Guanidinium tetra­bromidomercurate(II)

Abstract

The Hg atoms in the crystal structure of the title compound, (CH₆N₃)₂[HgBr₄], are tetra­hedrally coordinated by four Br atoms and the resulting [HgBr₄]²⁻ tetra­hedral ions are linked to the [C(NH₂)₃]⁺ ions by bromine–hydrogen bonds, forming a three-dimensional network. In the structure, the anions are located on special positions. The two different Hg⋯Br distances of 2.664 (1) and 2.559 (1) Å observed in the tetra­bromidomercurate unit are due to the connection of Br atoms to different number of H atoms.

Related literature

For the ability of the guanidinium ion to make hydrogen bonds and its unique planar shape, see: Terao et al. (2000 ▶). For related literature, see: Ishihara et al. (2002 ▶); Furukawa et al. (2005 ▶)

Experimental

Crystal data

• (CH₆N₃)₂[HgBr₄]

• M _r = 640.41

• Monoclinic,

• a = 10.035 (2) Å

• b = 11.164 (2) Å

• c = 13.358 (3) Å

• β = 111.67 (3)°

• V = 1390.7 (6) ų

• Z = 4

• Mo Kα radiation

• μ = 22.53 mm⁻¹

• T = 298 K

• 0.09 × 0.09 × 0.09 mm

Data collection

• Stoe IPDS-I diffractometer

• Absorption correction: none

• 9651 measured reflections

• 1361 independent reflections

• 982 reflections with I > 2σ(I)

• R _int = 0.093

Refinement

• R[F ² > 2σ(F ²)] = 0.030

• wR(F ²) = 0.069

• S = 0.90

• 1361 reflections

• 79 parameters

• 6 restraints

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

• Δρ_max = 0.71 e Å⁻³

• Δρ_min = −1.03 e Å⁻³

Data collection: EXPOSE (Stoe & Cie, 1999 ▶); cell refinement: CELL (Stoe & Cie, 1999 ▶); data reduction: XPREP (Bruker, 2003 ▶); program(s) used to solve structure: SHELXS86 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL93 (Sheldrick, 2008 ▶); molecular graphics: DIAMOND (Crystal Impact, 2008 ▶); software used to prepare material for publication: SHELXL93 (Sheldrick, 2008 ▶).

Supplementary Material

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—H1A⋯Br2i	0.87 (9)	3.03 (4)	3.845 (8)	158 (9)
N1—H1B⋯Br1ii	0.87 (9)	2.77 (6)	3.512 (7)	144 (8)
N2—H2A⋯Br1iii	0.87 (9)	2.72 (4)	3.541 (7)	159 (8)
N2—H2B⋯Br2i	0.87 (9)	2.74 (4)	3.535 (7)	153 (8)
N3—H3A⋯Br1iv	0.87 (9)	3.05 (10)	3.505 (8)	115 (8)
N3—H3B⋯Br1iii	0.87 (9)	2.98 (8)	3.667 (9)	137 (9)

Symmetry codes: (i) ; (ii) ; (iii) ; (iv) .

supplementary crystallographic information

Comment

The guanidium ion, [C(NH₂)₃]⁺ is interesting due to its ability of making hydrogen bonds and its unique planar shape (Terao et al., 2000). Further, the guanidium ions tend to undergo reorientation motions about their (pseudo) C₃ axes in the crystals. Due to the soft nature of the Hg atom amenable to polarization, the Hg-halogen bonds are sensitive to the intermolecular interactions such as hydrogen bonding (Ishihara et al., 2002). This was evident in the halogen NQR of the Hg compounds in which the resonance lines are widely spread in frequency (Furukawa et al., 2005). Thus we are interested in studying the structure and bonding in this class of compounds. As a part of our study, we report herein the crystal structure of Guanidinium tetrabromidomercurate(II). In the structure, mercury atoms are tetrahedrally coordinated by four bromine atoms and the resulting HgBr₄ tetrahedra are interconnected to the [C(NH₂)₃]⁺ ions by bromine-hydrogen bonds (Fig. 1) forming a three-dimensional network. In the tetrabromidomercurate unit, two different Hg—Br distances were observed: Hg—Br1 = 2.664 (1) Å and Hg—Br2 = 2.559 (1) Å. The shorter distance of the latter is due to its connection with two hydrogen atoms, whereas the Br1 is connected to four different hydrogen atoms, which elongate the Hg—Br bond (Fig.2). The C(NH₂)₃ moity (Fig. 3) itself is planar where the N—H bonds are somewhat elongated (1.01 (2) Å) to form the network bonds to the bromine atoms of the HgBr₄ tetrahedra.

Experimental

Guanidinium tetrabromidomercurate(II) was prepared by slow concentration of methanolic solution containing mercuric bromide (0.01 mole) and guanidium bromide (0.02 mole) in 1:2 molar ratio. The purity of the compound was checked by elemental analysis and characterized by its NMR and NQR spectra (Furukawa et al., 2005). The single crystals used in X-ray diffraction studies were grown in methanolic solution by a slow evaporation at room temperature.

Refinement

The N-H distances were restrained to 0.87 (1)Å and the coordinates of the H atoms were refined with isotropic displacement parameters set to 1.2 times of the U_eq of the parent atom.

Figures

Fig. 1.

Molecular structure of (I), showing the atom labeling scheme. The displacement ellipsoids are drawn at the 50% probability level. The H atoms are represented as small spheres of arbitrary radii.

Fig. 2.

: Connection scheme of the HgBr42- tetrahedra with the [C(NH2)3]+ ions.

Fig. 3.

: The planar [C(NH2)3]+ ion.

Crystal data

(CH6N3)2[HgBr4]	F(000) = 1144
Mr = 640.41	Dx = 3.059 Mg m−3
Monoclinic, C2/c	Melting point: not measured K
Hall symbol: -C 2yc	Mo Kα radiation, λ = 0.71073 Å
a = 10.035 (2) Å	Cell parameters from 2000 reflections
b = 11.164 (2) Å	θ = 2.9–26.1°
c = 13.358 (3) Å	µ = 22.53 mm−1
β = 111.67 (3)°	T = 298 K
V = 1390.7 (6) Å3	Cylindric, colourless transparent
Z = 4	0.09 × 0.09 × 0.09 mm

Data collection

Stoe IPDS-I diffractometer	982 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.093
graphite	θmax = 26.1°, θmin = 2.9°
imaging plate dynamic profile intergration scans	h = −12→12
9651 measured reflections	k = −13→13
1361 independent reflections	l = −16→16

Refinement

Refinement on F2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.030	H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.069	w = 1/[σ2(Fo2) + (0.0376P)2] where P = (Fo2 + 2Fc2)/3
S = 0.90	(Δ/σ)max = 0.001
1361 reflections	Δρmax = 0.71 e Å−3
79 parameters	Δρmin = −1.03 e Å−3
6 restraints	Extinction correction: SHELXL93 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.00077 (10)

Special details

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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
Hg1	0.5000	0.71191 (4)	0.2500	0.0577 (2)
Br1	0.30789 (8)	0.86270 (7)	0.27353 (7)	0.0555 (2)
Br2	0.38905 (10)	0.60032 (7)	0.07086 (6)	0.0635 (3)
C1	0.4454 (8)	0.8215 (6)	0.6018 (6)	0.0492 (18)
N1	0.5515 (10)	0.8736 (7)	0.5829 (6)	0.070 (2)
H1A	0.592 (10)	0.818 (7)	0.558 (8)	0.084*
H1B	0.549 (10)	0.950 (2)	0.594 (8)	0.084*
N2	0.4254 (7)	0.7072 (6)	0.5904 (6)	0.0625 (17)
H2A	0.363 (7)	0.673 (8)	0.612 (7)	0.075*
H2B	0.485 (8)	0.665 (7)	0.571 (7)	0.075*
N3	0.3560 (9)	0.8857 (7)	0.6335 (7)	0.075 (2)
H3A	0.369 (11)	0.960 (3)	0.622 (8)	0.090*
H3B	0.278 (7)	0.856 (9)	0.636 (9)	0.090*

Atomic displacement parameters (Ų)

	U11	U22	U33	U12	U13	U23
Hg1	0.0706 (3)	0.0544 (3)	0.0586 (3)	0.000	0.0359 (2)	0.000
Br1	0.0569 (4)	0.0485 (4)	0.0714 (5)	−0.0003 (3)	0.0359 (4)	−0.0070 (4)
Br2	0.0950 (6)	0.0453 (5)	0.0638 (5)	−0.0062 (4)	0.0454 (5)	−0.0100 (4)
C1	0.051 (4)	0.043 (4)	0.043 (4)	0.005 (3)	0.005 (3)	−0.006 (3)
N1	0.090 (5)	0.054 (4)	0.064 (5)	−0.021 (4)	0.026 (4)	−0.001 (4)
N2	0.058 (4)	0.052 (4)	0.081 (5)	−0.005 (3)	0.030 (4)	−0.011 (4)
N3	0.081 (5)	0.063 (5)	0.073 (5)	0.011 (5)	0.018 (5)	−0.009 (4)

Geometric parameters (Å, °)

Hg1—Br2	2.5593 (10)	N1—H1A	0.87 (9)
Hg1—Br2i	2.5593 (10)	N1—H1B	0.87 (9)
Hg1—Br1	2.6639 (9)	N2—H2A	0.87 (9)
Hg1—Br1i	2.6639 (9)	N2—H2B	0.87 (9)
C1—N2	1.293 (10)	N3—H3A	0.87 (9)
C1—N1	1.316 (11)	N3—H3B	0.87 (9)
C1—N3	1.334 (11)
Br2—Hg1—Br2i	121.74 (4)	C1—N1—H1A	107 (7)
Br2—Hg1—Br1	109.51 (4)	C1—N1—H1B	109 (7)
Br2i—Hg1—Br1	106.33 (3)	H1A—N1—H1B	144 (10)
Br2—Hg1—Br1i	106.33 (3)	C1—N2—H2A	120 (6)
Br2i—Hg1—Br1i	109.51 (4)	C1—N2—H2B	118 (7)
Br1—Hg1—Br1i	101.62 (4)	H2A—N2—H2B	121 (9)
N2—C1—N1	121.0 (8)	C1—N3—H3A	107 (8)
N2—C1—N3	118.3 (8)	C1—N3—H3B	122 (8)
N1—C1—N3	120.7 (7)	H3A—N3—H3B	125 (10)

Symmetry codes: (i) −x+1, y, −z+1/2.

Hydrogen-bond geometry (Å, °)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···Br2i	0.87 (9)	3.03 (4)	3.845 (8)	158 (9)
N1—H1B···Br1ii	0.87 (9)	2.77 (6)	3.512 (7)	144 (8)
N2—H2A···Br1iii	0.87 (9)	2.72 (4)	3.541 (7)	159 (8)
N2—H2B···Br2i	0.87 (9)	2.74 (4)	3.535 (7)	153 (8)
N3—H3A···Br1iv	0.87 (9)	3.05 (10)	3.505 (8)	115 (8)
N3—H3B···Br1iii	0.87 (9)	2.98 (8)	3.667 (9)	137 (9)

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