Crystal structure of di­methyl­ammonium hydrogen oxalate hemi(oxalic acid)

The title salt consists of a di­methyl­ammonium cation (Me₂NH₂ ⁺), an hydrogenoxalate anion (HC₂O₄ ⁻), and half a mol­ecule of oxalic acid (H₂C₂O₄) situated about an inversion center. They are linked together through inter­molecular hydrogen bonds, forming a two-dimensional bilayer-like self-assembly.

Abstract

Single crystals of the title salt, Me₂NH₂ ⁺·HC₂O₄ ⁻·0.5H₂C₂O₄, were isolated as a side product from the reaction involving Me₂NH, H₂C₂O₄ and Sn(n-Bu)₃Cl in a 1:2 ratio in methanol or by the reaction of the (Me₂NH₂)₂C₂O₄ salt and Sn(CH₃)₃Cl in a 2:1 ratio in ethanol. The asymmetric unit comprises a di­methyl­ammonium cation (Me₂NH₂ ⁺), an hydrogenoxalate anion (HC₂O₄ ⁻), and half a mol­ecule of oxalic acid (H₂C₂O₄) situated about an inversion center. From a supra­molecular point of view, the three components inter­act together via hydrogen bonding. The Me₂NH₂ ⁺ cations and the HC₂O₄ ⁻ anions are in close proximity through bifurcated N—H⋯(O,O) hydrogen bonds, while the HC₂O₄ ⁻ anions are organized into infinite chains via O—H⋯O hydrogen bonds, propagating along the a-axis direction. In addition, the oxalic acid (H₂C₂O₄) mol­ecules play the role of connectors between these chains. Both the carbonyl and hydroxyl groups of each diacid are involved in four inter­molecular inter­actions with two Me₂NH₂ ⁺ and two HC₂O₄ ⁻ ions of four distinct polymeric chains, via two N—H⋯O and two O—H⋯O hydrogen bonds, respectively. The resulting mol­ecular assembly can be viewed as a two-dimensional bilayer-like arrangement lying parallel to (010), and reinforced by a C—H⋯O hydrogen bond.

Chemical context  

Within the scope of our research on the crystal structure determination of new organotin compounds containing dialkyammonium, we recently reported the structures of bis­(di­methyl­ammonium) tetra­chlorido­dimethyl­stannate(IV) [Diop et al., 2011 ▸] and di­methyl­ammonium di­chlorido­tri­phenyl­stannate(IV) [Sow et al., 2012 ▸]. Continuing our quest in this field, we report herein on the crystal structure of the title salt, Me₂NH₂ ⁺·HC₂O₄ ⁻·0.5H₂C₂O₄, isolated from two distinct reaction pathways, viz. mixing Me₂NH, H₂C₂O₄ and SnBu₃Cl in methanol or the reaction of the (Me₂NH₂)₂C₂O₄ salt and Sn(CH₃)₃Cl in ethanol.

The title salt constitutes a new example of di­alkyl­ammonium hydrogenoxalates and thus supplements the number of crystal structures resolved to date for this type of salt (Birnbaum, 1972 ▸; Thomas & Pramatus, 1975 ▸; Thomas, 1977 ▸; Gündisch et al., 2001 ▸; Warden et al., 2005 ▸). In addition, and because of their capacity to easily develop hydrogen-bonding networks, carb­oxy­lic acids and their deriv­atives are of great inter­est in the field of crystal engineering, leading to a large diversity of supra­molecular topologies (Ivasenko & Perepichka, 2011 ▸).

Structural comments  

In the asymmetric unit of the title salt there are three components: one di­methyl­ammonium cation (Me₂NH₂ ⁺), one hydrogenoxalate anion (HC₂O₄ ⁻), and half a mol­ecule of oxalic acid (H₂C₂O₄) which possess inversion symmetry (Fig. 1 ▸). All three entities are linked by inter­molecular inter­actions (Table 1 ▸ and Fig. 2 ▸). The Me₂NH₂ ⁺ cation is in close proximity with the HC₂O₄ ⁻ anion through bifurcated N—H⋯(O,O) hydrogen bonds [N1—H1A⋯O1 = 2.854 (1) Å and N1—H1A⋯O4 = 2.964 (1) Å]. The lengths of the N–C bonds [N1—C4 = 1.4822 (12) and N1—C5 = 1.4842 (12) Å] are nearly identical of those reported previously for Me₂NH₂ ⁺·HC₂O₄ ⁻ (Thomas, 1977 ▸). The Me₂NH₂ ⁺ cation is also involved in hydrogen bonding with one of the two carbonyl groups of the oxalic acid mol­ecule [N1—H1B⋯O6 = 2.846 (1) Å]. The HC₂O₄ ⁻ hydrogenoxalate anions form a one-dimensional chain along the a-axis direction via the formation of O—H⋯O hydrogen bonds [O3—H3⋯O1 = 2.564 (1) Å]. Furthermore, the HC₂O₄ ⁻ anion is also involved in hydrogen bonding with one of the two hydroxyl groups of the oxalic acid mol­ecule [O5—H5⋯O2 = 2.565 (1) Å].

Figure 1.

A view of the mol­ecular structure of the title salt, with the atom labelling. Displacement ellipsoids are drawn at the 30% probability level.

Table 1. Hydrogen-bond geometry (, ).

DHA	DH	HA	D A	DHA
O3H3O1i	0.84	1.73	2.564(1)	174
O5H5O2	0.84	1.73	2.565(1)	170
N1H1AO1ii	0.91	2.08	2.854(1)	143
N1H1AO4ii	0.91	2.23	2.964(1)	137
N1H1BO6	0.91	2.05	2.846(1)	146
C5H5CO4iii	0.98	2.41	3.346(1)	159

Symmetry codes: (i) ; (ii) ; (iii) .

Figure 2.

Crystal packing of the title salt, viewed along the a axis, showing the two-dimensional bilayer-like arrangement formed through N—H⋯O and O—H⋯O hydrogen bonds (dashed lines; details are given in Table 1 ▸). H atoms not involved in hydrogen bonding have been omitted for clarity.

Supra­molecular features  

From a supra­molecular point of view, the combination of these inter­molecular inter­actions leads to the formation of a mol­ecular assembly which can be described as a two-dimensional bilayer-like arrangement, parallel to (010), consisting of anti­parallel infinite chains of Me₂NH₂ ⁺·HC₂O₄ ⁻ (Table 1 ▸ and Fig. 3 ▸), with an inter-chain distance of ca 3.0 Å. The oxalic acid mol­ecules are organized in a parallel offset fashion, and act as hydrogen-bond connectors between the chains, involving both the carbonyl and hydroxyl groups (Table 1 ▸ and Figs. 2 ▸ and 3 ▸).

Figure 3.

Crystal packing of the title salt viewed along the b axis. The hydrogen bonds are shown as dashed lines (see Table 1 ▸ for details) and H atoms not involved in hydrogen bonding have been omitted for clarity.

Database survey  

The crystal structure of Me₂NH₂ ⁺·HC₂O₄ ⁻, first reported by Thomas & Pramatus (1975 ▸) and then completed in 1977 (Thomas, 1977 ▸), shows a supra­molecular structure qualified as a puckered layer. In particular, the HC₂O₄ ⁻ ions are linked via O—H⋯O hydrogen bonds [2.533 (1) Å], leading to an infinite chain along [100]. In the title salt, the HC₂O₄ ⁻ ions inter­act in the same manner but through slightly longer O—H⋯O hydrogen bonds [2.564 (1) Å]. In addition, the oxalic acid mol­ecules that co-crystallize with Me₂NH₂ ⁺·HC₂O₄ ⁻ act both as donors and acceptors of hydrogen bonds through N—H⋯O and O—H⋯O bonds with the Me₂NH₂ ⁺ cation and HC₂O₄ ⁻ anion, respectively. Consequently, the degree of supra­molecularity is increased here, resulting in a two-dimensional architecture parallel to (010), which is reinforced by a C—H⋯O hydrogen bond (Table 1 ▸ and Figs. 2 ▸ and 3 ▸).

Synthesis and crystallization  

Crystals of the title compound were obtained by mixing in 20 ml methanol (98% purity) Me₂NH (0.30 g, 6.67 mmol), H₂C₂O₄ (0.60 g, 6.67 mmol) and Sn(n-Bu)₃Cl (4.39 g, 13.33 mmol). Another experimental method is the reaction between the (Me₂NH₂)₂C₂O₄ salt (0.50 g, 2.77 mmol), previously synthesized from oxalic acid and di­methyl­amine, and Sn(CH₃)₃Cl (0.28 g, 1.39 mmol) in 15 ml of ethanol (98% purity). In both cases, the reaction mixture was stirred for ca 2 h at room temperature. Colourless crystals were obtained after one week by slow evaporation of the solvent.

Refinement  

Crystal data, data collection and structure refinement details are summarized in Table 2 ▸. All the H atoms were placed in calculated positions and refined as riding: O—H = 0.84 Å, N—H = 0.91 Å, and C—H = 0.98 Å with U _iso(H) = 1.5U _eq(C,O) and 1.2U _eq(N).

Table 2. Experimental details.

Crystal data
Chemical formula	C2H8N+C2HO4 0.5C2H2O4
M r	180.14
Crystal system, space group	Triclinic, P
Temperature (K)	100
a, b, c ()	5.6519(3), 7.5809(4), 10.3100(6)
, , ()	75.467(2), 88.120(2), 69.487(2)
V (3)	399.76(4)
Z	2
Radiation type	Mo K
(mm1)	0.14
Crystal size (mm)	0.5 0.3 0.1
Data collection
Diffractometer	Bruker D8 Venture triumph Mo
Absorption correction	Multi-scan (SADABS; Bruker, 2014 ▸)
T min, T max	0.693, 0.746
No. of measured, independent and observed [I 2(I)] reflections	10413, 1840, 1655
R int	0.023
(sin /)max (1)	0.651
Refinement
R[F 2 > 2(F 2)], wR(F 2), S	0.028, 0.075, 1.07
No. of reflections	1840
No. of parameters	113
H-atom treatment	H-atom parameters not refined
max, min (e 3)	0.38, 0.26

Computer programs: APEX2 and SAINT (Bruker, 2014 ▸), SUPERFLIP (Palatinus Chapuis, 2007 ▸), SHELXL2014 (Sheldrick, 2015 ▸), OLEX2 (Dolomanov et al., 2009 ▸) and Mercury (Macrae et al., 2008 ▸.

Supplementary Material

CCDC reference: 1055825

Additional supporting information: crystallographic information; 3D view; checkCIF report

supplementary crystallographic information

Crystal data

C2H8N+·C2HO4−·0.5C2H2O4	Z = 2
Mr = 180.14	F(000) = 190.1598
Triclinic, P1	Dx = 1.497 Mg m−3
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 5.6519 (3) Å	Cell parameters from 7049 reflections
b = 7.5809 (4) Å	θ = 3.0–27.6°
c = 10.3100 (6) Å	µ = 0.14 mm−1
α = 75.467 (2)°	T = 100 K
β = 88.120 (2)°	Prism, colourless
γ = 69.487 (2)°	0.5 × 0.3 × 0.1 mm
V = 399.76 (4) Å3

Data collection

Bruker D8 Venture triumph Mo diffractometer	1840 independent reflections
Radiation source: X-ray tube, Siemens KFF Mo 2K-90C	1655 reflections with I≥ 2σ(I)
TRIUMPH curved crystal monochromator	Rint = 0.023
φ and ω scans	θmax = 27.6°, θmin = 3.0°
Absorption correction: multi-scan (SADABS; Bruker, 2014)	h = −7→7
Tmin = 0.693, Tmax = 0.746	k = −9→9
10413 measured reflections	l = −13→13

Refinement

Refinement on F2	0 restraints
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.028	H-atom parameters not refined
wR(F2) = 0.075	w = 1/[σ2(Fo2) + (0.0375P)2 + 0.1325P] where P = (Fo2 + 2Fc2)/3
S = 1.07	(Δ/σ)max = 0.001
1840 reflections	Δρmax = 0.38 e Å−3
113 parameters	Δρmin = −0.26 e Å−3

Special details

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
O1	0.75407 (12)	0.32103 (10)	0.47166 (7)	0.01407 (16)
O2	0.57685 (12)	0.40754 (10)	0.26360 (7)	0.01329 (16)
O3	0.14369 (12)	0.38767 (11)	0.36954 (7)	0.01625 (17)
H3	0.0215	0.3632	0.4083	0.024*
O4	0.36051 (14)	0.20987 (11)	0.56626 (7)	0.02010 (17)
O5	0.29036 (13)	0.37192 (10)	0.09144 (7)	0.01471 (16)
H5	0.3683	0.3944	0.1497	0.022*
O6	0.01961 (13)	0.67729 (10)	0.07499 (7)	0.01568 (16)
C1	0.57857 (16)	0.34999 (13)	0.38821 (9)	0.01061 (18)
C2	0.34558 (17)	0.30728 (13)	0.45205 (9)	0.01216 (19)
C3	0.08336 (17)	0.52128 (13)	0.04793 (9)	0.01171 (19)
N1	0.22327 (15)	0.83866 (11)	0.24521 (8)	0.01223 (17)
H1A	0.3034	0.7852	0.3284	0.015*
H1B	0.1697	0.7490	0.2236	0.015*
C4	0.40571 (19)	0.88277 (15)	0.14735 (10)	0.0182 (2)
H4A	0.3224	0.9359	0.0569	0.027*
H4B	0.5500	0.7630	0.1500	0.027*
H4C	0.4653	0.9785	0.1705	0.027*
C5	−0.00007 (19)	1.01362 (14)	0.24892 (11)	0.0177 (2)
H5A	−0.0886	1.0711	0.1598	0.027*
H5B	0.0557	1.1091	0.2751	0.027*
H5C	−0.1149	0.9761	0.3143	0.027*

Atomic displacement parameters (Ų)

	U11	U22	U33	U12	U13	U23
O1	0.0100 (3)	0.0212 (4)	0.0119 (3)	−0.0072 (3)	−0.0008 (2)	−0.0031 (3)
O2	0.0113 (3)	0.0178 (3)	0.0107 (3)	−0.0060 (3)	−0.0004 (2)	−0.0024 (3)
O3	0.0089 (3)	0.0274 (4)	0.0131 (3)	−0.0087 (3)	0.0002 (3)	−0.0030 (3)
O4	0.0162 (4)	0.0286 (4)	0.0148 (3)	−0.0123 (3)	−0.0008 (3)	0.0022 (3)
O5	0.0134 (3)	0.0149 (3)	0.0150 (3)	−0.0021 (3)	−0.0044 (3)	−0.0059 (3)
O6	0.0178 (3)	0.0130 (3)	0.0166 (3)	−0.0046 (3)	−0.0040 (3)	−0.0051 (3)
C1	0.0087 (4)	0.0105 (4)	0.0127 (4)	−0.0028 (3)	0.0003 (3)	−0.0039 (3)
C2	0.0103 (4)	0.0154 (4)	0.0126 (4)	−0.0057 (3)	0.0004 (3)	−0.0050 (3)
C3	0.0127 (4)	0.0138 (4)	0.0091 (4)	−0.0059 (3)	−0.0003 (3)	−0.0018 (3)
N1	0.0145 (4)	0.0118 (4)	0.0107 (4)	−0.0050 (3)	−0.0005 (3)	−0.0028 (3)
C4	0.0166 (5)	0.0202 (5)	0.0186 (5)	−0.0074 (4)	0.0050 (4)	−0.0055 (4)
C5	0.0152 (5)	0.0148 (4)	0.0211 (5)	−0.0037 (4)	0.0033 (4)	−0.0034 (4)

Geometric parameters (Å, º)

O1—C1	1.2573 (11)	N1—H1A	0.9100
O2—C1	1.2480 (11)	N1—H1B	0.9100
O3—H3	0.8400	N1—C4	1.4822 (12)
O3—C2	1.3089 (11)	N1—C5	1.4842 (12)
O4—C2	1.2105 (12)	C4—H4A	0.9800
O5—H5	0.8400	C4—H4B	0.9800
O5—C3	1.3051 (11)	C4—H4C	0.9800
O6—C3	1.2111 (12)	C5—H5A	0.9800
C1—C2	1.5515 (13)	C5—H5B	0.9800
C3—C3i	1.5501 (17)	C5—H5C	0.9800
C2—O3—H3	109.5	C5—N1—H1A	109.0
C3—O5—H5	109.5	C5—N1—H1B	109.0
O1—C1—C2	114.27 (8)	N1—C4—H4A	109.5
O2—C1—O1	126.60 (8)	N1—C4—H4B	109.5
O2—C1—C2	119.13 (8)	N1—C4—H4C	109.5
O3—C2—C1	112.45 (8)	H4A—C4—H4B	109.5
O4—C2—O3	126.54 (9)	H4A—C4—H4C	109.5
O4—C2—C1	121.01 (8)	H4B—C4—H4C	109.5
O5—C3—C3i	111.64 (10)	N1—C5—H5A	109.5
O6—C3—O5	126.87 (8)	N1—C5—H5B	109.5
O6—C3—C3i	121.48 (10)	N1—C5—H5C	109.5
H1A—N1—H1B	107.8	H5A—C5—H5B	109.5
C4—N1—H1A	109.0	H5A—C5—H5C	109.5
C4—N1—H1B	109.0	H5B—C5—H5C	109.5
C4—N1—C5	112.87 (8)
O1—C1—C2—O3	162.31 (8)	O2—C1—C2—O3	−17.79 (12)
O1—C1—C2—O4	−17.45 (13)	O2—C1—C2—O4	162.45 (9)

Symmetry code: (i) −x, −y+1, −z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O3—H3···O1ii	0.84	1.73	2.564 (1)	174
O5—H5···O2	0.84	1.73	2.565 (1)	170
N1—H1A···O1iii	0.91	2.08	2.854 (1)	143
N1—H1A···O4iii	0.91	2.23	2.964 (1)	137
N1—H1B···O6	0.91	2.05	2.846 (1)	146
C5—H5C···O4iv	0.98	2.41	3.346 (1)	159

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