Biguanidinium dichloride

Gustavo Portalone

doi:10.1107/S1600536808006144

. 2008 Mar 7;64(Pt 4):o683. doi: 10.1107/S1600536808006144

Biguanidinium dichloride

Gustavo Portalone ^a,^*

PMCID: PMC2960918 PMID: 21202075

Abstract

The asymmetric unit of the title compound, C₂H₉N₅ ²⁺·2Cl⁻, is composed of one diprotonated biguanidinium cation and two chloride anions. The diprotonated cation consists of two planar halves twisted by 36.42 (6)°. The ions are associated in the crystal structure by extensive hydrogen bonding into a three-dimensional network; the diprotonated biguanidinium cation is hydrogen bonded to the chloride anions.

Related literature

For a general approach to the use of multiple-hydrogen-bonding DNA/RNA nucleobases as potential supramolecular reagents, see: Portalone & Colapietro (2004 ▶, 2007 ▶ and references therein). For related crystal structures, see: Ernst (1977 ▶); Pinkerton & Schwarzenbach (1978 ▶); Martin & Pinkerton (1996 ▶); Martin et al. (1996 ▶, 1997 ▶); Kurzer & Pitchfork (1968 ▶).

Experimental

Crystal data

C₂H₉N₅ ²⁺·2Cl⁻
M _r = 174.04
Monoclinic,
a = 6.43693 (9) Å
b = 16.93420 (18) Å
c = 6.65260 (8) Å
β = 98.6878 (12)°
V = 716.84 (1) Å³
Z = 4
Mo Kα radiation
μ = 0.83 mm⁻¹
T = 298 (2) K
0.20 × 0.20 × 0.15 mm

Data collection

Oxford Diffraction Xcalibur S CCD diffractometer
Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2006 ▶) T _min = 0.852, T _max = 0.886
80724 measured reflections
2456 independent reflections
2349 reflections with I > 2σ(I)
R _int = 0.020

Refinement

R[F ² > 2σ(F ²)] = 0.027
wR(F ²) = 0.070
S = 1.14
2456 reflections
119 parameters
All H-atom parameters refined
Δρ_max = 0.14 e Å⁻³
Δρ_min = −0.14 e Å⁻³

Data collection: CrysAlis CCD (Oxford Diffraction, 2006 ▶; cell refinement: CrysAlis RED (Oxford Diffraction, 2006 ▶; data reduction: CrysAlis RED; program(s) used to solve structure: SIR97 (Altomare et al., 1999 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: ORTEP-3 (Farrugia, 1997 ▶); software used to prepare material for publication: WinGX (Farrugia, 1999 ▶).

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536808006144/kp2161sup1.cif

e-64-0o683-sup1.cif^{(14.3KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536808006144/kp2161Isup2.hkl

e-64-0o683-Isup2.hkl^{(118.2KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1⋯Cl2	0.819 (18)	2.279 (18)	3.0796 (9)	166.0 (16)
N2—H21⋯Cl1ⁱ	0.833 (18)	2.530 (18)	3.2557 (10)	146.4 (15)
N2—H22⋯Cl2ⁱⁱ	0.852 (19)	2.34 (2)	3.1714 (10)	167.1 (17)
N3—H31⋯Cl2ⁱ	0.823 (19)	2.787 (19)	3.5098 (12)	147.8 (16)
N3—H32⋯Cl1ⁱⁱⁱ	0.857 (19)	2.599 (19)	3.1933 (10)	127.4 (15)
N3—H32⋯Cl2	0.857 (19)	2.835 (19)	3.5454 (12)	141.3 (15)
N4—H41⋯Cl1	0.88 (2)	2.703 (19)	3.4178 (11)	139.4 (16)
N4—H42⋯Cl1^iv	0.846 (19)	2.412 (19)	3.2295 (10)	162.8 (17)
N5—H51⋯Cl2^v	0.853 (19)	2.413 (19)	3.2404 (12)	163.7 (16)
N5—H52⋯Cl1	0.874 (19)	2.369 (19)	3.1905 (11)	156.7 (17)

Open in a new tab

Symmetry codes: (i) Inline graphic ; (ii) ; (iii) ; (iv) ; (v) .

Acknowledgments

We thank MIUR (Rome) for 2006 financial support of the project ‘X-ray diffractometry and spectrometry’.

supplementary crystallographic information

Comment

Biguanidine derivatives, characterized by multiple hydrogen-bond donor sites, are good candidates to be coupled in the crystal with carefully selected molecules having multiple hydrogen-bond acceptor sites (Portalone & Colapietro, 2004, 2007). As a part of a more general study of multiple-hydrogen-bonding DNA/RNA nucleobases as potential supramolecular reagents, this paper reports the crystal structure of the title compound, (I), BIGH₂²⁺2Cl^-. The asymmetric unit of (I) (Fig. 1) consists of a diprotonated biguanidinium cation (BIGH₂²⁺) and two chloride anions; protonation occurs at the bridge N atom and the imino N atom of the biguanidine molecule. The structure of the delocalized cation is very similar to those previously reported for the carbonate (BIGH₂)CO₃ and the sulfates (BIGH₂)SO₄.2H₂O and (BIGH₂)SO₄.H₂O (Pinkerton & Schwarzenbach, 1978), the dinitrate (BIGH₂)NO₃ (Martin et al., 1996), the diperchlorate (BIGH₂)2ClO₄ (Martin & Pinkerton, 1996), the bis-dinitramide (BIGH₂)(DN)₂ and (BIGH₂)(DN)₂.H₂O (Martin et al., 1997). BIGH₂²⁺ is composed of two planar halves sharing the atom N(1). These two planar parts are twisted with respect to each other by 36.42 (6)°. The C—N terminal bond lengths are shorter due to delocalization of π-electron density through the planar fragments. The lack of complete planarity of the cation is due to steric interaction between the hydrogen atoms. This interaction induces a strain in the molecule which is manifested by the opening of the angle at the bridging N atom [C1—N1—C2, 127.9 (1)°]. The weakening of the bridges bonds is due to the lowered basicity of the bridge N atom on protonation [pk_a^I = 11.5; pk_a^II = 2.9 (Kurzer & Pitchfork, 1968)] and is manifested by the longer C—N1 bridging bonds [1.363 (1) - 1.372 (1) Å] and the shorter terminal C—N bonds [1.306 (1) - 1.321 (1) Å], comparing with the corresponding ones reported for BIGH⁺Cl^- (Ernst, 1977). Analysis of the crystal packing of (I) (Fig. 2) shows that the structure is stabilized by ten hydrogen bonds N—H···Cl^- involving all protons (Table 1) which account for the relatively high density (D_x = 1.61 Mg m^-3).

Experimental

Biguanide (0.1 mmol, Sigma Aldrich at 98% purity) was dissolved in water (9 ml) and heated under reflux for 2 h. After cooling a solution to an ambient temperature, while stirring, HCl (6 mol L^-1) was added dropwise until the pH = 2. Crystals suitable for single-crystal X-ray diffraction were obtained by slow evaporation of the solvent after a few days.