Bis­(tetraethyl­ammonium) di-μ-bromo-bis­[di­bromo­mercurate(II)], (Et₄N)₂[Hg₂Br₆]

The structure of (Et₄N)₂[Hg₂Br₆] contains dinuclear [Hg₂Br₆]²⁻ species as isolated anions. Charge balance is achieved by ordered [Et₄N]⁺ cations. An inversion centre is located at the centre of the [Hg₂Br₆]²⁻ unit.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.016 Å
• R factor = 0.034
• wR factor = 0.067
• Data-to-parameter ratio = 22.4

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level A:



DIFF_019  Alert A _diffrn_standards_number is missing
          Number of standards used in measurement.

DIFF_020  Alert A _diffrn_standards_interval_count and
          _diffrn_standards_interval_time are missing. Number of measurements
          between standards or time (min) between standards.

DIFF_022  Alert A _diffrn_standards_decay_% is missing
          Percentage decrease in standards intensity.


 3 Alert Level A = Potentially serious problem

 0 Alert Level B = Potential problem

 0 Alert Level C = Please check

---

S1. Comment

The crystal structures of several trihalogenomercurate(II) salts have been reported and show a wide variety of stereochemical arrangements, as listed in a recent overview (Serezhkin et al., 2001). Many different types of halogenomercurate(II) anions were observed, dependent on the stoichiometry, as well as on the size and charge of the cation. With the smaller [Me₄N]⁺ cation, for example, the structure consists of trigonal planar [HgBr₃]⁻ anions which are connected into infinite chains by long Hg···Cl contacts (White, 1963). The same anionic structure was found for (Et₄N)[HgCl₃] (Sandström & Liem, 1978).

The structure of (Et₄N)₂[Hg₂Br₆], (I), consists of isolated bitetrahedral [Hg₂Br₆]²⁻ units consisting of two tetrahedra sharing one common edge. Two short bonds of 2.5085 (12) and 2.5319 (13) Å, and two long bonds to the bridging bromide ions of 2.7360 (11) and 2.7618 (11) Å are observed. This type of distorted tetrahedral coordination is also found in other complexes with discrete dimeric [Hg₂X₆]²⁻ units (X = Cl, Br, I), e.g. in MgHg₃Cl₈·6H₂O (Brodersen et al., 1983), (Ph₃AsOH)₂HgBr₄ (Harris et al., 1967) and (NEt₄)[HgI₃] (Goggin et al., 1982). In (I), charge balance is achieved by ordered [Et₄N]⁺ cations, which are quite remote from the anions although there are H atoms in the range 2.7–3.1 Å from Br⁻, with Br···H—C angles in the range 160–170°. A symmetry centre is located in the middle of the [Hg₂Br₆]²⁻ units.

S2. Experimental

1 mmol (0.1717 g) of tetraethylammonium bromide, (Et₄)NBr, and 1 mmol (0.2715 g) of mercuric bromide HgBr₂, were dissolved by stirring in 50 ml me thanol at 323 K until a clear solution was obtained. Single crystals were obtained when the solution was allowed to sit at room temperature for 2 d.

Computing details

Data collection: X-AREA (Stoe & Cie, 2001); cell refinement: X-STEP32 (Stoe & Cie, 2000); data reduction: X-RED (Stoe & Cie, 2001); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Brandenburg, Bonn, 1999); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. Packing diagram of (Et4N)2[Hg2Br6], viewed down the a axis.
	Fig. 2. Bitetrahedral [Hg2Br6]^2− units sharing one common edge. Displacement ellipsoids are at the 50% probability level.
	Fig. 3. [Et4N]^+ cation. Displacement ellipsoids are at the 50% probability level.

(I)

Crystal data

(C8H20N)2[Hg2Br6]	F(000) = 1040
Mr = 1141.14	Dx = 2.492 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 10530 reflections
a = 9.1148 (16) Å	θ = 2.3–25.0°
b = 10.8302 (13) Å	µ = 17.97 mm^−1
c = 16.140 (4) Å	T = 293 K
β = 107.377 (17)°	Prism, colorless
V = 1520.5 (5) Å^3	0.2 × 0.15 × 0.1 mm
Z = 2

Data collection

Stoe Imaging Plate Diffraction System (IPDS-I) diffractometer	2665 independent reflections
Radiation source: fine-focus sealed tube	1450 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.097
ϕ scans	θmax = 25.0°, θmin = 2.3°
Absorption correction: numerical (X-SHAPE; Stoe & Cie, 1998)	h = −10→10
Tmin = 0.051, Tmax = 0.166	k = −12→12
10530 measured reflections	l = −19→18

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.034	H-atom parameters constrained
wR(F^2) = 0.067	w = 1/[σ^2(Fo^2) + (0.0161P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 0.81	(Δ/σ)max = 0.001
2665 reflections	Δρmax = 0.66 e Å^−3
119 parameters	Δρmin = −1.11 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.00203 (12)

Special details

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 (Ų)

	x	y	z	Uiso*/Ueq
Hg1	0.14441 (5)	0.37623 (4)	0.06097 (3)	0.06386 (18)
Br1	0.20423 (12)	0.36463 (12)	0.22440 (7)	0.0669 (3)
Br2	0.26762 (15)	0.23448 (10)	−0.02166 (9)	0.0802 (4)
Br3	0.16792 (10)	0.61764 (10)	0.01128 (7)	0.0567 (3)
N1	0.7227 (8)	0.4212 (6)	0.2792 (5)	0.0400 (18)
C1	0.6627 (11)	0.2912 (8)	0.2543 (7)	0.055 (3)
H1B	0.5537	0.2962	0.2239	0.066*
H1A	0.6742	0.2445	0.3071	0.066*
C2	0.8894 (10)	0.4092 (9)	0.3390 (7)	0.057 (3)
H2B	0.8904	0.3546	0.3869	0.069*
H2A	0.9516	0.3713	0.3066	0.069*
C3	0.9623 (12)	0.5320 (11)	0.3758 (8)	0.076 (3)
H3C	1.0645	0.5177	0.4133	0.091*
H3B	0.9017	0.5702	0.4082	0.091*
H3A	0.9666	0.5852	0.3290	0.091*
C4	0.6094 (13)	0.4214 (10)	0.4075 (7)	0.074 (3)
H4C	0.5439	0.4690	0.4321	0.089*
H4B	0.7097	0.4149	0.4489	0.089*
H4A	0.5667	0.3404	0.3932	0.089*
C5	0.6221 (11)	0.4847 (9)	0.3258 (7)	0.053 (3)
H5B	0.6615	0.5675	0.3412	0.064*
H5A	0.5195	0.4927	0.2855	0.064*
C6	0.7233 (11)	0.4988 (9)	0.1988 (6)	0.050 (3)
H6B	0.7579	0.5817	0.2177	0.061*
H6A	0.7969	0.4631	0.1729	0.061*
C7	0.5707 (12)	0.5068 (11)	0.1310 (7)	0.074 (3)
H7C	0.5801	0.5558	0.0833	0.089*
H7B	0.4976	0.5445	0.1554	0.089*
H7A	0.5363	0.4254	0.1108	0.089*
C8	0.7398 (16)	0.2204 (10)	0.1983 (9)	0.092 (4)
H8C	0.6942	0.1400	0.1861	0.111*
H8B	0.8474	0.2122	0.2283	0.111*
H8A	0.7267	0.2641	0.1448	0.111*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Hg1	0.0648 (3)	0.0649 (3)	0.0617 (3)	0.0066 (3)	0.0187 (2)	−0.0023 (3)
Br1	0.0596 (7)	0.0843 (8)	0.0559 (6)	−0.0066 (7)	0.0158 (5)	−0.0007 (7)
Br2	0.0885 (9)	0.0596 (7)	0.1107 (10)	−0.0028 (6)	0.0574 (8)	−0.0139 (7)
Br3	0.0488 (6)	0.0493 (5)	0.0691 (7)	−0.0079 (5)	0.0132 (5)	−0.0027 (6)
N1	0.036 (4)	0.040 (4)	0.047 (5)	0.006 (3)	0.017 (4)	0.008 (4)
C1	0.053 (7)	0.040 (5)	0.076 (8)	−0.012 (5)	0.025 (6)	−0.007 (5)
C2	0.040 (6)	0.067 (7)	0.063 (6)	0.014 (5)	0.011 (5)	0.021 (6)
C3	0.057 (7)	0.094 (9)	0.069 (9)	−0.016 (6)	0.007 (6)	0.004 (7)
C4	0.072 (8)	0.094 (9)	0.070 (8)	0.006 (6)	0.045 (6)	−0.004 (7)
C5	0.042 (6)	0.051 (6)	0.074 (8)	0.009 (5)	0.029 (5)	0.000 (6)
C6	0.057 (7)	0.052 (6)	0.049 (7)	−0.009 (5)	0.027 (6)	0.009 (5)
C7	0.066 (8)	0.091 (8)	0.053 (8)	−0.002 (7)	0.001 (6)	0.022 (6)
C8	0.122 (11)	0.057 (7)	0.115 (11)	−0.003 (7)	0.061 (10)	−0.020 (8)

Geometric parameters (Å, º)

Hg1—Br2	2.5082 (12)	C3—H3A	0.9600
Hg1—Br1	2.5322 (13)	C4—C5	1.521 (14)
Hg1—Br3^i	2.7359 (11)	C4—H4C	0.9600
Hg1—Br3	2.7618 (11)	C4—H4B	0.9600
Br3—Hg1^i	2.7359 (11)	C4—H4A	0.9600
N1—C5	1.514 (11)	C5—H5B	0.9700
N1—C1	1.521 (11)	C5—H5A	0.9700
N1—C6	1.547 (11)	C6—C7	1.493 (13)
N1—C2	1.544 (11)	C6—H6B	0.9700
C1—C8	1.509 (13)	C6—H6A	0.9700
C1—H1B	0.9700	C7—H7C	0.9600
C1—H1A	0.9700	C7—H7B	0.9600
C2—C3	1.525 (14)	C7—H7A	0.9600
C2—H2B	0.9700	C8—H8C	0.9600
C2—H2A	0.9700	C8—H8B	0.9600
C3—H3C	0.9600	C8—H8A	0.9600
C3—H3B	0.9600
Br2—Hg1—Br1	122.15 (5)	C5—C4—H4C	109.5
Br2—Hg1—Br3^i	111.24 (4)	C5—C4—H4B	109.5
Br1—Hg1—Br3^i	108.55 (4)	H4C—C4—H4B	109.5
Br2—Hg1—Br3	109.82 (4)	C5—C4—H4A	109.5
Br1—Hg1—Br3	109.77 (4)	H4C—C4—H4A	109.5
Br3^i—Hg1—Br3	90.82 (3)	H4B—C4—H4A	109.5
Hg1^i—Br3—Hg1	89.18 (3)	C4—C5—N1	116.1 (7)
C5—N1—C1	109.2 (7)	C4—C5—H5B	108.3
C5—N1—C6	108.9 (7)	N1—C5—H5B	108.3
C1—N1—C6	111.9 (7)	C4—C5—H5A	108.3
C5—N1—C2	110.9 (7)	N1—C5—H5A	108.3
C1—N1—C2	107.2 (6)	H5B—C5—H5A	107.4
C6—N1—C2	108.8 (7)	C7—C6—N1	114.2 (8)
N1—C1—C8	115.7 (8)	C7—C6—H6B	108.7
N1—C1—H1B	108.4	N1—C6—H6B	108.7
C8—C1—H1B	108.4	C7—C6—H6A	108.7
N1—C1—H1A	108.4	N1—C6—H6A	108.7
C8—C1—H1A	108.4	H6B—C6—H6A	107.6
H1B—C1—H1A	107.4	C6—C7—H7C	109.5
C3—C2—N1	113.8 (8)	C6—C7—H7B	109.5
C3—C2—H2B	108.8	H7C—C7—H7B	109.5
N1—C2—H2B	108.8	C6—C7—H7A	109.5
C3—C2—H2A	108.8	H7C—C7—H7A	109.5
N1—C2—H2A	108.8	H7B—C7—H7A	109.5
H2B—C2—H2A	107.7	C1—C8—H8C	109.5
C2—C3—H3C	109.5	C1—C8—H8B	109.5
C2—C3—H3B	109.5	H8C—C8—H8B	109.5
H3C—C3—H3B	109.5	C1—C8—H8A	109.5
C2—C3—H3A	109.5	H8C—C8—H8A	109.5
H3C—C3—H3A	109.5	H8B—C8—H8A	109.5
H3B—C3—H3A	109.5

Symmetry code: (i) −x, −y+1, −z.