2-Methyl­piperazinium bis­(dihydrogenarsenate)

Wilkinson, H.S.; Harrison, W.T.A.

doi:10.1107/S1600536807008392

metal-organic compounds

CRYSTALLOGRAPHIC
COMMUNICATIONS

ISSN: 2056-9890

Volume 63| Part 3| March 2007| Pages m900-m901

https://doi.org/10.1107/S1600536807008392

2-Methylpiperazinium bis(dihydrogenarsenate)

Hazel S. Wilkinson ^a and William T. A. Harrison ^a ^*

^aDepartment of Chemistry, University of Aberdeen, Meston Walk, Aberdeen AB24 3UE, Scotland
^*Correspondence e-mail: w.harrison@abdn.ac.uk

(Received 19 February 2007; accepted 19 February 2007; online 28 February 2007)

The title compound, C₅H₁₄N₂²⁺·2H₂AsO₄⁻, contains a network of centrosymmetric doubly protonated 2-methylpiperazinium cations, showing disorder of the methyl group, accompanied by dihydogenarsenate anions. The component species interact by way of cation-to-anion N—H⋯O and anion-to-anion O—H⋯O hydrogen bonds, the latter leading to infinite sheets of the H₂AsO₄⁻ anions containing R₆⁶(24) supramolecular loops.

Comment

The title compound, (I) (Fig. 1), was prepared as part of our ongoing studies of hydrogen-bonding interactions in the molecular salts of oxo-anions (Wilkinson & Harrison, 2007 ).

The tetrahedral H₂AsO₄⁻ anion in (I) [mean As—O = 1.677 (2) Å], shows the usual distinction (Table 1) between protonated and unprotonated As—O bond lengths (Wilkinson & Harrison, 2007). The complete 2-methylpiperazinium dication is generated by inversion. This must result in disorder, as each dication is chiral at C2. Thus, the two enantiomers are superimposed in the long-range structure of the crystal, with all the atoms of the ring overlapped. A typical chair conformation for the six-membered ring arises, and atom C3 of the methyl group is equatorial to the ring in both disorder components.

As well as Coulombic forces, the component species in (I) interact by way of a network of anion-to-anion O—H⋯O and cation-to-anion N—H⋯O hydrogen bonds (Table 2). The hydrogen-bonding scheme and overall structure in (I) are very similar to those in piperazinium bis(dihydrogenarsenate), (II) (Wilkinson & Harrison, 2007). In both (I) and (II), the H₂AsO₄⁻ units are linked into infinite (100) layers by the O—H⋯O bonds. A distinctive feature of the sheets are supramolecular R₆⁶(24) rings (Bernstein et al., 1995 ) built up from six tetrahedra, the rings being stabilized by N—H⋯O bonds from the organic cations (Fig. 2). For the two inter-tetrahedral O—H⋯O interactions, the As⋯Asⁱ and As⋯Asⁱⁱ (see Table 2 for symmetry codes) separations for (I) are 4.3061 (3) and 4.7599 (3) Å, respectively, which are distinctly different from the values of 4.0148 (3) and 5.0190 (3) Å for the topologically equivalent network in (II).

Figure 1
The molecular structure of (I)

(50% displacement ellipsoids and H atoms are drawn as spheres of arbitrary radius). The hydrogen bond is indicated by a double-dashed line. Only one disorder component of the cation is shown. [Symmetry code: (iv) −x, −y, 1 - z.]

Figure 2
Detail of a six-membered ring of H₂AsO₄⁻ groups in (I)

, in polyhedral representation, with attached organic cations. Only one disorder component of each cation is shown and the C-bound H atoms are omitted for clarity. The H⋯O parts of the O—H⋯O hydrogen bonds are coloured yellow and the H⋯O parts of the N—H⋯O hydrogen bonds are light blue. The As1* and As1# tetrahedra are generated by the symmetry operations (1 − x, 1 − y, 1 − z) and (1 − x, $[{1\over 2}]$ + y, $[{3\over 2}]$ − z), respectively.

Experimental

To an aqueous racemic 2-methylpiperazine solution (10 ml, 0.5 M) was added an aqueous H₃AsO₄ solution (10 ml, 0.5 M), resulting in a clear solution. Chunks and blocks of (I) grew as the water evaporated over the course of a few days; these were harvested by vacuum filtration and rinsed with acetone.

Crystal data

C₅H₁₄N₂²⁺·2AsH₂O₄⁻
M_r = 384.06
Monoclinic, P 2₁ /c
a = 6.7537 (3) Å
b = 8.1753 (4) Å
c = 12.7105 (5) Å
β = 107.501 (2)°
V = 669.31 (5) Å³
Z = 2
Mo Kα radiation
μ = 5.02 mm⁻¹
T = 293 (2) K
0.37 × 0.12 × 0.03 mm

Data collection

Bruker SMART 1000 CCD diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 1999 ) T_min = 0.258, T_max = 0.864
6913 measured reflections
2409 independent reflections
1929 reflections with I > 2σ(I)
R_int = 0.026

Refinement

R[F² > 2σ(F²)] = 0.029
wR(F²) = 0.074
S = 1.06
2409 reflections
83 parameters
H-atom parameters constrained
Δρ_max = 0.65 e Å⁻³
Δρ_min = −0.67 e Å⁻³

Table 1
Selected bond lengths (Å)

As1—O1	1.6477 (16)
As1—O2	1.6531 (16)
As1—O3	1.6974 (16)
As1—O4	1.7082 (17)

Table 2
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O4—H2⋯O1ⁱ	0.84	1.76	2.599 (3)	174
O3—H1⋯O2ⁱⁱ	0.86	1.70	2.548 (2)	169
N1—H4⋯O2	0.90	1.79	2.689 (2)	175
N1—H3⋯O1ⁱⁱⁱ	0.90	1.80	2.685 (2)	168
Symmetry codes: (i) -x+1, -y+1, -z+1; (ii) $[-x+1, y+{\script{1\over 2}}, -z+{\script{3\over 2}}]$ ; (iii) -x, -y+1, -z+1.

The C3 methyl group is disordered over two positions in the molecule. Crystal symmetry dictates equal occupancy for both components. The O-bound H atoms were found in a difference map and refined as riding in their as-found relative positions, with U_iso(H) = 1.2U_eq(O) (see Table 2 for distances). The C- and N-bonded H atoms were placed in idealized positions (C—H = 0.96–0.97 Å and N—H = 0.90 Å) and refined as riding, with U_iso(H) = 1.2U_eq(C,N) or 1.5U_eq(methyl C). The methyl group was allowed to rotate, but not to tip, to best fit the electron density.

Data collection: SMART (Bruker, 1999); cell refinement: SAINT (Bruker, 1999); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 (Farrugia, 1997 ) and ATOMS (Shape Software, 2004 ); software used to prepare material for publication: SHELXL97.

Supporting information

Crystal structure: contains datablocks I, global. DOI: https://doi.org/10.1107/S1600536807008392/tk2140sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536807008392/tk2140Isup2.hkl

Computing details top

Data collection: SMART (Bruker, 1999); cell refinement: SAINT (Bruker, 1999); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 (Farrugia, 1997) and ATOMS (Shape Software, 2004); software used to prepare material for publication: SHELXL97.

2-Methylpiperazinium bis(dihydrogenarsenate) top

Crystal data top

C₅H₁₄N₂²⁺·2AsH₂O₄⁻	F(000) = 384
M_r = 384.06	D_x = 1.906 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 3599 reflections
a = 6.7537 (3) Å	θ = 3.0–32.5°
b = 8.1753 (4) Å	µ = 5.02 mm⁻¹
c = 12.7105 (5) Å	T = 293 K
β = 107.501 (2)°	Blade, colourless
V = 669.31 (5) Å³	0.37 × 0.12 × 0.03 mm
Z = 2

Data collection top

Bruker SMART1000 CCD diffractometer	2409 independent reflections
Radiation source: fine-focus sealed tube	1929 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.026
ω scans	θ_max = 32.5°, θ_min = 3.0°
Absorption correction: multi-scan (SADABS; Bruker, 1999)	h = −10→8
T_min = 0.258, T_max = 0.864	k = −12→10
6913 measured reflections	l = −19→19

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)] = 0.029	Hydrogen site location: difmap and geom
wR(F²) = 0.074	H-atom parameters constrained
S = 1.06	w = 1/[σ²(F_o²) + (0.042P)²] where P = (F_o² + 2F_c²)/3
2409 reflections	(Δ/σ)_max < 0.001
83 parameters	Δρ_max = 0.65 e Å⁻³
0 restraints	Δρ_min = −0.67 e Å⁻³

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)
As1	0.42568 (3)	0.44828 (2)	0.649888 (15)	0.02836 (7)
O1	0.2951 (3)	0.5701 (2)	0.54973 (14)	0.0430 (4)
O2	0.3233 (3)	0.2636 (2)	0.64397 (13)	0.0431 (4)
O3	0.4450 (3)	0.5192 (3)	0.77811 (14)	0.0495 (5)
H1	0.5209	0.6055	0.7961	0.059*
O4	0.6781 (3)	0.4345 (2)	0.65004 (14)	0.0484 (5)
H2	0.6918	0.4387	0.5862	0.058*
N1	−0.0381 (3)	0.1715 (2)	0.49849 (15)	0.0382 (4)
H3	−0.1195	0.2590	0.4734	0.046*
H4	0.0794	0.2070	0.5480	0.046*
C1	−0.1470 (4)	0.0578 (3)	0.5536 (2)	0.0432 (5)
H1A	−0.2786	0.0251	0.5020	0.052*
H1B	−0.1750	0.1127	0.6153	0.052*
C2	0.0139 (4)	0.0927 (3)	0.40532 (19)	0.0411 (5)
H2A	−0.1125	0.0613	0.3489	0.049*
H2B	0.0893	0.1687	0.3730	0.049*	0.50
C3	0.1037 (8)	0.2083 (7)	0.3563 (4)	0.0443 (11)	0.50
H3A	0.0336	0.3109	0.3543	0.067*	0.50
H3B	0.0931	0.1746	0.2825	0.067*	0.50
H3C	0.2473	0.2204	0.3979	0.067*	0.50

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
As1	0.03332 (12)	0.02582 (11)	0.02342 (10)	0.00174 (8)	0.00472 (7)	−0.00104 (7)
O1	0.0517 (10)	0.0406 (9)	0.0385 (8)	0.0223 (7)	0.0163 (7)	0.0131 (7)
O2	0.0483 (9)	0.0289 (8)	0.0387 (8)	−0.0048 (7)	−0.0073 (7)	0.0019 (6)
O3	0.0695 (12)	0.0511 (11)	0.0351 (8)	−0.0228 (9)	0.0264 (8)	−0.0164 (8)
O4	0.0333 (8)	0.0767 (14)	0.0329 (8)	0.0071 (8)	0.0064 (6)	0.0050 (8)
N1	0.0386 (9)	0.0284 (8)	0.0367 (9)	0.0113 (7)	−0.0051 (7)	−0.0046 (8)
C1	0.0461 (13)	0.0352 (12)	0.0418 (12)	0.0095 (9)	0.0034 (10)	−0.0039 (10)
C2	0.0478 (13)	0.0351 (10)	0.0324 (10)	0.0093 (9)	−0.0002 (9)	−0.0013 (9)
C3	0.054 (3)	0.041 (3)	0.047 (3)	−0.001 (2)	0.027 (2)	0.006 (2)

Geometric parameters (Å, º) top

As1—O1	1.6477 (16)	C1—C2ⁱ	1.520 (3)
As1—O2	1.6531 (16)	C1—H1A	0.9700
As1—O3	1.6974 (16)	C1—H1B	0.9700
As1—O4	1.7082 (17)	C2—C3	1.370 (5)
O3—H1	0.8619	C2—C1ⁱ	1.520 (3)
O4—H2	0.8442	C2—H2A	0.9700
N1—C2	1.480 (3)	C2—H2B	0.9700
N1—C1	1.485 (3)	C3—H3A	0.9600
N1—H3	0.9000	C3—H3B	0.9600
N1—H4	0.9000	C3—H3C	0.9600

O1—As1—O2	113.42 (9)	H1A—C1—H1B	108.2
O1—As1—O3	113.84 (10)	C3—C2—N1	107.9 (3)
O2—As1—O3	105.42 (9)	C3—C2—C1ⁱ	114.7 (3)
O1—As1—O4	110.05 (9)	N1—C2—C1ⁱ	109.62 (19)
O2—As1—O4	110.11 (9)	C3—C2—H2A	104.9
O3—As1—O4	103.47 (9)	N1—C2—H2A	109.9
As1—O3—H1	113.7	C1ⁱ—C2—H2A	109.7
As1—O4—H2	113.2	N1—C2—H2B	110.0
C2—N1—C1	112.03 (18)	C1ⁱ—C2—H2B	109.4
C2—N1—H3	109.2	H2A—C2—H2B	108.2
C1—N1—H3	109.2	C2—C3—H3A	109.5
C2—N1—H4	109.2	H2B—C3—H3A	120.5
C1—N1—H4	109.2	C2—C3—H3B	109.5
H3—N1—H4	107.9	H2B—C3—H3B	108.4
N1—C1—C2ⁱ	110.1 (2)	H3A—C3—H3B	109.5
N1—C1—H1A	109.6	C2—C3—H3C	109.5
C2ⁱ—C1—H1A	109.6	H2B—C3—H3C	98.9
N1—C1—H1B	109.6	H3A—C3—H3C	109.5
C2ⁱ—C1—H1B	109.6	H3B—C3—H3C	109.5

C2—N1—C1—C2ⁱ	57.8 (3)	C1—N1—C2—C1ⁱ	−57.5 (3)
C1—N1—C2—C3	177.0 (3)

Symmetry code: (i) −x, −y, −z+1.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O4—H2···O1ⁱⁱ	0.84	1.76	2.599 (3)	174
O3—H1···O2ⁱⁱⁱ	0.86	1.70	2.548 (2)	169
N1—H4···O2	0.90	1.79	2.689 (2)	175
N1—H3···O1^iv	0.90	1.80	2.685 (2)	168

Symmetry codes: (ii) −x+1, −y+1, −z+1; (iii) −x+1, y+1/2, −z+3/2; (iv) −x, −y+1, −z+1.

Acknowledgements

HSW thanks the Carnegie Trust for the Universities of Scotland for an undergraduate vacation studentship.

References

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