Benzamidinium tetra­chloro­gallate(III)

Barker, J.; Errington, W.; Wallbridge, M.G.H.

doi:10.1107/S1600536805008597

metal-organic compounds

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ISSN: 2056-9890

Volume 61| Part 4| April 2005| Pages m748-m750

https://doi.org/10.1107/S1600536805008597

Benzamidinium tetrachlorogallate(III)

James Barker,^a ^* William Errington ^b and Malcolm G. H. Wallbridge ^b

^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 ) continues, particularly with regard to antiviral and antitumour activity (Fimiani et al., 1990 ; Sharma et al., 1997 ; Kratz et al., 1992 ). This fact has directed us to extend our previous work in the area (Barker et al., 1996 ) to encompass systems containing gallium chloride and the amidinium ion. The crystal structure of the title compound, (I), 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.

The molecular structure of (I) is shown in Fig. 1 and selected geometric parameters are listed in Table 1. 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], but similar to those found in benzamidinium acetylacetonatotetracarbonylrhenate(II) (Lenhert et al., 1984 ). The C—C_amidine distances of the parent amidine [1.489 (3) Å; Barker et al., 1996] 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 ]. In the N—C—N group, a three-centre four π-electron system (Kapp et al., 1996 ), 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 ).

The GaCl₄⁻ anion is essentially tetrahedral, with Ga—Cl distances (Table 1) within the expected range; an examination of the Cambridge Structural Database (Version 5.23; Allen, 2002 ; Fletcher et al., 1996 ) shows that, for 37 structures containing the GaCl₄⁻ unit (e.g. Hausen et al., 1978 ; Jakubas et al., 1997 ), 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). 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
The asymmetric unit of (I

), 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]
M_r = 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
D_x = 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 ) T_min = 0.406, T_max = 0.846
7620 measured reflections
3024 independent reflections
1892 reflections with I > 2σ(I)
R_int = 0.050
θ_max = 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(F_o²) + (0.0248P)²] where P = (F_o² + 2F_c²)/3
(Δ/σ)_max = 0.001
Δρ_max = 0.39 e Å⁻³
Δρ_min = −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	D⋯A	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 U_eq of their parent atoms.

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.

Supporting information

Crystal structure: contains datablocks I, global. DOI: https://doi.org/10.1107/S1600536805008597/hg6154sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536805008597/hg6154Isup2.hkl

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
M_r = 332.68	D_x = 1.692 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 3209 reflections
a = 13.986 (2) Å	θ = 2.4–28.0°
b = 10.8228 (19) Å	µ = 2.89 mm⁻¹
c = 9.0976 (16) Å	T = 180 K
β = 108.474 (4)°	Needle, white
V = 1306.1 (4) Å³	0.38 × 0.06 × 0.06 mm
Z = 4

Data collection top

Siemens SMART CCD area-detector diffractometer	3024 independent reflections
Radiation source: normal-focus sealed tube	1892 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.050
Detector resolution: 8.192 pixels mm^-1	θ_max = 28.0°, θ_min = 2.4°
ω scans	h = −18→13
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	k = −14→10
T_min = 0.406, T_max = 0.846	l = −11→11
7620 measured reflections

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.043	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.079	H atoms treated by a mixture of independent and constrained refinement
S = 0.99	w = 1/[σ²(F_o²) + (0.0248P)²] where P = (F_o² + 2F_c²)/3
3024 reflections	(Δ/σ)_max = 0.001
143 parameters	Δρ_max = 0.39 e Å⁻³
2 restraints	Δρ_min = −0.47 e Å⁻³

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

	x	y	z	U_iso*/U_eq
Ga1	0.16826 (3)	0.92057 (4)	0.74486 (5)	0.03015 (13)
Cl1	0.27698 (8)	0.79163 (9)	0.89026 (12)	0.0506 (3)
Cl2	0.05578 (8)	0.82047 (9)	0.56531 (12)	0.0469 (3)
Cl3	0.25131 (8)	1.05637 (9)	0.65941 (12)	0.0451 (3)
Cl4	0.09184 (8)	1.02105 (9)	0.88292 (11)	0.0417 (3)
N1	0.1590 (3)	0.5256 (4)	0.7733 (4)	0.0410 (9)
H1B	0.097 (2)	0.533 (3)	0.749 (4)	0.038 (12)*
H1A	0.193 (3)	0.589 (3)	0.788 (4)	0.046 (14)*
N2	0.1424 (3)	0.3159 (3)	0.7645 (5)	0.0474 (10)
H2B	0.170 (2)	0.246 (3)	0.767 (4)	0.024 (10)*
H2A	0.081 (2)	0.321 (3)	0.760 (4)	0.043 (13)*
C1	0.3071 (3)	0.4024 (3)	0.8015 (4)	0.0300 (9)
C2	0.3551 (3)	0.4837 (4)	0.7281 (4)	0.0425 (10)
H2	0.3179	0.5478	0.6636	0.051*
C3	0.4564 (4)	0.4703 (4)	0.7497 (5)	0.0559 (13)
H3	0.4889	0.5249	0.6990	0.067*
C4	0.5110 (3)	0.3789 (4)	0.8439 (5)	0.0516 (12)
H4	0.5810	0.3705	0.8584	0.062*
C5	0.4642 (3)	0.2993 (3)	0.9174 (5)	0.0429 (11)
H5	0.5023	0.2365	0.9834	0.051*
C6	0.3628 (3)	0.3101 (3)	0.8961 (4)	0.0348 (9)
H6	0.3308	0.2542	0.9462	0.042*
C7	0.1984 (3)	0.4158 (4)	0.7784 (4)	0.0333 (9)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Ga1	0.0253 (2)	0.0264 (2)	0.0385 (2)	−0.00007 (19)	0.00972 (18)	−0.00214 (19)
Cl1	0.0382 (7)	0.0343 (6)	0.0656 (7)	0.0094 (5)	−0.0031 (5)	−0.0015 (5)
Cl2	0.0371 (7)	0.0455 (6)	0.0522 (6)	−0.0094 (5)	0.0057 (5)	−0.0122 (5)
Cl3	0.0476 (7)	0.0414 (6)	0.0549 (6)	−0.0122 (5)	0.0283 (6)	−0.0066 (5)
Cl4	0.0376 (7)	0.0505 (6)	0.0407 (6)	0.0084 (5)	0.0177 (5)	−0.0020 (5)
N1	0.032 (3)	0.030 (2)	0.054 (2)	0.0052 (19)	0.004 (2)	−0.0029 (17)
N2	0.027 (2)	0.032 (2)	0.082 (3)	−0.0022 (18)	0.015 (2)	−0.0070 (19)
C1	0.025 (2)	0.032 (2)	0.031 (2)	−0.0011 (17)	0.0061 (17)	−0.0052 (17)
C2	0.040 (3)	0.040 (2)	0.046 (2)	0.002 (2)	0.011 (2)	0.0042 (19)
C3	0.051 (3)	0.057 (3)	0.067 (3)	−0.009 (2)	0.029 (3)	0.008 (3)
C4	0.024 (3)	0.060 (3)	0.070 (3)	0.001 (2)	0.014 (2)	−0.004 (2)
C5	0.035 (3)	0.035 (2)	0.053 (3)	0.0066 (19)	0.006 (2)	0.0002 (19)
C6	0.030 (2)	0.029 (2)	0.044 (2)	−0.0012 (17)	0.010 (2)	0.0005 (18)
C7	0.032 (2)	0.033 (2)	0.032 (2)	−0.0011 (19)	0.0070 (18)	−0.0035 (18)

Geometric parameters (Å, º) top

Ga1—Cl3	2.1647 (10)	C1—C2	1.398 (5)
Ga1—Cl2	2.1652 (11)	C1—C7	1.475 (5)
Ga1—Cl1	2.1758 (11)	C2—C3	1.375 (5)
Ga1—Cl4	2.1803 (10)	C2—H2	0.9500
N1—C7	1.304 (5)	C3—C4	1.372 (6)
N1—H1B	0.83 (3)	C3—H3	0.9500
N1—H1A	0.82 (3)	C4—C5	1.377 (5)
N2—C7	1.317 (5)	C4—H4	0.9500
N2—H2B	0.85 (2)	C5—C6	1.375 (5)
N2—H2A	0.85 (3)	C5—H5	0.9500
C1—C6	1.386 (5)	C6—H6	0.9500

Cl3—Ga1—Cl2	114.40 (4)	C1—C2—H2	120.2
Cl3—Ga1—Cl1	107.62 (5)	C4—C3—C2	120.6 (4)
Cl2—Ga1—Cl1	109.78 (4)	C4—C3—H3	119.7
Cl3—Ga1—Cl4	106.56 (4)	C2—C3—H3	119.7
Cl2—Ga1—Cl4	108.21 (5)	C3—C4—C5	119.9 (4)
Cl1—Ga1—Cl4	110.20 (4)	C3—C4—H4	120.0
C7—N1—H1B	120 (3)	C5—C4—H4	120.0
C7—N1—H1A	122 (3)	C6—C5—C4	120.4 (4)
H1B—N1—H1A	118 (4)	C6—C5—H5	119.8
C7—N2—H2B	118 (2)	C4—C5—H5	119.8
C7—N2—H2A	121 (3)	C5—C6—C1	120.0 (4)
H2B—N2—H2A	121 (3)	C5—C6—H6	120.0
C6—C1—C2	119.4 (4)	C1—C6—H6	120.0
C6—C1—C7	120.6 (3)	N1—C7—N2	120.9 (4)
C2—C1—C7	120.0 (3)	N1—C7—C1	119.9 (4)
C3—C2—C1	119.6 (4)	N2—C7—C1	119.2 (4)
C3—C2—H2	120.2

C6—C1—C2—C3	0.5 (6)	C2—C1—C6—C5	0.2 (5)
C7—C1—C2—C3	−179.7 (3)	C7—C1—C6—C5	−179.5 (3)
C1—C2—C3—C4	−0.7 (6)	C6—C1—C7—N1	140.2 (4)
C2—C3—C4—C5	0.2 (7)	C2—C1—C7—N1	−39.6 (5)
C3—C4—C5—C6	0.6 (6)	C6—C1—C7—N2	−39.3 (5)
C4—C5—C6—C1	−0.8 (6)	C2—C1—C7—N2	141.0 (4)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	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−1/2, −z+3/2; (ii) x, y−1, z.

Acknowledgements

We acknowledge the use of the EPSRC's Chemical Database Service at Daresbury Laboratory (Fletcher et al., 1996) for access to the Cambridge Structural Database (Allen, 2002).

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