1—C61—H61B	103.2 (10)
C32—C31—N1	115.79 (12)	H61A—C61—H61B	107.2 (15)
C32—C31—H31A	111.6 (11)	C61—C62—C63	109.42 (13)
N1—C31—H31A	104.5 (11)	C61—C62—H62A	112.9 (12)
C32—C31—H31B	111.6 (11)	C63—C62—H62A	110.1 (12)
N1—C31—H31B	104.9 (11)	C61—C62—H62B	110.8 (12)
H31A—C31—H31B	107.8 (15)	C63—C62—H62B	109.8 (11)
C31—C32—C33	109.85 (13)	H62A—C62—H62B	103.7 (17)
C31—C32—H32A	110.9 (12)	C64—C63—C62	111.56 (15)
C33—C32—H32A	108.9 (12)	C64—C63—H63A	110.2 (13)
C31—C32—H32B	111.2 (11)	C62—C63—H63A	112.0 (12)
C33—C32—H32B	110.5 (11)	C64—C63—H63B	111.4 (13)
H32A—C32—H32B	105.5 (16)	C62—C63—H63B	111.7 (13)
C34—C33—C32	114.41 (15)	H63A—C63—H63B	99.4 (18)
C34—C33—H33A	109.1 (12)	C63—C64—H64A	114.5 (16)
C32—C33—H33A	108.3 (12)	C63—C64—H64B	110.2 (17)
C34—C33—H33B	110.2 (14)	H64A—C64—H64B	105 (2)
C32—C33—H33B	105.8 (14)	C63—C64—H64C	111.0 (14)
H33A—C33—H33B	108.9 (18)	H64A—C64—H64C	106 (2)
C33—C34—H34A	111.7 (14)	H64B—C64—H64C	109 (2)
C33—C34—H34B	108.6 (15)	O23—As2—O22	111.86 (6)
H34A—C34—H34B	108 (2)	O23—As2—O21	110.46 (6)
C33—C34—H34C	105.8 (14)	O22—As2—O21	107.93 (6)
H34A—C34—H34C	110 (2)	O23—As2—C21	110.94 (7)
H34B—C34—H34C	112 (2)	O22—As2—C21	107.65 (6)
N1—C41—C42	116.09 (12)	O21—As2—C21	107.84 (6)
N1—C41—H41A	106.0 (11)	As2—O21—H21	109 (2)
C42—C41—H41A	108.8 (11)	As2—O22—H22	118 (2)
N1—C41—H41B	105.8 (10)	C26—C21—C22	120.47 (17)
C42—C41—H41B	110.2 (10)	C26—C21—As2	119.45 (13)
H41A—C41—H41B	109.8 (15)	C22—C21—As2	120.05 (12)
C43—C42—C41	108.80 (13)	C23—C22—C21	119.34 (18)
C43—C42—H42A	110.4 (11)	C23—C22—H22A	122.5 (13)
C41—C42—H42A	113.6 (11)	C21—C22—H22A	118.1 (13)
C43—C42—H42B	109.7 (13)	C24—C23—C22	120.4 (2)
C41—C42—H42B	112.0 (13)	C24—C23—H23	116 (2)
H42A—C42—H42B	102.2 (17)	C22—C23—H23	124 (2)
C44—C43—C42	113.39 (16)	C25—C24—C23	120.3 (2)
C44—C43—H43A	107.8 (14)	C25—C24—H24	115.5 (17)
C42—C43—H43A	112.9 (14)	C23—C24—H24	124.2 (17)
C44—C43—H43B	108.8 (14)	C24—C25—C26	120.7 (2)
C42—C43—H43B	106.7 (14)	C24—C25—H25	123.4 (18)
H43A—C43—H43B	106.9 (19)	C26—C25—H25	115.9 (18)
C43—C44—H44A	109.2 (16)	C21—C26—C25	118.77 (19)
C43—C44—H44B	112.1 (15)	C21—C26—H26	120.8 (14)
H44A—C44—H44B	110 (2)	C25—C26—H26	120.3 (14)
C43—C44—H44C	111.2 (14)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O11—H11···O23	0.77 (3)	1.88 (3)	2.6375 (17)	166 (3)
O21—H21···O13ⁱ	0.75 (3)	1.78 (3)	2.5280 (17)	176 (3)
O22—H22···O12ⁱ	0.93 (4)	1.57 (4)	2.4936 (17)	176 (4)

Symmetry code: (i) x−1, y, z.

Experimental details

Crystal data
Chemical formula	C₁₆H₃₆N⁺·C₆H₆AsO₃⁻·C₆H₇AsO₃
M_r	645.52
Crystal system, space group	Triclinic, P1
Temperature (K)	120
a, b, c (Å)	9.035 (2), 10.137 (3), 18.789 (5)
α, β, γ (°)	94.005 (5), 97.749 (4), 114.289 (4)
V (Å³)	1539.2 (7)
Z	2
Radiation type	Mo Kα
µ (mm⁻¹)	2.21
Crystal size (mm)	0.5 × 0.3 × 0.1

Data collection
Diffractometer	Bruker SMART APEX diffractometer
Absorption correction	Multi-scan (SADABS; Bruker, 1997)
T_min, T_max	0.291, 0.809
No. of measured, independent and observed [I > 2σ(I)] reflections	15253, 7513, 6769
R_int	0.023
(sin θ/λ)_max (Å⁻¹)	0.667

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.026, 0.070, 1.03
No. of reflections	7513
No. of parameters	530
H-atom treatment	All H-atom parameters refined
Δρ_max, Δρ_min (e Å⁻³)	0.61, −0.71

Computer programs: SMART (Bruker, 1997), SAINT (Bruker, 1997), SHELXS97 (Sheldrick, 2008) and OLEX2 (Dolomanov et al., 2009), SHELXL97 (Sheldrick, 2008) and OLEX2 (Dolomanov et al., 2009), OLEX2 (Dolomanov et al., 2009).

Selected bond lengths (Å) top

As1—O13	1.6625 (10)	As2—O23	1.6432 (11)
As1—O12	1.6723 (11)	As2—O22	1.7013 (11)
As1—O11	1.7279 (11)	As2—O21	1.7030 (12)
As1—C11	1.9001 (16)	As2—C21	1.9153 (16)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O11—H11···O23	0.77 (3)	1.88 (3)	2.6375 (17)	166 (3)
O21—H21···O13ⁱ	0.75 (3)	1.78 (3)	2.5280 (17)	176 (3)
O22—H22···O12ⁱ	0.93 (4)	1.57 (4)	2.4936 (17)	176 (4)

Symmetry code: (i) x−1, y, z.

Acknowledgements

The authors thank the Science Foundation Ireland (SFI) for financial support (grant No. 08/IN.1/I2047). LR gratefully acknowledges financial support from Trinity College Dublin through an Ussher Fellowship award.

References

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