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Benzamidinium tetra­chloro­gallate(III)

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aAssociated Octel Co. Ltd, Ellesmere Port, South Wirral L65 3HF, England, and bDepartment of Chemistry, University of Warwick, Coventry CV4 7AL, England
*Correspondence e-mail: barkerj@octel-corp.com

(Received 9 March 2005; accepted 17 March 2005; online 31 March 2005)

The synthesis of the title compound, (C7H9N2)[GaCl4], is described. The N—C—N fragment involves delocalized bonding, which does not extend to the adjacent C—C bond. The N—C—N plane is aligned at 39.6 (2)° to the mean plane through the phenyl group. The GaCl4 anion is tetrahedral, with Ga—Cl bonds in the range 2.165 (1)–2.180 (1) Å. Intermolecular hydrogen bonding is postulated between the N and Cl atoms.

Comment

Interest in the pharmaceutical effects provided by gallium and amidine ligands (Yoshida et al., 2004[Yoshida, K., Nakagawa, T. & Kayahara, T. (2004). US Patent No. 6 784 191.]) continues, particularly with regard to antiviral and antitumour activity (Fimiani et al., 1990[Fimiani, V., Ainis, T., Cavellero, A. & Piraino, P. (1990). J. Chemother. 2, 319-326.]; Sharma et al., 1997[Sharma, V., Beatty, A., Goldberg, D. E. & Piwnica-Worms, D. (1997). J. Chem. Soc. Chem. Commun. pp. 2223-2224.]; Kratz et al., 1992[Kratz, F., Nuber, B., Weiss, J. & Keppler, B. K. (1992). Polyhedron, 11, 487-498.]). This fact has directed us to extend our previous work in the area (Barker et al., 1996[Barker, J., Phillips, P. R., Wallbridge, M. G. H. & Powell, H. R. (1996). Acta Cryst. C52, 2617-2619.]) to encompass systems containing gallium chloride and the amidinium ion. The crystal structure of the title compound, (I[link]), has been determined since it affords an opportunity to study the structural features of a benzamidinium cationic system, which has no substituents on the N atoms, in combin­ation with the tetra­chloro­gallate anion.[link]

[Scheme 1]

The molecular structure of (I[link]) is shown in Fig. 1[link] and selected geometric parameters are listed in Table 1[link]. The benz­amidine, in its cationic form, shows protonation at the imino N atom, yielding a more delocalized N—C—N fragment [C—N = 1.304 (5) and 1.317 (5) Å] than found in the parent benz­amidine [1.294 (3) and 1.344 (3) Å; Barker et al., 1996[Barker, J., Phillips, P. R., Wallbridge, M. G. H. & Powell, H. R. (1996). Acta Cryst. C52, 2617-2619.]], but similar to those found in benzamidinium acetyl­acetonatotetra­carbonyl­rhenate(II) (Lenhert et al., 1984[Lenhert, P. G., Lukehart, C. M., Sotiropoulos, P. D. & Srinivasan, K. (1984). Inorg. Chem. 23, 1807-1810.]). The C—Camidine distances of the parent amidine [1.489 (3) Å; Barker et al., 1996[Barker, J., Phillips, P. R., Wallbridge, M. G. H. & Powell, H. R. (1996). Acta Cryst. C52, 2617-2619.]] and the cation [1.475 (5) Å] show little difference, indicating that the delocalization is restricted to the N—C—N fragment. The latter point is confirmed by the C6—C1—C7—N1 torsion angle of 140.1 (4)°, which shows that the cation is non-planar and thus involves a C1—C7 single bond. The angle between the N—C—N unit and the mean plane through the benzene ring is 39.6 (2)° and compares favourably with that reported previously in benz­amidine hydro­chloride monohydrate [36.6 (8)°; Thailambal et al., 1986[Thailambal, V. G., Pattabhi, V. & Guru Row, T. N. (1986). Acta Cryst. C42, 587-589.]]. In the N—C—N group, a three-centre four π-electron system (Kapp et al., 1996[Kapp, J., Schade, C., El-Nahasa, A. & Schleyer, P. v. R. (1996). Angew. Chem. Int. Ed. Engl. 35, 2236-2238.]), the stable benzamidinium fragment is reliant on the π-donation of the nitro­gen lone pair into the formally unfilled 2p π orbital of the adjacent carbon centre, which compensates for the σ-attracting effect from the electronegativity of the nitro­gen. The planarity contrasts with the situation calculated for the theoretical di­phospho­rus analogue, which has proven to be an elusive synthetic goal (Kato et al., 2002[Kato, T., Gornitzka, H., Baceiredo, A., Schoeller, W. W & Bertrand, G. (2002). J. Am. Chem. Soc. 124, 2506-2512.]).

The GaCl4 anion is essentially tetrahedral, with Ga—Cl distances (Table 1[link]) within the expected range; an examination of the Cambridge Structural Database (Version 5.23; Allen, 2002[Allen, F. H. (2002). Acta Cryst. B58, 380-388.]; Fletcher et al., 1996[Fletcher, D. A., McMeeking, R. F. & Parkin, D. (1996). J. Chem. Inf. Comput. Sci. 36, 746-749.]) shows that, for 37 structures containing the GaCl4 unit (e.g. Hausen et al., 1978[Hausen, H. D., Binder, H. & Schwarz, W. (1978). Z. Naturforsch. Teil B, 33, 567-569.]; Jakubas et al., 1997[Jakubas, R., Bator, G., Gosniowska, M., Ciunik, Z., Baran, J. & Lefebvre, J. (1997). J. Phys. Chem. Solids, 58, 989-998.]), the average Ga—Cl bond length is 2.162 (12) Å, with a range from 2.087 to 2.222 Å.

Varying degrees of hydrogen bonding between the NH groups and the Cl atoms is indicated from an examination of the intermolecular geometry (Table 2[link]). The observed N⋯Cl separations (with the exception of that between N2 and Cl2) are comparable with the sum of the van der Waals radii for nitro­gen and chlorine (1.55 + 1.75 = 3.30 Å), whilst the N—H⋯Cl angles are approximately as expected for conventional two-centre hydrogen bonding. Thus, it would appear that the packing in this structure is significantly influenced by the hydrogen bonding; this effect would be absent in N-substituted benzamidinium systems.

[Figure 1]
Figure 1
The asymmetric unit of (I[link]), showing the atomic numbering. Displacement ellipsoids are drawn at the 50% probability level for non-H atoms and H atoms are shown as spheres of arbitrary radii.

Experimental

An­hydro­us gallium(III) chloride (1.33 g, 7.6 mmol) was weighed into a round-bottomed flask containing dry toluene (100 ml) and then benz­amidine hydro­chloride (2.40 g, 15.4 mmol) was added. The resultant suspension was refluxed for 2 h. The solution was filtered hot through a No. 3 frit under nitro­gen into a Schlenk tube. The solvent was removed by slow nitro­gen flow to yield white crystals [yield 0.14 g, 6%; m.p. (DSC) 394 K]. Calculated for C7H8Cl4GaN2: C 25.35; H 2.43; N 8.45; found: C 25.42; H 2.93; N 8.62%. 13C NMR (50.3 MHz, D2O): δ 167.0 (N—C—N), 136.2, 131.4, 130.8, 129.4 (Ar). 1H NMR (200 MHz, D2O): δ 7.52–6.72. IR: 3415 (vs broad), 1688 (s), 1642 (s), 1161 (s), 778 (s), 691 (s).

Crystal data
  • (C7H9N2)[GaCl4]

  • Mr = 332.68

  • Monoclinic, P21/c

  • a = 13.986 (2) Å

  • b = 10.8228 (19) Å

  • c = 9.0976 (16) Å

  • β = 108.474 (4)°

  • V = 1306.1 (4) Å3

  • Z = 4

  • Dx = 1.692 Mg m−3

  • Mo Kα radiation

  • Cell parameters from 3209 reflections

  • θ = 2.4–28.0°

  • μ = 2.89 mm−1

  • T = 180 (2) K

  • Needle, white

  • 0.38 × 0.06 × 0.06 mm

Data collection
  • Bruker SMART CCD area-detector diffractometer

  • ω scans

  • Absorption correction: multi-scan (SADABS; Sheldrick, 1996[Sheldrick, G. M. (1996). SADABS. University of Göttingen, Germany.]) Tmin = 0.406, Tmax = 0.846

  • 7620 measured reflections

  • 3024 independent reflections

  • 1892 reflections with I > 2σ(I)

  • Rint = 0.050

  • θmax = 28.0°

  • h = −18 → 13

  • k = −14 → 10

  • l = −11 → 11

Refinement
  • Refinement on F2

  • R[F2 > 2σ(F2)] = 0.043

  • wR(F2) = 0.079

  • S = 0.99

  • 3024 reflections

  • 143 parameters

  • H atoms treated by a mixture of independent and constrained refinement

  • w = 1/[σ2(Fo2) + (0.0248P)2] where P = (Fo2 + 2Fc2)/3

  • (Δ/σ)max = 0.001

  • Δρmax = 0.39 e Å−3

  • Δρmin = −0.47 e Å−3

Table 1
Selected geometric parameters (Å, °)

Ga1—Cl3 2.1647 (10)
Ga1—Cl2 2.1652 (11)
Ga1—Cl1 2.1758 (11)
Ga1—Cl4 2.1803 (10)
N1—C7 1.304 (5)
N2—C7 1.317 (5)
C1—C7 1.475 (5)
Cl3—Ga1—Cl2 114.40 (4)
Cl3—Ga1—Cl1 107.62 (5)
Cl2—Ga1—Cl1 109.78 (4)
Cl3—Ga1—Cl4 106.56 (4)
Cl2—Ga1—Cl4 108.21 (5)
Cl1—Ga1—Cl4 110.20 (4)
C7—C1—C2—C3 −179.7 (3)
C6—C1—C7—N1 140.2 (4)
C2—C1—C7—N2 141.0 (4)

Table 2
Hydrogen-bonding geometry (Å, °)

D—H⋯A D—H H⋯A DA D—H⋯A
N1—H1A⋯Cl1 0.82 (3) 2.52 (3) 3.321 (4) 164 (4)
N1—H1B⋯Cl4i 0.83 (3) 2.53 (3) 3.343 (4) 165 (3)
N2—H2A⋯Cl2i 0.85 (3) 2.85 (3) 3.578 (4) 145 (3)
N2—H2B⋯Cl3ii 0.85 (2) 2.67 (3) 3.470 (4) 157 (3)
Symmetry codes: (i) [-x,y-{\script{1\over 2}},{\script{3\over 2}}-z]; (ii) x,y-1,z.

C-bound H atoms were placed in calculated positions (C—H = 0.95 Å) and refined using a riding model; those attached to the N atoms were located in an electron-density map and restrained in pairs to give equal N—H distances (0.82–0.85 Å). H atoms were given isotropic displacement parameters equal to 1.2 (or 1.5 for methyl H atoms) times Ueq of their parent atoms.

Data collection: SMART (Siemens, 1994[Siemens (1994). SMART and SHELXTL/PC (Version 5.0). Siemens Analytical X-ray Instruments Inc., Madison, Wisconsin, USA.]); cell refinement: SAINT (Siemens, 1995[Siemens (1995). SAINT. Version 4.021. Siemens Analytical X-ray Instruments Inc., Madison, Wisconsin, USA.]); data reduction: SAINT; program(s) used to solve structure: SHELXTL/PC (Siemens, 1994[Siemens (1994). SMART and SHELXTL/PC (Version 5.0). Siemens Analytical X-ray Instruments Inc., Madison, Wisconsin, USA.]); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997[Sheldrick, G. M. (1997). SHELXL97. University of Göttingen, Germany.]); molecular graphics: SHELXTL/PC; software used to prepare material for publication: SHELXL97.

Supporting information


Computing details top

Data collection: SMART (Siemens, 1994); cell refinement: SAINT (Siemens, 1995); data reduction: SAINT; program(s) used to solve structure: SHELXTL/PC (Siemens, 1994); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL/PC; software used to prepare material for publication: SHELXL97.

benzamidinium tetrachlogallate(III) top
Crystal data top
(C7H9N2)[GaCl4]F(000) = 656
Mr = 332.68Dx = 1.692 Mg m3
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybcCell parameters from 3209 reflections
a = 13.986 (2) Åθ = 2.4–28.0°
b = 10.8228 (19) ŵ = 2.89 mm1
c = 9.0976 (16) ÅT = 180 K
β = 108.474 (4)°Needle, white
V = 1306.1 (4) Å30.38 × 0.06 × 0.06 mm
Z = 4
Data collection top
Siemens SMART CCD area-detector
diffractometer
3024 independent reflections
Radiation source: normal-focus sealed tube1892 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.050
Detector resolution: 8.192 pixels mm-1θmax = 28.0°, θmin = 2.4°
ω scansh = 1813
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)
k = 1410
Tmin = 0.406, Tmax = 0.846l = 1111
7620 measured reflections
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.043Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.079H atoms treated by a mixture of independent and constrained refinement
S = 0.99 w = 1/[σ2(Fo2) + (0.0248P)2]
where P = (Fo2 + 2Fc2)/3
3024 reflections(Δ/σ)max = 0.001
143 parametersΔρmax = 0.39 e Å3
2 restraintsΔρmin = 0.47 e Å3
Special details top

Experimental. The temperature of the crystal was controlled using the Oxford Cryosystems Cryostream Cooler (Cosier & Glazer, 1986). Data were collected over a hemisphere of reciprocal space, by a combination of three sets of exposures. Each set had a different φ angle for the crystal and each exposure of 10 s covered 0.3° in ω. The crystal-to-detector distance was 5.01 cm. Coverage of the unique set was over 96% complete to at least 28° in θ. Crystal decay was monitored by repeating the initial frames at the end of the data collection and analyzing the duplicate reflections.

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
Ga10.16826 (3)0.92057 (4)0.74486 (5)0.03015 (13)
Cl10.27698 (8)0.79163 (9)0.89026 (12)0.0506 (3)
Cl20.05578 (8)0.82047 (9)0.56531 (12)0.0469 (3)
Cl30.25131 (8)1.05637 (9)0.65941 (12)0.0451 (3)
Cl40.09184 (8)1.02105 (9)0.88292 (11)0.0417 (3)
N10.1590 (3)0.5256 (4)0.7733 (4)0.0410 (9)
H1B0.097 (2)0.533 (3)0.749 (4)0.038 (12)*
H1A0.193 (3)0.589 (3)0.788 (4)0.046 (14)*
N20.1424 (3)0.3159 (3)0.7645 (5)0.0474 (10)
H2B0.170 (2)0.246 (3)0.767 (4)0.024 (10)*
H2A0.081 (2)0.321 (3)0.760 (4)0.043 (13)*
C10.3071 (3)0.4024 (3)0.8015 (4)0.0300 (9)
C20.3551 (3)0.4837 (4)0.7281 (4)0.0425 (10)
H20.31790.54780.66360.051*
C30.4564 (4)0.4703 (4)0.7497 (5)0.0559 (13)
H30.48890.52490.69900.067*
C40.5110 (3)0.3789 (4)0.8439 (5)0.0516 (12)
H40.58100.37050.85840.062*
C50.4642 (3)0.2993 (3)0.9174 (5)0.0429 (11)
H50.50230.23650.98340.051*
C60.3628 (3)0.3101 (3)0.8961 (4)0.0348 (9)
H60.33080.25420.94620.042*
C70.1984 (3)0.4158 (4)0.7784 (4)0.0333 (9)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Ga10.0253 (2)0.0264 (2)0.0385 (2)0.00007 (19)0.00972 (18)0.00214 (19)
Cl10.0382 (7)0.0343 (6)0.0656 (7)0.0094 (5)0.0031 (5)0.0015 (5)
Cl20.0371 (7)0.0455 (6)0.0522 (6)0.0094 (5)0.0057 (5)0.0122 (5)
Cl30.0476 (7)0.0414 (6)0.0549 (6)0.0122 (5)0.0283 (6)0.0066 (5)
Cl40.0376 (7)0.0505 (6)0.0407 (6)0.0084 (5)0.0177 (5)0.0020 (5)
N10.032 (3)0.030 (2)0.054 (2)0.0052 (19)0.004 (2)0.0029 (17)
N20.027 (2)0.032 (2)0.082 (3)0.0022 (18)0.015 (2)0.0070 (19)
C10.025 (2)0.032 (2)0.031 (2)0.0011 (17)0.0061 (17)0.0052 (17)
C20.040 (3)0.040 (2)0.046 (2)0.002 (2)0.011 (2)0.0042 (19)
C30.051 (3)0.057 (3)0.067 (3)0.009 (2)0.029 (3)0.008 (3)
C40.024 (3)0.060 (3)0.070 (3)0.001 (2)0.014 (2)0.004 (2)
C50.035 (3)0.035 (2)0.053 (3)0.0066 (19)0.006 (2)0.0002 (19)
C60.030 (2)0.029 (2)0.044 (2)0.0012 (17)0.010 (2)0.0005 (18)
C70.032 (2)0.033 (2)0.032 (2)0.0011 (19)0.0070 (18)0.0035 (18)
Geometric parameters (Å, º) top
Ga1—Cl32.1647 (10)C1—C21.398 (5)
Ga1—Cl22.1652 (11)C1—C71.475 (5)
Ga1—Cl12.1758 (11)C2—C31.375 (5)
Ga1—Cl42.1803 (10)C2—H20.9500
N1—C71.304 (5)C3—C41.372 (6)
N1—H1B0.83 (3)C3—H30.9500
N1—H1A0.82 (3)C4—C51.377 (5)
N2—C71.317 (5)C4—H40.9500
N2—H2B0.85 (2)C5—C61.375 (5)
N2—H2A0.85 (3)C5—H50.9500
C1—C61.386 (5)C6—H60.9500
Cl3—Ga1—Cl2114.40 (4)C1—C2—H2120.2
Cl3—Ga1—Cl1107.62 (5)C4—C3—C2120.6 (4)
Cl2—Ga1—Cl1109.78 (4)C4—C3—H3119.7
Cl3—Ga1—Cl4106.56 (4)C2—C3—H3119.7
Cl2—Ga1—Cl4108.21 (5)C3—C4—C5119.9 (4)
Cl1—Ga1—Cl4110.20 (4)C3—C4—H4120.0
C7—N1—H1B120 (3)C5—C4—H4120.0
C7—N1—H1A122 (3)C6—C5—C4120.4 (4)
H1B—N1—H1A118 (4)C6—C5—H5119.8
C7—N2—H2B118 (2)C4—C5—H5119.8
C7—N2—H2A121 (3)C5—C6—C1120.0 (4)
H2B—N2—H2A121 (3)C5—C6—H6120.0
C6—C1—C2119.4 (4)C1—C6—H6120.0
C6—C1—C7120.6 (3)N1—C7—N2120.9 (4)
C2—C1—C7120.0 (3)N1—C7—C1119.9 (4)
C3—C2—C1119.6 (4)N2—C7—C1119.2 (4)
C3—C2—H2120.2
C6—C1—C2—C30.5 (6)C2—C1—C6—C50.2 (5)
C7—C1—C2—C3179.7 (3)C7—C1—C6—C5179.5 (3)
C1—C2—C3—C40.7 (6)C6—C1—C7—N1140.2 (4)
C2—C3—C4—C50.2 (7)C2—C1—C7—N139.6 (5)
C3—C4—C5—C60.6 (6)C6—C1—C7—N239.3 (5)
C4—C5—C6—C10.8 (6)C2—C1—C7—N2141.0 (4)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1A···Cl10.82 (3)2.52 (3)3.321 (4)164 (4)
N1—H1B···Cl4i0.83 (3)2.53 (3)3.343 (4)165 (3)
N2—H2A···Cl2i0.85 (3)2.85 (3)3.578 (4)145 (3)
N2—H2B···Cl3ii0.85 (2)2.67 (3)3.470 (4)157 (3)
Symmetry codes: (i) x, y1/2, z+3/2; (ii) x, y1, z.
 

Acknowledgements

We acknowledge the use of the EPSRC's Chemical Database Service at Daresbury Laboratory (Fletcher et al., 1996[Fletcher, D. A., McMeeking, R. F. & Parkin, D. (1996). J. Chem. Inf. Comput. Sci. 36, 746-749.]) for access to the Cambridge Structural Database (Allen, 2002).

References

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