1,1'-(Ethane-1,2-di­yl)dipyridinium dibromidodichloridomercurate(II)

The Hg atom in the title compound, (C₁₂H₁₄N₂)[HgBr₂Cl₂], is coordinated by four halogen atoms in a tetra­hedral geometry. The cation lies on a centre of inversion and the anion about a mirror plane. The two halogen atoms on the mirror plane are disordered between Br and Cl in ratios of 0.921 (4):0.079 (4) and 0.795 (4):0.205 (4). The halogen atom in the general position is disordered between Br and Cl in a ratio of 0.142 (1):0.858 (1).

Key indicators

• Single-crystal X-ray study
• T = 298 K
• Mean [sigma](C-C) = 0.009 Å
• Disorder in main residue
• R factor = 0.034
• wR factor = 0.102
• Data-to-parameter ratio = 17.1

checkCIF/PLATON results

No syntax errors found



Alert level B
PLAT432_ALERT_2_B Short Inter X...Y Contact  Br1    ..  C5      ..       3.21 Ang.

Alert level C
PLAT042_ALERT_1_C Calc. and Rep. MoietyFormula Strings Differ ....          ?
PLAT062_ALERT_4_C Rescale T(min) & T(max) by .....................       0.74
PLAT241_ALERT_2_C Check High      Ueq as Compared to Neighbors for         C1
PLAT242_ALERT_2_C Check Low       Ueq as Compared to Neighbors for        Hg1
PLAT301_ALERT_3_C Main Residue  Disorder .........................      17.00 Perc.
PLAT342_ALERT_3_C Low Bond Precision on C-C Bonds (x 1000) Ang ...          9

Alert level G
ABSTM02_ALERT_3_G  When printed, the submitted absorption T values will be
            replaced by the scaled T values. Since the ratio of scaled T's
            is identical to the ratio of reported T values, the scaling
            does not imply a change to the absorption corrections used in
            the study.
            Ratio of Tmax expected/reported      0.739
            Tmax scaled      0.250 Tmin scaled      0.124
PLAT860_ALERT_3_G Note: Number of Least-Squares Restraints .......         57

   0 ALERT level A = In general: serious problem
   1 ALERT level B = Potentially serious problem
   6 ALERT level C = Check and explain
   2 ALERT level G = General alerts; check

   1 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   3 ALERT type 2 Indicator that the structure model may be wrong or deficient
   4 ALERT type 3 Indicator that the structure quality may be low
   1 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

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S1. Comment

The discrete tetrahedral tetrahalogenomercurate(II) dianion is characterized in a number of salts (Allen, 2002; CSD Version 5.28); examples of the ammonium salts include, for example, bis(tetramethylammonium) tetrachloromercurate (Amami et al., 2002), bis(tetramethylammonium) tetrabromomercurate (Kamenar & Nagl, 1976) and bis(tetramethylammonium) tetraiodomercurate (Pakhomov et al., 1991; Pickardt et al., 2006). The mercury atom in [C₁₂H₁₄N₂][HgBr₂Cl₂] is coordinated by four halogen atoms in a tetrahedral geometry; the halogen atoms are disordered (Fig. 1). Selected bond distances are given in Table 1.

Related literature

For ammonium salts of tetrahalogenomercurates(II), see: Allen (2002); Amami et al. (2002); Kamenar & Nagl (1976); Pakhomov et al. (1991); Pickardt et al. (2006). For the synthesis of the organic component, see: Xiao et al. (2006).

S2. Experimental

The salt was synthesized from the reaction of ethane-1,2-dipyridinium dibromide (0.035 g, 0.1 mmol) in methanol (5 ml) and mercuric chloride (0.054 g, 0.2 mmol) in DMF (10 ml). The mixture was set aside for the formation of colorless needle-shaped crystals in 40% yield after several days. A needle was cut to give a columnar specimen. The organic reactant was synthesized by using a literature method (Xiao et al., 2006).

S3. Refinement

Of the three halogens in the asymmetric unit, one lies in a general position and the other two on a mirror plane. Initial attempts to refine the structure with either three chlorines or three bromines gave unacceptably high R-indices and large peaks/deep holes. The three halogen atoms were then refined as three (Br+Cl) mixtures; one attempt allowed the mixtures to have the same displacement parameters as well as sharing the same site. Another attempt had the components having the same displacement parameters only. The second led to a formulation consisting of approximately two Br and two Cl atoms. The use of a restraint that fixed the number of Br and Cl atoms as exactly two each led to occupancies of 0.142 (1), 0.921 (4) and 0.795 (4), respectively, for Br1, Br2 and Br3, and 0.858 (1), 0.079 (4) and 0.205 (4), respectively, for Cl1, Cl2 and Cl3. The formulation is in fair agreement with CH&N elemental analysis.

Disorder also affected the cation; the pyridyl ring was refined as a rigid hexagon (C—C = C—N = 1.39 Å). The C(sp^3)—C(sp3) distance was restrained to 1.50 (1) Å, and the N···C(sp³) distance to 2.45 (1) Å. The displacement parameters of atoms of the cation were restrained to be nearly isotropic. C-bound H atoms were positioned geometrically (C–H = 0.93 and 0.97 Å), and were included in the refinement in the riding model approximation, with U_iso(H) = 1.2U_eq(C).

The final difference Fourier map had a large peak at 0.89 Å from N1, indicating a possible disorder in the cation. But no suitable disorder model was found for the cation.

Computing details

Data collection: SMART (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: X-SEED (Barbour, 2001); software used to prepare material for publication: publCIF (Westrip, 2007).

Figures

Fig. 1. The molecular structure of [C12H14N2][HgBr2Cl2], with displacement ellipsoids drawn at the 50% probability level. The bromine and chlorine atoms are disordered; the figures depicts the anion as an [HgX4]^2- species. The halogen atom in the general position is labelled X1 (and the symmetry-related X1^i); those in the special position are labelled X2 and X3. Hydrogen atoms are drawn as spheres of arbitrary radius. [Symmetry code (i): x, 3/2 – y, z.]. Unlabelled atoms in the cation are related to the labelled ones by the symmetry code (1 – x, 1 – y, 1 – z).

1,1'-(Ethane-1,2-diyl)dipyridinium dibromidodichloridomercurate(II)

Crystal data

(C12H14N2)[HgBr2Cl2]	F(000) = 1136
Mr = 617.56	Dx = 2.382 Mg m^−3
Orthorhombic, Pnma	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2n	Cell parameters from 2764 reflections
a = 17.952 (1) Å	θ = 2.3–22.7°
b = 14.381 (1) Å	µ = 13.88 mm^−1
c = 6.6707 (5) Å	T = 298 K
V = 1722.1 (2) Å^3	Column, colourless
Z = 4	0.20 × 0.10 × 0.10 mm

Data collection

Bruker APEX area-detector diffractometer	1573 independent reflections
Radiation source: fine-focus sealed tube	1395 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.038
φ and ω scans	θmax = 25.0°, θmin = 2.3°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −21→20
Tmin = 0.168, Tmax = 0.338	k = −16→17
9021 measured reflections	l = −7→7

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.034	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.102	H-atom parameters constrained
S = 1.05	w = 1/[σ^2(Fo^2) + (0.0654P)^2 + 2.4853P] where P = (Fo^2 + 2Fc^2)/3
1572 reflections	(Δ/σ)max = 0.001
92 parameters	Δρmax = 1.40 e Å^−3
57 restraints	Δρmin = −1.17 e Å^−3

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
Hg1	0.92942 (2)	0.7500	0.65028 (6)	0.0427 (2)
Br1	0.913 (4)	0.606 (5)	0.471 (9)	0.058 (2)	0.142 (1)
Cl1	0.9142 (14)	0.6012 (19)	0.441 (3)	0.058 (2)	0.858 (1)
Br2	0.8251 (2)	0.7500	0.9091 (3)	0.0849 (8)	0.921 (4)
Cl2	0.821 (8)	0.7500	0.853 (14)	0.0849 (8)	0.079 (4)
Br3	1.06769 (13)	0.7500	0.7582 (4)	0.0631 (7)	0.795 (4)
Cl3	1.0543 (16)	0.7500	0.818 (5)	0.0631 (7)	0.205 (4)
N1	0.59356 (19)	0.5290 (3)	0.4047 (7)	0.066 (2)
C1	0.6519 (3)	0.5275 (4)	0.5418 (6)	0.078 (3)
H1	0.6479	0.4924	0.6583	0.094*
C2	0.7161 (2)	0.5786 (4)	0.5046 (7)	0.057 (2)
H2	0.7551	0.5776	0.5963	0.068*
C3	0.7221 (2)	0.6311 (4)	0.3304 (7)	0.059 (2)
H3	0.7651	0.6653	0.3056	0.071*
C4	0.6638 (3)	0.6325 (4)	0.1933 (6)	0.055 (2)
H4	0.6678	0.6677	0.0768	0.067*
C5	0.5995 (2)	0.5815 (4)	0.2305 (7)	0.064 (2)
H5	0.5605	0.5824	0.1388	0.077*
C6	0.5273 (3)	0.4739 (4)	0.4394 (11)	0.075 (3)
H6A	0.5407	0.4170	0.5085	0.090*
H6B	0.5050	0.4572	0.3118	0.090*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Hg1	0.0363 (3)	0.0426 (3)	0.0491 (3)	0.000	0.00310 (16)	0.000
Br1	0.0424 (11)	0.064 (3)	0.067 (7)	−0.0014 (15)	−0.001 (4)	−0.031 (4)
Cl1	0.0424 (11)	0.064 (3)	0.067 (7)	−0.0014 (15)	−0.001 (4)	−0.031 (4)
Br2	0.0753 (12)	0.1119 (13)	0.0676 (17)	0.000	0.0385 (16)	0.000
Cl2	0.0753 (12)	0.1119 (13)	0.0676 (17)	0.000	0.0385 (16)	0.000
Br3	0.0350 (12)	0.0791 (11)	0.0751 (19)	0.000	−0.0030 (9)	0.000
Cl3	0.0350 (12)	0.0791 (11)	0.0751 (19)	0.000	−0.0030 (9)	0.000
N1	0.031 (3)	0.096 (5)	0.072 (4)	−0.011 (4)	−0.002 (3)	0.031 (4)
C1	0.057 (5)	0.104 (6)	0.075 (6)	−0.010 (5)	−0.009 (4)	0.033 (5)
C2	0.025 (4)	0.069 (5)	0.076 (5)	−0.003 (3)	−0.008 (3)	0.017 (4)
C3	0.041 (4)	0.066 (5)	0.070 (5)	−0.009 (4)	0.004 (4)	0.016 (4)
C4	0.049 (5)	0.054 (4)	0.063 (4)	−0.015 (4)	0.004 (4)	0.010 (4)
C5	0.047 (4)	0.075 (5)	0.070 (5)	−0.011 (4)	0.004 (4)	0.022 (4)
C6	0.087 (6)	0.066 (5)	0.073 (5)	0.018 (5)	−0.008 (5)	−0.008 (4)

Geometric parameters (Å, º)

Hg1—Cl2	2.37 (11)	C1—H1	0.93
Hg1—Br1	2.41 (5)	C2—C3	1.39
Hg1—Br1^i	2.41 (5)	C2—H2	0.93
Hg1—Cl3	2.50 (3)	C3—C4	1.39
Hg1—Br2	2.548 (3)	C3—H3	0.93
Hg1—Cl1^i	2.571 (19)	C4—C5	1.39
Hg1—Cl1	2.571 (19)	C4—H4	0.93
Hg1—Br3	2.584 (3)	C5—H5	0.93
N1—C1	1.39	C6—C6^ii	1.476 (6)
N1—C5	1.39	C6—H6A	0.97
N1—C6	1.448 (6)	C6—H6B	0.97
C1—C2	1.39
Cl2—Hg1—Br1^i	101 (2)	C1—N1—C5	120.0
Cl2—Hg1—Br1	101 (2)	C1—N1—C6	120.4 (4)
Br1^i—Hg1—Br1	119 (4)	C5—N1—C6	119.6 (4)
Cl2—Hg1—Cl3	119 (3)	N1—C1—C2	120.0
Br1^i—Hg1—Cl3	109.1 (17)	N1—C1—H1	120.0
Br1—Hg1—Cl3	109.1 (17)	C2—C1—H1	120.0
Br1^i—Hg1—Br2	104.4 (16)	C3—C2—C1	120.0
Br1—Hg1—Br2	104.4 (16)	C3—C2—H2	120.0
Cl3—Hg1—Br2	110.9 (6)	C1—C2—H2	120.0
Cl2—Hg1—Cl1^i	103.0 (16)	C4—C3—C2	120.0
Br1—Hg1—Cl1^i	115.7 (11)	C4—C3—H3	120.0
Cl3—Hg1—Cl1^i	109.7 (7)	C2—C3—H3	120.0
Br2—Hg1—Cl1^i	106.9 (6)	C3—C4—C5	120.0
Cl2—Hg1—Cl1	103.0 (16)	C3—C4—H4	120.0
Br1^i—Hg1—Cl1	115.7 (11)	C5—C4—H4	120.0
Cl3—Hg1—Cl1	109.7 (6)	C4—C5—N1	120.0
Br2—Hg1—Cl1	106.9 (6)	C4—C5—H5	120.0
Cl1^i—Hg1—Cl1	112.7 (13)	N1—C5—H5	120.0
Cl2—Hg1—Br3	129 (3)	N1—C6—C6^ii	110.8 (6)
Br1^i—Hg1—Br3	104.6 (16)	N1—C6—H6A	109.5
Br1—Hg1—Br3	104.6 (16)	C6^ii—C6—H6A	109.5
Br2—Hg1—Br3	121.16 (9)	N1—C6—H6B	109.5
Cl1^i—Hg1—Br3	104.7 (6)	C6^ii—C6—H6B	109.5
Cl1—Hg1—Br3	104.7 (6)	H6A—C6—H6B	108.1
C6—N1—C1—C2	178.2 (3)	C1—N1—C6—C6^ii	87.7 (9)
C6—N1—C5—C4	−178.2 (3)	C5—N1—C6—C6^ii	−94.1 (9)

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