Guanidinium benzoate

In the title compound, C₇H₅O₂^-·CH₆N₃⁺, the cation and anion lie on crystallographic mirror planes. The bond length in the deprotonated carboxyl group is intermediate between normal single and double Csp²=O bond lengths, indicating delocalization of the charge over both O atoms of the COO^- group. Hydrogen bonds assemble the ions into layers in the bc plane.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.002 Å
• R factor = 0.035
• wR factor = 0.101
• Data-to-parameter ratio = 12.6

checkCIF/PLATON results

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Alert level C
PLAT042_ALERT_1_C Calc. and Rep. MoietyFormula Strings Differ ....          ?
PLAT764_ALERT_4_C Overcomplete CIF Bond List Detected (Rep/Expd) .       1.38 Ratio

Alert level G
PLAT199_ALERT_1_G Check the Reported _cell_measurement_temperature        293 K
PLAT200_ALERT_1_G Check the Reported _diffrn_ambient_temperature .        293 K

   0 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
   2 ALERT level C = Check and explain
   2 ALERT level G = General alerts; check

   3 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   0 ALERT type 2 Indicator that the structure model may be wrong or deficient
   0 ALERT type 3 Indicator that the structure quality may be low
   1 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

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S1. Comment

Guanidine is a strong base (pK_a = 13.5) and readily reacts with all types of organic acids to give salts with good crystallinity, largely because of the presence of six potential donor sites for hydrogen-bonding interactions. From the point of view of their physical properties, guanidine compounds are potentially interesting for non-linear optics applications (Zyss et al., 1993). We are currently engaged in a research project aimed at investigating the structures and dielectric and optical properties of guanidine and guanidine derivative compounds.

Both ions of the title compound, (I) (Fig. 1), possess mirror symmetry, with atoms Cl and N2 of the cation situated in the mirror plane, as well as the carboxylate group C, the ipso-C and the para-C atoms of the anion.

The benzoate anion is almost in a planar conformation, with a dihedral angle of 0.41 (18)° between the phenyl ring and the carboxylate group.

The O—C—O angle of the carboxylate group is greater than 120° because of the steric effect of lone-pair electrons on both O atoms. The bond length in the deprotonated carboxyl group is intermediate between normal single Csp²—O (1.308–1.320 Å) and double Csp²═O bond lengths (1.214–1.224 Å) (Allen et al., 1987), indicating delocalization of the charge over both O atoms of the COO^- group.

The three C—N bond lengths in the propeller-shaped CH₆N₃⁺ cation are similar (Table 1), the symmetry of the cation being C_{3 h}. The usual model of electron delocalization in this species, leading to a C—N bond order of 1.33, is applicable here.

All H atoms of the guanidinium cation are involved in N—H···O interactions with the anion (Fig. 2, Table 2) forming layers in the bc plane, each carboxylate O atom accepting three H atoms. In each layer, the cation is bonded to three anions, two approximately perpendicular and one approximately coplanar (Fig. 3).

Related literature

For related literature, see: Allen et al. (1987); Sheldrick (1997); Zyss et al. (1993).

S2. Experimental

The title compound was prepared by adding benzoic acid (Aldrich 99.5%; 1.1 mmol) to guanidinium carbonate (Aldrich 99%; 0.55 mmol) dissolved in water (60 ml). The solution was warmed slowly and then left to evaporate under ambient conditions. After a few days, small colourless transparent single crystals of (I) were deposited.

S3. Refinement

All H atoms were located in a difference Fourier synthesis. The guanidinium H-atom coordinates were refined, with U_iso(H) = 1.2U_eq(N). The H atoms of the anion were placed in calculated positions and refined as riding on their parent atoms, with C—H = 0.93 Å and U_iso(H) = 1.2U_eq(C).

Computing details

Data collection: APEX2 (Bruker, 2005); cell refinement: APEX2; data reduction: APEX2; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 2003); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. A plot of the title compound. Displacement ellipsoids are drawn at the 50% probability level. [Symmetry codes: (a) x, 1/2 - y, z; (b) x, 3/2 - y, z.]
	Fig. 2. A packing diagram for (I), viewed down the b axis, showing the layer formation. Hydrogen bonds are shown as dashed lines.
	Fig. 3. A packing diagram for (I), viewed down the c axis, with the hydrogen bonds depicted by dashed lines.

Guanidinium benzoate

Crystal data

CH6N3^+·C7H5O2^−	F(000) = 384
Mr = 181.20	Dx = 1.194 Mg m^−3
Orthorhombic, Pnma	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2n	Cell parameters from 6505 reflections
a = 15.7347 (8) Å	θ = 2.9–23.6°
b = 8.1216 (4) Å	µ = 0.09 mm^−1
c = 7.8885 (4) Å	T = 293 K
V = 1008.08 (9) Å^3	Block, colourless
Z = 4	0.25 × 0.13 × 0.07 mm

Data collection

Bruker APEX2 CCD area-detector diffractometer	960 independent reflections
Radiation source: fine-focus sealed tube	735 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.035
φ and ω scans	θmax = 25.1°, θmin = 2.6°
Absorption correction: multi-scan (SADABS; Sheldrick, 2003)	h = −18→18
Tmin = 0.927, Tmax = 0.994	k = −9→9
27265 measured reflections	l = −9→9

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)] = 0.035	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.101	H atoms treated by a mixture of independent and constrained refinement
S = 1.04	w = 1/[σ^2(Fo^2) + (0.0512P)^2 + 0.1512P] where P = (Fo^2 + 2Fc^2)/3
960 reflections	(Δ/σ)max < 0.001
76 parameters	Δρmax = 0.09 e Å^−3
0 restraints	Δρmin = −0.16 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	0.14899 (6)	0.11435 (12)	0.01484 (12)	0.0621 (4)
C1	0.21113 (11)	0.7500	0.1719 (2)	0.0487 (5)
C2	0.11899 (11)	0.2500	0.0607 (2)	0.0466 (5)
C3	0.04384 (11)	0.2500	0.1780 (2)	0.0509 (5)
C4	0.00836 (10)	0.1032 (2)	0.2325 (2)	0.0684 (5)
H4	0.0313	0.0038	0.1962	0.082*
C5	−0.06091 (10)	0.1034 (3)	0.3405 (2)	0.0913 (6)
H5	−0.0842	0.0044	0.3773	0.110*
C6	−0.09507 (17)	0.2500	0.3930 (3)	0.0990 (10)
H6	−0.1419	0.2500	0.4650	0.119*
N1	0.23780 (9)	0.60957 (15)	0.23598 (18)	0.0634 (4)
H1A	0.2775 (10)	0.6096 (19)	0.323 (2)	0.076*
H1B	0.2182 (9)	0.521 (2)	0.191 (2)	0.076*
N2	0.15725 (12)	0.7500	0.0424 (2)	0.0648 (5)
H2	0.1368 (10)	0.848 (2)	0.0030 (19)	0.078*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0749 (7)	0.0404 (6)	0.0709 (7)	0.0054 (4)	0.0148 (5)	0.0038 (5)
C1	0.0506 (10)	0.0433 (10)	0.0520 (11)	0.000	−0.0003 (9)	0.000
C2	0.0538 (10)	0.0399 (11)	0.0462 (10)	0.000	−0.0039 (8)	0.000
C3	0.0517 (11)	0.0592 (12)	0.0418 (10)	0.000	−0.0069 (8)	0.000
C4	0.0633 (9)	0.0781 (11)	0.0638 (9)	−0.0054 (7)	0.0006 (7)	0.0148 (8)
C5	0.0696 (11)	0.1285 (17)	0.0757 (12)	−0.0177 (11)	0.0059 (9)	0.0298 (12)
C6	0.0653 (16)	0.170 (3)	0.0618 (16)	0.000	0.0113 (12)	0.000
N1	0.0737 (9)	0.0417 (7)	0.0748 (9)	0.0040 (6)	−0.0205 (7)	−0.0017 (6)
N2	0.0758 (12)	0.0506 (11)	0.0680 (11)	0.000	−0.0234 (10)	0.000

Geometric parameters (Å, º)

O1—C2	1.2519 (13)	C4—H4	0.9300
C1—N1^i	1.3162 (15)	C5—C6	1.371 (2)
C1—N1	1.3162 (15)	C5—H5	0.9300
C1—N2	1.328 (3)	C6—C5^ii	1.371 (2)
C2—O1^ii	1.2519 (13)	C6—H6	0.9300
C2—C3	1.502 (3)	N1—H1A	0.931 (18)
C3—C4	1.3846 (17)	N1—H1B	0.860 (17)
C3—C4^ii	1.3846 (17)	N2—H2	0.915 (18)
C4—C5	1.383 (2)
N1^i—C1—N1	120.12 (18)	C3—C4—H4	119.7
N1^i—C1—N2	119.94 (9)	C6—C5—C4	119.7 (2)
N1—C1—N2	119.94 (9)	C6—C5—H5	120.1
O1^ii—C2—O1	123.29 (17)	C4—C5—H5	120.1
O1^ii—C2—C3	118.35 (9)	C5^ii—C6—C5	120.6 (2)
O1—C2—C3	118.35 (9)	C5^ii—C6—H6	119.7
C4—C3—C4^ii	118.83 (19)	C5—C6—H6	119.7
C4—C3—C2	120.58 (10)	C1—N1—H1A	119.9 (10)
C4^ii—C3—C2	120.59 (10)	C1—N1—H1B	117.1 (11)
C5—C4—C3	120.54 (17)	H1A—N1—H1B	123.0 (15)
C5—C4—H4	119.7	C1—N2—H2	119.1 (10)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···O1^iii	0.931 (18)	1.902 (19)	2.8309 (17)	175.1 (14)
N2—H2···O1^iv	0.915 (18)	2.171 (19)	2.9700 (10)	145.4 (14)
N1—H1B···O1^ii	0.860 (17)	2.081 (17)	2.8816 (17)	154.7 (15)

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