Benzyl­ammonium hydrogen oxalate hemihydrate

α-Amino­toluene (benzyl­amine) reacts with ethanedioic acid (oxalic acid) to form C₆H₅CH₂NH₃⁺·C₂HO₄⁻·0.5H₂O. The mono­hydrogeno­xalate ions form hydrogen-bonded chains [2.558 (1) Å], linked into pairs by hydrogen bonds [2.758 (1) Å] to a water mol­ecule lying on a crystallographic twofold axis. Three hydrogen bonds [2.833 (1)–2.896 (1) Å] from each benzyl­ammonium ion connect these chains into layers.

Key indicators

• Single-crystal X-ray study
• T = 120 K
• Mean [sigma](C-C) = 0.002 Å
• R factor = 0.037
• wR factor = 0.095
• Data-to-parameter ratio = 15.0

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level C:



PLAT_369  Alert C Long   C(sp2)-C(sp2) Bond  C9     -   C10      =       1.55 Ang.


 0 Alert Level A = Potentially serious problem

 0 Alert Level B = Potential problem

 1 Alert Level C = Please check

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S1. Comment

On paper, the reaction of a simple amine with a polycarboxylic acid should yield a series of products in which the anion ranges from the fully deprotonated A^n- through the various possibilities of HA^n-1, H₂A^n-2 etc. In practice this happens rarely. Often only one product is isolated, regardless of the initial ratio of the components. Since crystallization from these mixtures is slow, often requiring days at room temperature, the compound obtained is likely to be the most thermodynamically stable, the deepest well in the multi-dimensional composition/energy surface. A major factor in this stability must be the ability to form an optimal extended hydrogen-bonded array. Water molecules and —COOH groups play a major part in constructing these assemblies. The significance of these hydrogen-bonded networks in molecular biology has been discussed by Jeffrey & Saenger (1994). Examples from this laboratory include di- tri-and tetra-carboxylates, in which the groups linking the acid functions may be rigid (Barnes et al., 1991, 1997, 2003) or rotationally unrestricted (Barnes et al., 1996, 1998a, 1998b, 2000).

Oxalic acid reacts with diethylenetriamine to give crystals of the fully deprotonated C₂O₄²⁻ salt as the tetrahydrate. This has been found as two polymorphs (Román et al. 1997; Barnes & Weakley,1998). More often, amine salts with oxalic acid contain the monohydrogenoxalate ion, seen, for example, in the series of [NH₃(CH₂)_nNH₃]²⁺ salts (Vijayalakshmi & Srinivasan, 1983; Babu et al., 1998; Barnes, Longhurst & Weakley, 1998). This anion also appears in the benzylammonium salt, (I), reported here. The components of (I) are shown in Fig. 1. The monohydrogenoxalate ion is not quite planar, there is a twist of 13.55 (4)° between the carboxylate groups.

The use of the mono-functional benzylamine in (I) restricts the possibilities for hydrogen bonding by comparison with those in the di- or triamine compounds. As before (Barnes & Weakley, 1998), the monohydrogenoxalate ions form linear chains. In (I), these lie parallel to the b axis [O14—H14···O12(x, 1 + y, z) 2.558 (1) Å] (Fig. 2). These chains are crosslinked by the water molecule O15 which lies on the special position (1/2, y, 1/4), [O15—H15···O11 2.758 (1) Å]. Fig. 3 shows how layers parallel to the bc plane are completed by hydrogen bonds from N8 to the water molecule [N8—H82···O15(x, y − 1, z) 2.838 (1) Å] and to two monohydrogenoxalate ions [N8—H81···O11 2.896 (1) and N8—H83···O12(1 − x, 1 − y, −z) 2.833 (1) Å]. With the position of N8 determined by the hydrogen bonding, the torsion angle C2—C1—C7—N8 [66.48 (14)°] allows for efficient packing of the phenyl rings between the layers. Although there is good overlap between adjacent rings from adjacent layers, the interplanar distance of over 4.2 Å indicates that there is no π interaction between them.

S2. Experimental

Crystals were grown by slow evaporation of an aqueous mixture of benzylamine (0.01 mol) and oxalic acid (0.01 mol).

S3. Refinement

H atoms attached to C atoms were placed in calculated positions and allowed to ride during the refinement, with U_iso constrained to be 1.3U_eq of the parent C atom. H atoms attached to O or N atoms were located on a difference synthesis. The positional and isotropic displacement parameters of these H atoms were allowed to refine.

Computing details

Data collection: DENZO (Otwinowski and Minor, 1997) COLLECT (Hooft, 1998); cell refinement: DENZO and COLLECT; data reduction: DENZO and COLLECT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 1999).

Figures

	Fig. 1. The components of (I), with displacement ellipsoids drawn at the 50% probability level.
	Fig. 2. Monohydrogenoxalate chains are linked into pairs by hydrogen bonding to the water molecule. The b axis is horisontal.
	Fig. 3. View down b, showing the inter-linking of the monohydrogenoxalate chains by hydrogen bonds to the benzylammonium ions. The a axis is horizontal.

Benzylammonium hydrogen oxalate hemihydrate

Crystal data

C7H10N^+·C2HO4^−·0.5H2O	F(000) = 872
Mr = 206.20	Dx = 1.368 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
a = 21.7449 (7) Å	Cell parameters from 7634 reflections
b = 5.6370 (2) Å	θ = 2.9–27.5°
c = 16.4499 (5) Å	µ = 0.11 mm^−1
β = 96.830 (2)°	T = 120 K
V = 2002.05 (11) Å^3	Block, colourless
Z = 8	0.25 × 0.20 × 0.07 mm

Data collection

Enraf Nonius KappaCCD area-detector diffractometer	1964 reflections with I > 2σ(I)
Radiation source: Enraf Nonius FR591 rotating anode	Rint = 0.050
Graphite monochromator	θmax = 27.5°, θmin = 3.3°
Detector resolution: 9.091 pixels mm^-1	h = −28→28
ϕ and ω scans to fill Ewald sphere	k = −7→7
10464 measured reflections	l = −21→20
2284 independent 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)] = 0.037	Hydrogen site location: mixed
wR(F^2) = 0.095	H atoms treated by a mixture of independent and constrained refinement
S = 1.03	w = 1/[σ^2(Fo^2) + (0.0425P)^2 + 0.7396P] where P = (Fo^2 + 2Fc^2)/3
2284 reflections	(Δ/σ)max = 0.032
152 parameters	Δρmax = 0.27 e Å^−3
0 restraints	Δρmin = −0.18 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.

Refinement. H atoms attached to C atoms were placed in calculated positions and allowed to ride during the refinement. Isotropic displacement parameters were constrained to be 1.3U_eq of the parent C atom. H atoms attached to O or N atoms were located on a difference synthesis. The positional and isotropic displacement parameters of these H atoms were allowed to refine.

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 (Ų)

	x	y	z	Uiso*/Ueq
C1	0.33161 (5)	0.3924 (2)	0.15648 (7)	0.0322 (3)
C2	0.32992 (6)	0.1873 (2)	0.20291 (8)	0.0366 (3)
H2	0.3642	0.1478	0.2419	0.048*
C3	0.27849 (6)	0.0396 (3)	0.19281 (9)	0.0445 (3)
H3	0.2779	−0.1015	0.2243	0.058*
C4	0.22798 (6)	0.0977 (3)	0.13699 (9)	0.0484 (4)
H4	0.1928	−0.0036	0.1301	0.063*
C5	0.22881 (6)	0.3028 (3)	0.09144 (9)	0.0492 (4)
H5	0.1940	0.3436	0.0536	0.064*
C6	0.28047 (6)	0.4499 (3)	0.10082 (8)	0.0404 (3)
H6	0.2809	0.5906	0.0691	0.053*
C7	0.38771 (6)	0.5506 (2)	0.16610 (7)	0.0344 (3)
H7A	0.3787	0.6975	0.1339	0.045*
H7B	0.3975	0.5956	0.2244	0.045*
N8	0.44239 (5)	0.42839 (19)	0.13769 (6)	0.0312 (2)
H81	0.4763 (7)	0.530 (3)	0.1401 (9)	0.044 (4)*
H82	0.4534 (7)	0.300 (3)	0.1719 (9)	0.041 (4)*
H83	0.4344 (7)	0.385 (3)	0.0840 (10)	0.040 (4)*
C9	0.56256 (5)	0.77299 (19)	0.08150 (6)	0.0261 (2)
C10	0.56944 (5)	1.02345 (19)	0.04495 (7)	0.0269 (2)
O11	0.54592 (4)	0.75476 (14)	0.15112 (4)	0.0311 (2)
O12	0.57374 (4)	0.60458 (14)	0.03539 (5)	0.0332 (2)
O13	0.57319 (4)	1.05086 (15)	−0.02692 (5)	0.0374 (2)
O14	0.56921 (4)	1.19256 (14)	0.09960 (5)	0.0339 (2)
H14	0.5718 (8)	1.343 (4)	0.0761 (11)	0.066 (5)*
O15	0.5000	1.0903 (2)	0.2500	0.0336 (3)
H15	0.5163 (8)	0.994 (3)	0.2160 (10)	0.058 (5)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0326 (6)	0.0334 (6)	0.0315 (6)	0.0008 (5)	0.0080 (5)	−0.0044 (5)
C2	0.0335 (6)	0.0367 (7)	0.0404 (6)	0.0019 (5)	0.0083 (5)	0.0006 (5)
C3	0.0433 (7)	0.0378 (7)	0.0553 (8)	−0.0039 (6)	0.0182 (6)	−0.0019 (6)
C4	0.0350 (7)	0.0541 (9)	0.0578 (8)	−0.0097 (6)	0.0125 (6)	−0.0139 (7)
C5	0.0338 (7)	0.0684 (10)	0.0445 (7)	0.0010 (6)	0.0009 (5)	−0.0082 (7)
C6	0.0390 (7)	0.0460 (7)	0.0361 (6)	0.0031 (5)	0.0043 (5)	0.0012 (6)
C7	0.0364 (6)	0.0317 (6)	0.0359 (6)	−0.0018 (5)	0.0079 (5)	−0.0032 (5)
N8	0.0316 (5)	0.0328 (5)	0.0296 (5)	−0.0039 (4)	0.0049 (4)	0.0001 (4)
C9	0.0269 (5)	0.0231 (5)	0.0282 (5)	−0.0010 (4)	0.0021 (4)	0.0020 (4)
C10	0.0264 (5)	0.0241 (5)	0.0300 (5)	−0.0010 (4)	0.0032 (4)	0.0003 (4)
O11	0.0390 (4)	0.0264 (4)	0.0287 (4)	−0.0010 (3)	0.0073 (3)	0.0018 (3)
O12	0.0458 (5)	0.0228 (4)	0.0318 (4)	−0.0002 (3)	0.0078 (3)	−0.0008 (3)
O13	0.0527 (5)	0.0308 (4)	0.0299 (4)	−0.0022 (4)	0.0099 (4)	0.0027 (3)
O14	0.0489 (5)	0.0216 (4)	0.0319 (4)	−0.0018 (3)	0.0075 (4)	0.0002 (3)
O15	0.0402 (7)	0.0301 (6)	0.0321 (6)	0.000	0.0109 (5)	0.000

Geometric parameters (Å, º)

C1—C2	1.3886 (17)	C7—H7A	0.9900
C1—C6	1.3921 (18)	C7—H7B	0.9900
C1—C7	1.5040 (17)	N8—H81	0.933 (17)
C2—C3	1.3882 (19)	N8—H82	0.930 (16)
C2—H2	0.9500	N8—H83	0.912 (15)
C3—C4	1.384 (2)	C9—O11	1.2457 (13)
C3—H3	0.9500	C9—O12	1.2567 (13)
C4—C5	1.379 (2)	C9—C10	1.5487 (15)
C4—H4	0.9500	C10—O13	1.2046 (13)
C5—C6	1.390 (2)	C10—O14	1.3109 (13)
C5—H5	0.9500	O14—H14	0.94 (2)
C6—H6	0.9500	O15—H15	0.882 (17)
C7—N8	1.4961 (15)
C2—C1—C6	118.96 (11)	N8—C7—H7A	109.4
C2—C1—C7	120.66 (11)	C1—C7—H7A	109.4
C6—C1—C7	120.37 (11)	N8—C7—H7B	109.4
C3—C2—C1	120.48 (12)	C1—C7—H7B	109.4
C3—C2—H2	119.8	H7A—C7—H7B	108.0
C1—C2—H2	119.8	C7—N8—H81	110.9 (9)
C4—C3—C2	120.13 (13)	C7—N8—H82	109.0 (9)
C4—C3—H3	119.9	H81—N8—H82	108.1 (13)
C2—C3—H3	119.9	C7—N8—H83	111.0 (9)
C5—C4—C3	119.86 (13)	H81—N8—H83	105.3 (13)
C5—C4—H4	120.1	H82—N8—H83	112.5 (14)
C3—C4—H4	120.1	O11—C9—O12	126.21 (10)
C4—C5—C6	120.17 (13)	O11—C9—C10	118.96 (9)
C4—C5—H5	119.9	O12—C9—C10	114.82 (9)
C6—C5—H5	119.9	O13—C10—O14	125.88 (10)
C5—C6—C1	120.39 (13)	O13—C10—C9	121.26 (10)
C5—C6—H6	119.8	O14—C10—C9	112.84 (9)
C1—C6—H6	119.8	C10—O14—H14	111.8 (11)
N8—C7—C1	111.03 (10)
C2—C1—C7—N8	66.48 (14)	O11—C9—C10—O13	−165.04 (10)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N8—H81···O11	0.933 (17)	1.964 (17)	2.8955 (13)	176.3 (14)
N8—H82···O15^i	0.930 (16)	1.941 (16)	2.8397 (14)	161.9 (13)
N8—H83···O12^ii	0.912 (15)	1.952 (16)	2.8331 (13)	161.8 (14)
O14—H14···O12^iii	0.94 (2)	1.62 (2)	2.5583 (11)	178.0 (17)
O15—H15···O11	0.882 (17)	1.881 (17)	2.7580 (12)	172.1 (17)

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