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Acta Cryst. (2008). E64, o683    [ doi:10.1107/S1600536808006144 ]

Biguanidinium dichloride

G. Portalone

Abstract top

The asymmetric unit of the title compound, C2H9N52+·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.

Comment top

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 [pkaI = 11.5; pkaII = 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 (Dx = 1.61 Mg m-3).

Related literature top

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).

For related literature, see: Kurzer & Pitchfork (1968).

Experimental top

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.

Refinement top

All H atoms were found in a difference map and refined isotropically.

Computing details top

Data collection: CrysAlis CCD (Oxford Diffraction, 2006); cell refinement: CrysAlis RED (Oxford Diffraction, 2006); data reduction: CrysAlis RED (Oxford Diffraction, 2006); 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).

Figures top
[Figure 1] Fig. 1. The molecular structure of (I) showing the atom-labelling scheme. Displacements ellipsoids are at the 50% probability level.
[Figure 2] Fig. 2. Crystal packing diagram for (I) viewed approximately down a. All atoms are shown as small spheres of arbitrary radii. Hydrogen bonding is indicated by dashed lines.
Biguanidinium dichloride top
Crystal data top
C2H9N52+·2Cl–F000 = 360
Mr = 174.04Dx = 1.613 Mg m−3
Monoclinic, P21/cMo Kα radiation
λ = 0.71073 Å
Hall symbol: -P 2ybcCell parameters from 80724 reflections
a = 6.43693 (9) Åθ = 3.2–32.0º
b = 16.93420 (18) ŵ = 0.83 mm−1
c = 6.65260 (8) ÅT = 298 (2) K
β = 98.6878 (12)ºPlate, colourless
V = 716.841 (15) Å30.20 × 0.20 × 0.15 mm
Z = 4
Data collection top
Oxford Diffraction Xcalibur S CCD
diffractometer		2456 independent reflections
Radiation source: Enhance (Mo) X-ray source2349 reflections with I > 2σ(I)
Monochromator: graphiteRint = 0.020
Detector resolution: 16.0696 pixels mm-1θmax = 32.0º
T = 298(2) Kθmin = 3.2º
ω and φ scansh = −9→9
Absorption correction: multi-scan
(CrysAlis RED; Oxford Diffraction, 2006)		k = −25→25
Tmin = 0.852, Tmax = 0.886l = −9→9
80724 measured reflections
Refinement top
Refinement on F2Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: fullAll H-atom parameters refined
R[F2 > 2σ(F2)] = 0.027  w = 1/[σ2(Fo2) + (0.0293P)2 + 0.2376P]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.071(Δ/σ)max < 0.001
S = 1.14Δρmax = 0.14 e Å−3
2456 reflectionsΔρmin = −0.14 e Å−3
119 parametersExtinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.110 (6)
Secondary atom site location: difference Fourier map
Crystal data top
C2H9N52+·2Cl–V = 716.841 (15) Å3
Mr = 174.04Z = 4
Monoclinic, P21/cMo Kα
a = 6.43693 (9) ŵ = 0.83 mm−1
b = 16.93420 (18) ÅT = 298 (2) K
c = 6.65260 (8) Å0.20 × 0.20 × 0.15 mm
β = 98.6878 (12)º
Data collection top
Oxford Diffraction Xcalibur S CCD
diffractometer		2456 independent reflections
Absorption correction: multi-scan
(CrysAlis RED; Oxford Diffraction, 2006)		2349 reflections with I > 2σ(I)
Tmin = 0.852, Tmax = 0.886Rint = 0.020
80724 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.027119 parameters
wR(F2) = 0.071All H-atom parameters refined
S = 1.14Δρmax = 0.14 e Å−3
2456 reflectionsΔρmin = −0.14 e Å−3
Special details top

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 (Å2) top
xyzUiso*/Ueq
Cl10.86502 (5)−0.053995 (15)0.27026 (4)0.03288 (9)
Cl20.62775 (5)0.315420 (18)0.37349 (5)0.03605 (9)
N10.35152 (13)0.16618 (5)0.32041 (15)0.02556 (17)
H10.430 (3)0.2034 (10)0.356 (3)0.039 (4)*
N20.00539 (15)0.12772 (6)0.20409 (16)0.02955 (19)
H210.025 (3)0.0812 (11)0.243 (3)0.038 (4)*
H22−0.109 (3)0.1408 (11)0.130 (3)0.048 (5)*
N30.09938 (18)0.25798 (6)0.21118 (17)0.0335 (2)
H31−0.025 (3)0.2708 (11)0.195 (3)0.046 (5)*
H320.193 (3)0.2941 (11)0.232 (3)0.044 (5)*
N40.38953 (17)0.03968 (6)0.18533 (15)0.0304 (2)
H410.461 (3)−0.0045 (12)0.196 (3)0.050 (5)*
H420.308 (3)0.0513 (11)0.078 (3)0.047 (5)*
N50.62338 (15)0.08686 (7)0.45410 (16)0.0324 (2)
H510.646 (3)0.1178 (11)0.556 (3)0.044 (5)*
H520.711 (3)0.0485 (11)0.440 (3)0.051 (5)*
C10.14797 (15)0.18273 (5)0.24248 (14)0.02118 (17)
C20.45468 (15)0.09538 (6)0.31785 (15)0.02354 (18)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Cl10.04007 (15)0.02213 (13)0.03406 (15)0.00402 (9)−0.00208 (10)−0.00296 (9)
Cl20.03243 (14)0.03940 (16)0.03375 (15)−0.01269 (10)−0.00333 (10)0.00083 (10)
N10.0205 (4)0.0213 (4)0.0344 (4)−0.0012 (3)0.0024 (3)−0.0021 (3)
N20.0220 (4)0.0256 (4)0.0390 (5)−0.0017 (3)−0.0020 (3)0.0058 (4)
N30.0368 (5)0.0215 (4)0.0420 (6)0.0052 (4)0.0055 (4)0.0047 (4)
N40.0379 (5)0.0269 (4)0.0257 (4)0.0089 (4)0.0022 (4)−0.0017 (3)
N50.0253 (4)0.0399 (5)0.0312 (5)0.0067 (4)0.0010 (3)0.0010 (4)
C10.0229 (4)0.0203 (4)0.0208 (4)0.0012 (3)0.0047 (3)0.0022 (3)
C20.0218 (4)0.0261 (4)0.0238 (4)0.0022 (3)0.0068 (3)0.0031 (3)
Geometric parameters (Å, °) top
N1—C11.3634 (13)N3—H320.857 (19)
N1—C21.3719 (13)N4—C21.3156 (14)
N1—H10.819 (18)N4—H410.88 (2)
N2—C11.3056 (13)N4—H420.846 (19)
N2—H210.833 (18)N5—C21.3131 (14)
N2—H220.852 (19)N5—H510.853 (19)
N3—C11.3211 (13)N5—H520.874 (19)
N3—H310.823 (19)
C1—N1—C2127.89 (9)H41—N4—H42121.2 (17)
C1—N1—H1117.6 (12)C2—N5—H51120.4 (12)
C2—N1—H1113.6 (12)C2—N5—H52119.2 (13)
C1—N2—H21122.9 (12)H51—N5—H52120.4 (17)
C1—N2—H22116.6 (13)N2—C1—N3120.97 (10)
H21—N2—H22120.4 (17)N2—C1—N1122.31 (9)
C1—N3—H31118.5 (13)N3—C1—N1116.70 (9)
C1—N3—H32121.3 (12)N5—C2—N4122.04 (10)
H31—N3—H32119.0 (17)N5—C2—N1116.03 (10)
C2—N4—H41116.7 (12)N4—C2—N1121.93 (9)
C2—N4—H42119.7 (12)
C2—N1—C1—N219.96 (17)C1—N1—C2—N5−159.12 (10)
C2—N1—C1—N3−161.49 (10)C1—N1—C2—N421.55 (17)
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
N1—H1···Cl20.819 (18)2.279 (18)3.0796 (9)166.0 (16)
N2—H21···Cl1i0.833 (18)2.530 (18)3.2557 (10)146.4 (15)
N2—H22···Cl2ii0.852 (19)2.34 (2)3.1714 (10)167.1 (17)
N3—H31···Cl2i0.823 (19)2.787 (19)3.5098 (12)147.8 (16)
N3—H32···Cl1iii0.857 (19)2.599 (19)3.1933 (10)127.4 (15)
N3—H32···Cl20.857 (19)2.835 (19)3.5454 (12)141.3 (15)
N4—H41···Cl10.88 (2)2.703 (19)3.4178 (11)139.4 (16)
N4—H42···Cl1iv0.846 (19)2.412 (19)3.2295 (10)162.8 (17)
N5—H51···Cl2v0.853 (19)2.413 (19)3.2404 (12)163.7 (16)
N5—H52···Cl10.874 (19)2.369 (19)3.1905 (11)156.7 (17)
Symmetry codes: (i) x−1, y, z; (ii) x−1, −y+1/2, z−1/2; (iii) −x+1, y+1/2, −z+1/2; (iv) −x+1, −y, −z; (v) x, −y+1/2, z+1/2.
Table 1
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
N1—H1···Cl20.819 (18)2.279 (18)3.0796 (9)166.0 (16)
N2—H21···Cl1i0.833 (18)2.530 (18)3.2557 (10)146.4 (15)
N2—H22···Cl2ii0.852 (19)2.34 (2)3.1714 (10)167.1 (17)
N3—H31···Cl2i0.823 (19)2.787 (19)3.5098 (12)147.8 (16)
N3—H32···Cl1iii0.857 (19)2.599 (19)3.1933 (10)127.4 (15)
N3—H32···Cl20.857 (19)2.835 (19)3.5454 (12)141.3 (15)
N4—H41···Cl10.88 (2)2.703 (19)3.4178 (11)139.4 (16)
N4—H42···Cl1iv0.846 (19)2.412 (19)3.2295 (10)162.8 (17)
N5—H51···Cl2v0.853 (19)2.413 (19)3.2404 (12)163.7 (16)
N5—H52···Cl10.874 (19)2.369 (19)3.1905 (11)156.7 (17)
Symmetry codes: (i) x−1, y, z; (ii) x−1, −y+1/2, z−1/2; (iii) −x+1, y+1/2, −z+1/2; (iv) −x+1, −y, −z; (v) x, −y+1/2, z+1/2.
Acknowledgements top

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

references
References top

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