Zwitterionic 2-guanidinium-1-amino­carboxyl­ate monohydrate

It is found that the commercial product with formula C₂H₈N₄O₃, supposedly amino­guanidinium hydrogen carbon­ate, is actually a monohydrate of amino­guanidinium betaine. In the zwitterion, the guanidinium and NHCO₂ groups are planar and nearly perpendicular to each other, with a dihedral angle of 83.26 (5)°. The crystal structure can be thought of as composed of layers of organic molecules alternating with layers of water molecules. The structural units are held together by an extensive hydrogen-bonding network.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](N-C) = 0.002 Å
• R factor = 0.040
• wR factor = 0.115
• Data-to-parameter ratio = 15.0

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry

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S1. Comment

The two protonated forms of a strong base aminoguanidine are described: monoprotonated (Adams, 1977) and diprotonated (Ross et al. 1999). In the course of our study of guanidinium derivatives, several salts with squaric acid have been investigated by means of vibrational (IR and Raman) spectroscopy and single-crystal analysis (Kolev, Glavcheva et al., 1997; Kolev, Preut et al., 1997; Kolev et al., 1997a,b). One of these compounds, aminoguanidinium squarate, has been synthesized using the commercial products aminoguanidinium hydrogen carbonate (AGHC) (FLUKA, EGA Chemie, ALDRICH) and squaric acid (Huels-Marl, Germany).

The vibrational spectra of AGHC differ significantly from the expected ones, although that compound produces the aminoguanidinium cation and this is unambiguously pointed out by crystal structure of aminoguanidinium squarate (Kolev, Glavcheva et al., 1997). In the IR spectra of AGHC, there are no characteristic bands for the hydrogen carbonate anion and, in addition, two strong bands at 1688 and 1634 cm⁻¹ appear. We compared our spectra with that of aminoguanidinium chloride, which could be used as a model system for IR study of the aminoguanidinium cation. There are seven ν(N—H) bands in the IR spectrum of aminoguanidinium chloride and only five in the spectrum of AGHC. These discrepancies motivated us to calculate the theoretical spectrum of aminoguanidinium cation on ab initio RHF 6–31G* and DFT B3LYP 6–31G* levels. The obtained theoretical frequencies proved our assumption that the commercial product is not AGHC. The assignment of the bands in IR and RAMAN spectra of the studied product is better in accordance with the literature data for different betaines (Szafran & Koput, 1996; Viertorinne et al., 1999). The detailed vibrational and quantum chemical investigation is in progress and will be published later.

There is no entry in the literature for the compound studied (CSD, Beilstein and Chemical Abstracts). That was the reason to undertake the present determination of molecular and crystal structure of AGHC, (I).

The molecule of (I) could be regarded as a derivative of aminoguanidinium, where the positive charge is delocalized over the guanidinium moiety and the negative charge over the –NHCO₂ group (Fig. 1). This is corroborated by the solid-state IR spectrum (KBr pellet). The guanidinium and –NHCO₂ groups are planar and nearly perpendicular to each other, with a dihedral angle of 83.26 (5)°. An extensive hydrogen-bonding network holds the structural units together (Fig. 2). The inner guanidile atoms H32 and H42 form N—H···O bonds through which the organic molecules are connected to form zigzag chains parallel to the c axis. The chains are linked along the b axis and thus a layer perpendicular to the a axis is formed. The water molecule is a donor of two and an acceptor of two hydrogen bonds, which hold the layers along the a axis. The crystal structure can be thought as a layered one, where layers of organic molecules alternate with those formed by water molecules only.

S2. Experimental

The commercial product is a gray powder. It was recrystallized four times, first from water–ethanol and three times from doubly distilled water. The IR and Raman spectra of the compound were measured after each recrystallization and they show that the compound remained unchanged. Prismatic and colorles single crystals suitable for X-ray analysis were grown from doubly distilled water at room temperature.

S3. Refinement

All of the H atoms were found from a difference Fourier map and their positions were freely refined.

Computing details

Data collection: CAD-4 Software (Enraf-Nonius, 1989); cell refinement: CAD-4 Software; data reduction: DATARED (P. Vasilev, unpublished); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPII (Johnson, 1976).

Figures

	Fig. 1. Fig, 1. The structural units of (I), with labelling of the non-H atoms. Displacement ellipsoids are shown at the 50% probability level.
	Fig. 2. Fig, 2. The three-dimensional packing of the structural units in (I). Hydrogen bonds are shown as dotted lines.

betaine of aminoguanidine monohydrate

Crystal data

C2H6N4O2·H2O	F(000) = 288
Mr = 136.12	Dx = 1.537 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71065 Å
Hall symbol: -P 2ybc	Cell parameters from 22 reflections
a = 9.1929 (8) Å	θ = 20.0–21.9°
b = 4.8380 (5) Å	µ = 0.14 mm^−1
c = 13.2467 (11) Å	T = 293 K
β = 93.073 (7)°	Plate, colorless
V = 588.30 (9) Å^3	0.26 × 0.26 × 0.13 mm
Z = 4

Data collection

Enraf-Nonius CAD-4 diffractometer	Rint = 0.029
Radiation source: fine-focus sealed tube	θmax = 29.9°, θmin = 2.2°
Graphite monochromator	h = 0→12
ω–2θ scans	k = −6→6
3408 measured reflections	l = −18→18
1708 independent reflections	3 standard reflections every 500 reflections
1230 reflections with I > 2σ(I)	intensity decay: 1.0%

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)] = 0.040	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.115	All H-atom parameters refined
S = 1.01	w = 1/[σ^2(Fo^2) + (0.0625P)^2 + 0.0484P] where P = (Fo^2 + 2Fc^2)/3
1708 reflections	(Δ/σ)max = 0.001
114 parameters	Δρmax = 0.21 e Å^−3
0 restraints	Δρmin = −0.32 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. 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
O1	0.91386 (10)	0.0148 (2)	0.84477 (7)	0.0344 (2)
O2	0.69999 (10)	−0.1364 (2)	0.77694 (7)	0.0357 (3)
N1	0.84970 (12)	0.1234 (3)	0.68527 (8)	0.0328 (3)
N2	0.74819 (12)	0.1392 (2)	0.60465 (8)	0.0313 (3)
C2	0.76125 (13)	−0.0251 (2)	0.52446 (9)	0.0260 (3)
N3	0.66894 (13)	0.0084 (3)	0.44530 (9)	0.0348 (3)
N4	0.86175 (13)	−0.2191 (3)	0.52504 (9)	0.0334 (3)
C1	0.81807 (13)	−0.0048 (3)	0.77411 (9)	0.0263 (3)
O	0.45668 (11)	0.4313 (2)	0.36741 (8)	0.0369 (3)
H11	0.9232 (19)	0.233 (4)	0.6871 (12)	0.040 (4)*
H31	0.6018 (18)	0.137 (4)	0.4419 (12)	0.040 (4)*
H32	0.6793 (19)	−0.107 (4)	0.3876 (14)	0.050 (5)*
H21	0.679 (2)	0.265 (4)	0.6026 (13)	0.048 (5)*
H1	0.531 (2)	0.485 (4)	0.3316 (14)	0.058 (6)*
H2	0.401 (2)	0.324 (5)	0.3164 (15)	0.062 (6)*
H41	0.8751 (18)	−0.323 (4)	0.4674 (14)	0.045 (5)*
H42	0.926 (2)	−0.247 (4)	0.5787 (13)	0.047 (5)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0311 (5)	0.0441 (6)	0.0272 (5)	−0.0031 (4)	−0.0056 (4)	−0.0013 (4)
O2	0.0282 (5)	0.0453 (6)	0.0332 (5)	−0.0086 (4)	−0.0007 (4)	0.0010 (4)
N1	0.0294 (5)	0.0408 (6)	0.0275 (5)	−0.0092 (5)	−0.0052 (4)	0.0033 (4)
N2	0.0327 (5)	0.0334 (6)	0.0272 (5)	0.0053 (5)	−0.0051 (4)	−0.0008 (4)
C2	0.0246 (5)	0.0273 (6)	0.0259 (5)	−0.0025 (4)	0.0001 (4)	0.0046 (4)
N3	0.0353 (6)	0.0392 (6)	0.0291 (6)	0.0082 (5)	−0.0069 (5)	−0.0002 (5)
N4	0.0319 (6)	0.0376 (6)	0.0301 (5)	0.0089 (5)	−0.0033 (4)	−0.0006 (5)
C1	0.0239 (5)	0.0284 (6)	0.0265 (6)	0.0015 (4)	0.0011 (4)	−0.0029 (4)
O	0.0334 (5)	0.0378 (5)	0.0394 (5)	−0.0024 (4)	0.0005 (4)	−0.0043 (4)

Geometric parameters (Å, º)

O1—C1	1.2538 (15)	C2—N3	1.3231 (16)
O2—C1	1.2607 (15)	N3—H31	0.876 (18)
N1—C1	1.3751 (17)	N3—H32	0.954 (19)
N1—N2	1.3822 (15)	N4—H41	0.928 (19)
N1—H11	0.859 (18)	N4—H42	0.911 (19)
N2—C2	1.3373 (16)	O—H1	0.89 (2)
N2—H21	0.879 (19)	O—H2	0.98 (2)
C2—N4	1.3167 (16)
C1—N1—N2	121.42 (11)	C2—N3—H32	118.4 (10)
C1—N1—H11	117.2 (11)	H31—N3—H32	118.2 (15)
N2—N1—H11	119.0 (11)	C2—N4—H41	120.4 (11)
C2—N2—N1	119.69 (11)	C2—N4—H42	122.5 (11)
C2—N2—H21	118.9 (11)	H41—N4—H42	116.9 (15)
N1—N2—H21	121.2 (11)	O1—C1—O2	125.98 (12)
N4—C2—N3	120.78 (12)	O1—C1—N1	115.62 (11)
N4—C2—N2	120.79 (11)	O2—C1—N1	118.36 (11)
N3—C2—N2	118.41 (12)	H1—O—H2	100.4 (16)
C2—N3—H31	123.2 (10)
C2—N1—N2—C1	104.50 (15)	N2—C1—N3—N4	122.43 (14)
N1—N2—C1—N3	−120.61 (18)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H11···O1^i	0.85 (1)	2.08 (2)	2.926 (2)	166 (2)
N3—H31···O	0.87 (1)	2.15 (2)	2.974 (2)	155 (1)
N3—H32···O2^ii	0.95 (1)	1.94 (2)	2.892 (2)	176 (2)
N2—H21···O^iii	0.89 (2)	1.98 (2)	2.842 (2)	166 (2)
O—H1···O2^iv	0.89 (2)	1.89 (2)	2.777 (2)	170 (2)
O—H2···O2^v	0.98 (2)	1.75 (2)	2.733 (1)	179 (2)
N4—H41···O1^ii	0.93 (2)	1.92 (2)	2.846 (2)	175 (2)
N4—H42···O1^vi	0.91 (2)	2.09 (2)	2.916 (2)	151 (2)

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