1,1'-(p-Phenyl­enedimethyl­ene)dipyridinium trichloridoiodidomercurate(II)

The Hg atom in the title compound, (C₁₈H₁₈N₂)[HgCl_2.75I_1.25], is coordinated by four halogen atoms in a tetra­hedral geometry. Two of the four halogen atoms are each disordered between I and Cl, with the I:Cl ratios being 0.5793 (15):0.4208 (15) and 0.6708 (15):0.3292 (15). The two independent cations lie on different inversion centres.

Key indicators

• Single-crystal X-ray study
• T = 295 K
• Mean [sigma](C-C) = 0.013 Å
• Disorder in main residue
• R factor = 0.042
• wR factor = 0.113
• Data-to-parameter ratio = 16.9

checkCIF/PLATON results

No syntax errors found



Alert level A
ABSTM02_ALERT_3_A  The ratio of expected to reported Tmax/Tmin(RR') is < 0.50
            Tmin and Tmax reported:      0.089     0.400
            Tmin(prime) and Tmax expected:      0.147     0.330
            RR(prime) =      0.499
            Please check that your absorption correction is appropriate.

Author Response: The range is given in the SADABS run, for which a model with heavy atoms was assumed. The transmission range is in agreement with the presence o heavy atoms.

PLAT061_ALERT_3_A Tmax/Tmin Range Test RR' too Large .............       0.43

Author Response: As above.

Alert level B
PLAT213_ALERT_2_B Atom Cl1     has ADP max/min Ratio .............       4.70 oblat
PLAT242_ALERT_2_B Check Low       Ueq as Compared to Neighbors for         N2

Alert level C
PLAT041_ALERT_1_C Calc. and Rep. SumFormula Strings    Differ ....          ?
PLAT042_ALERT_1_C Calc. and Rep. MoietyFormula Strings Differ ....          ?
PLAT045_ALERT_1_C Calculated and Reported Z Differ by ............       0.25 Ratio
PLAT062_ALERT_4_C Rescale T(min) & T(max) by .....................       0.82
PLAT241_ALERT_2_C Check High      Ueq as Compared to Neighbors for        C10
PLAT241_ALERT_2_C Check High      Ueq as Compared to Neighbors for        C13
PLAT241_ALERT_2_C Check High      Ueq as Compared to Neighbors for        C15
PLAT250_ALERT_2_C Large U3/U1 Ratio for Average U(i,j) Tensor ....       2.07
PLAT301_ALERT_3_C Main Residue  Disorder .........................       4.00 Perc.
PLAT342_ALERT_3_C Low Bond Precision on C-C Bonds (x 1000) Ang ...         13
PLAT790_ALERT_4_C Centre of Gravity not Within Unit Cell: Resd.  #          2
              C18 H18 N2

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      0.824
            Tmax scaled      0.330 Tmin scaled      0.073

Author Response: The range is given in the SADABS run, for which a model with heavy atoms was assumed. The transmission range is in agreement with the presence o heavy atoms.

PLAT860_ALERT_3_G Note: Number of Least-Squares Restraints .......          4

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

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

---

S1. Comment

The preceding study reports the structure of a tetrahedral dibromodichloromercurate(II), which was isolated as a 1,2-ethanedipyridinium salt (Wang et al., 2007). Replacing the cation by α,α'-4-xylyldipyridinium furnishes a similar tetrahalomercurate. The anion of the salt is of composed 2.75 chlorines and 1.25 iodines (Fig. 1); the metal atom shows tetrahedral coordination. Selected bond distances are given in Table 1.

Related literature

For related literature of tetrahalogenomercurates, see: Wang et al. (2007). For the synthesis of the organic component, see: Sindelar et al. (2004).

S2. Experimental

The salt was synthesized from the reaction of α,α'-4-xylyldipyridinium dichloride (0.033 g, 0.1 mmol) in methanol (5 ml) and mercuric iodide (0.091 g, 0.2 mmol) in DMF (10 ml). The mixture was set aside for the formation of colorless crystals in 30% yield after several days. The organic reactant was synthesized by using a literature method (Sindelar et al., 2004).

S3. Refinement

The four halogens lie in general positions. Initial attempts to refine the structure with either four iodines or four chlorines gave unacceptably high R-indices and large peaks/holes. The four halogen atoms were then refined as four (I+Cl) mixtures, with same displacement parameters. This led to a formulation consisting of approximately 1.25 I and 2.75 Cl atoms. The use of a restraint that fixed the number of I and Cl atoms as exactly 1.25 I and 2.75 Cl led to the occupancy of I1 as 0.6 and that of I2 as 0.7; the occupancies of I3 and I4 were nearly zero. As such, the Cl3 and Cl4 atoms were each assigned full occupancy, so that only the I1/Cl1 and I2/Cl2 halogen atoms were disordered.

The anion is [HgCl_2.75I_1.25]^2-, but because it has nearly integral numbers of chlorine and iodine atoms, it is regarded as [HgCl₃I] for the purpose of naming the compound. The formulation is, however, in poor agreement with CH&N elemental analysis, so that the synthesis probably yielded a range of tetrahalogenmercurates. Other formulations led to somewhat larger peaks/deep holes.

The disorder affected the cation; the pyridyl ring was refined as a rigid hexagon (C—C = C—N = 1.39 Å). C-bound H atoms were generated geometrically (C–H 0.93 Å), and were included in the refinement in the riding-model approximation, with U(H) set to 1.2U_eq(C).

The final difference Fourier map had a large peak at 0.91 Å from Hg1, but was otherwise featureless.

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 [C18H18N2][HgCl2.75I1.25]. Displacement ellipsoids are drawn at the 50% probability level. Labels X1 and X2 denote the disordered I and Cl atoms (I1, I2, Cl1 and Cl2). Hydrogen atoms are drawn as spheres of arbitrary radius. [Symmetry code (i): 1 - x, 1 - y, 2 - z; (ii) 2 - x, -1 - y, 2 - z.]

1,1'-(p-Phenylenedimethylene)dipyridinium trichloridoiodidomercurate(II)

Crystal data

(C18H18N2)[HgCl2.75I1.25]	F(000) = 1332
Mr = 719.05	Dx = 2.210 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 4098 reflections
a = 14.2901 (9) Å	θ = 2.5–22.8°
b = 9.4764 (6) Å	µ = 9.25 mm^−1
c = 16.151 (1) Å	T = 295 K
β = 98.785 (1)°	Block, colourless
V = 2161.5 (2) Å^3	0.20 × 0.15 × 0.12 mm
Z = 4

Data collection

Bruker APEX area-detector diffractometer	3792 independent reflections
Radiation source: fine-focus sealed tube	3097 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.037
φ and ω scans	θmax = 25.0°, θmin = 1.4°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −16→16
Tmin = 0.089, Tmax = 0.400	k = −11→11
15087 measured reflections	l = −19→19

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)] = 0.042	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.113	H-atom parameters constrained
S = 1.05	w = 1/[σ^2(Fo^2) + (0.0609P)^2 + 2.8764P] where P = (Fo^2 + 2Fc^2)/3
3792 reflections	(Δ/σ)max = 0.001
224 parameters	Δρmax = 1.10 e Å^−3
4 restraints	Δρmin = −0.57 e Å^−3

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Hg1	0.74880 (2)	0.42222 (4)	0.68910 (2)	0.06253 (16)
I1	0.8501 (3)	0.1938 (3)	0.6478 (3)	0.0731 (6)	0.5793 (15)
Cl1	0.8430 (17)	0.2326 (13)	0.6529 (17)	0.077 (4)	0.4208 (15)
I2	0.6700 (2)	0.3885 (4)	0.83326 (16)	0.0613 (5)	0.6708 (15)
Cl2	0.6851 (19)	0.386 (3)	0.8131 (13)	0.058 (4)	0.3292 (15)
Cl3	0.62488 (15)	0.4902 (2)	0.56647 (12)	0.0617 (5)
Cl4	0.84520 (15)	0.6549 (2)	0.69693 (14)	0.0646 (5)
N1	0.3671 (4)	0.3819 (5)	0.7986 (2)	0.0523 (16)
C1	0.4004 (4)	0.2569 (4)	0.7687 (3)	0.063 (2)
H1	0.4048	0.1761	0.8017	0.075*
C2	0.4271 (4)	0.2529 (5)	0.6895 (3)	0.071 (2)
H2	0.4494	0.1693	0.6695	0.085*
C3	0.4205 (5)	0.3738 (6)	0.6402 (2)	0.071 (3)
H3	0.4384	0.3711	0.5873	0.085*
C4	0.3871 (5)	0.4987 (5)	0.6701 (3)	0.078 (3)
H4	0.3827	0.5796	0.6372	0.094*
C5	0.3604 (4)	0.5028 (4)	0.7493 (3)	0.069 (2)
H5	0.3381	0.5863	0.7693	0.082*
C6	0.3432 (7)	0.3870 (9)	0.8825 (5)	0.065 (2)
H6A	0.3274	0.2928	0.8994	0.078*
H6B	0.2879	0.4464	0.8827	0.078*
C7	0.4251 (6)	0.4449 (8)	0.9450 (4)	0.054 (2)
C8	0.4980 (7)	0.3591 (8)	0.9794 (5)	0.060 (2)
H8	0.4966	0.2638	0.9655	0.072*
C9	0.4264 (7)	0.5878 (9)	0.9654 (5)	0.063 (2)
H9	0.3772	0.6468	0.9424	0.076*
N2	0.8607 (4)	−0.1805 (4)	0.9319 (4)	0.0560 (16)
C10	0.8258 (5)	−0.0683 (7)	0.9734 (4)	0.100 (4)
H10	0.7900	−0.0854	1.0159	0.120*
C11	0.8443 (7)	0.0696 (5)	0.9515 (5)	0.113 (5)
H11	0.8209	0.1447	0.9792	0.136*
C12	0.8977 (6)	0.0953 (5)	0.8880 (6)	0.104 (4)
H12	0.9101	0.1875	0.8733	0.125*
C13	0.9327 (6)	−0.0170 (7)	0.8465 (5)	0.119 (5)
H13	0.9684	0.0002	0.8040	0.143*
C14	0.9142 (5)	−0.1549 (6)	0.8685 (4)	0.093 (3)
H14	0.9375	−0.2300	0.8407	0.111*
C15	0.8358 (7)	−0.3242 (10)	0.9509 (8)	0.092 (3)
H15A	0.7977	−0.3652	0.9019	0.110*
H15B	0.7980	−0.3230	0.9959	0.110*
C16	0.9223 (7)	−0.4144 (8)	0.9763 (7)	0.067 (3)
C17	0.9533 (8)	−0.5048 (10)	0.9197 (7)	0.078 (3)
H17	0.9219	−0.5087	0.8649	0.094*
C18	0.9696 (8)	−0.4109 (9)	1.0562 (7)	0.074 (3)
H18	0.9491	−0.3501	1.0949	0.089*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Hg1	0.0675 (3)	0.0560 (2)	0.0639 (2)	0.00375 (15)	0.00949 (17)	0.00970 (15)
I1	0.0721 (11)	0.0430 (16)	0.1092 (11)	0.0162 (12)	0.0297 (8)	0.0095 (15)
Cl1	0.092 (6)	0.017 (5)	0.129 (8)	0.030 (4)	0.041 (5)	0.017 (5)
I2	0.0767 (13)	0.0561 (7)	0.0568 (13)	−0.0089 (8)	0.0283 (9)	0.0031 (9)
Cl2	0.087 (9)	0.049 (5)	0.050 (8)	−0.001 (5)	0.050 (5)	0.002 (5)
Cl3	0.0677 (13)	0.0627 (12)	0.0528 (11)	0.0040 (10)	0.0031 (9)	0.0056 (9)
Cl4	0.0588 (13)	0.0624 (12)	0.0726 (13)	−0.0014 (10)	0.0106 (10)	0.0147 (10)
N1	0.070 (5)	0.047 (3)	0.043 (3)	−0.010 (3)	0.017 (3)	−0.007 (3)
C1	0.074 (6)	0.067 (5)	0.049 (4)	−0.007 (4)	0.013 (4)	0.002 (4)
C2	0.079 (6)	0.071 (6)	0.066 (6)	−0.002 (5)	0.024 (5)	−0.007 (5)
C3	0.083 (7)	0.081 (6)	0.050 (5)	−0.019 (5)	0.013 (5)	0.002 (5)
C4	0.118 (8)	0.073 (6)	0.044 (5)	−0.004 (6)	0.011 (5)	0.012 (4)
C5	0.091 (7)	0.061 (5)	0.053 (5)	0.003 (5)	0.008 (4)	−0.002 (4)
C6	0.085 (6)	0.065 (5)	0.049 (5)	−0.020 (5)	0.025 (4)	−0.006 (4)
C7	0.078 (6)	0.049 (4)	0.036 (4)	−0.014 (4)	0.018 (4)	−0.005 (3)
C8	0.098 (7)	0.041 (4)	0.044 (4)	−0.008 (5)	0.019 (4)	0.003 (3)
C9	0.083 (7)	0.056 (5)	0.053 (5)	0.004 (4)	0.015 (5)	0.002 (4)
N2	0.052 (4)	0.043 (4)	0.072 (4)	0.003 (3)	0.008 (3)	0.006 (3)
C10	0.133 (11)	0.102 (9)	0.075 (7)	0.034 (7)	0.043 (7)	0.014 (6)
C11	0.185 (15)	0.066 (7)	0.088 (8)	0.033 (8)	0.021 (9)	−0.011 (6)
C12	0.099 (9)	0.046 (6)	0.160 (13)	0.006 (5)	−0.004 (8)	0.011 (7)
C13	0.138 (12)	0.088 (8)	0.148 (12)	0.012 (8)	0.073 (10)	0.049 (8)
C14	0.124 (9)	0.058 (6)	0.109 (8)	0.010 (6)	0.057 (7)	−0.001 (6)
C15	0.068 (6)	0.060 (6)	0.150 (10)	0.003 (5)	0.022 (6)	0.031 (6)
C16	0.063 (6)	0.038 (4)	0.098 (7)	−0.013 (4)	0.010 (5)	0.018 (4)
C17	0.092 (8)	0.056 (6)	0.084 (7)	−0.008 (5)	0.006 (6)	0.008 (5)
C18	0.087 (7)	0.051 (5)	0.088 (7)	0.006 (5)	0.025 (6)	0.007 (5)

Geometric parameters (Å, º)

Hg1—Cl1	2.371 (13)	C8—H8	0.93
Hg1—Cl2	2.347 (13)	C9—C8^i	1.386 (13)
Hg1—Cl3	2.530 (2)	C9—H9	0.93
Hg1—Cl4	2.593 (2)	N2—C10	1.39
Hg1—I1	2.742 (3)	N2—C14	1.39
Hg1—I2	2.755 (2)	N2—C15	1.452 (10)
N1—C1	1.39	C10—C11	1.39
N1—C5	1.39	C10—H10	0.93
N1—C6	1.447 (8)	C11—C12	1.39
C1—C2	1.39	C11—H11	0.93
C1—H1	0.93	C12—C13	1.39
C2—C3	1.39	C12—H12	0.93
C2—H2	0.93	C13—C14	1.39
C3—C4	1.39	C13—H13	0.93
C3—H3	0.93	C14—H14	0.93
C4—C5	1.39	C15—C16	1.508 (13)
C4—H4	0.93	C15—H15A	0.97
C5—H5	0.93	C15—H15B	0.97
C6—C7	1.527 (12)	C16—C18	1.361 (15)
C6—H6A	0.97	C16—C17	1.375 (14)
C6—H6B	0.97	C17—C18^ii	1.369 (14)
C7—C8	1.371 (12)	C17—H17	0.93
C7—C9	1.393 (10)	C18—C17^ii	1.369 (14)
C8—C9^i	1.386 (13)	C18—H18	0.93
Cl2—Hg1—Cl1	114.2 (9)	C9—C7—C6	119.2 (8)
Cl2—Hg1—Cl3	112.9 (7)	C7—C8—C9^i	121.0 (8)
Cl1—Hg1—Cl3	110.8 (7)	C7—C8—H8	119.5
Cl2—Hg1—Cl4	110.7 (7)	C9^i—C8—H8	119.5
Cl1—Hg1—Cl4	109.8 (6)	C8^i—C9—C7	119.1 (8)
Cl3—Hg1—Cl4	97.16 (7)	C8^i—C9—H9	120.5
Cl2—Hg1—I1	112.4 (7)	C7—C9—H9	120.5
Cl1—Hg1—I1	2.9 (6)	C10—N2—C14	120.0
Cl3—Hg1—I1	110.05 (11)	C10—N2—C15	119.9 (6)
Cl4—Hg1—I1	112.76 (10)	C14—N2—C15	120.0 (6)
Cl2—Hg1—I2	2.0 (8)	N2—C10—C11	120.0
Cl1—Hg1—I2	116.2 (6)	N2—C10—H10	120.0
Cl3—Hg1—I2	111.32 (9)	C11—C10—H10	120.0
Cl4—Hg1—I2	109.89 (9)	C12—C11—C10	120.0
I1—Hg1—I2	114.39 (12)	C12—C11—H11	120.0
C1—N1—C5	120.0	C10—C11—H11	120.0
C1—N1—C6	119.7 (5)	C11—C12—C13	120.0
C5—N1—C6	120.2 (5)	C11—C12—H12	120.0
C2—C1—N1	120.0	C13—C12—H12	120.0
C2—C1—H1	120.0	C14—C13—C12	120.0
N1—C1—H1	120.0	C14—C13—H13	120.0
C1—C2—C3	120.0	C12—C13—H13	120.0
C1—C2—H2	120.0	C13—C14—N2	120.0
C3—C2—H2	120.0	C13—C14—H14	120.0
C4—C3—C2	120.0	N2—C14—H14	120.0
C4—C3—H3	120.0	N2—C15—C16	111.8 (7)
C2—C3—H3	120.0	N2—C15—H15A	109.3
C5—C4—C3	120.0	C16—C15—H15A	109.3
C5—C4—H4	120.0	N2—C15—H15B	109.3
C3—C4—H4	120.0	C16—C15—H15B	109.3
C4—C5—N1	120.0	H15A—C15—H15B	107.9
C4—C5—H5	120.0	C18—C16—C17	118.9 (9)
N1—C5—H5	120.0	C18—C16—C15	120.8 (10)
N1—C6—C7	111.4 (7)	C17—C16—C15	120.4 (10)
N1—C6—H6A	109.4	C18^ii—C17—C16	120.0 (10)
C7—C6—H6A	109.4	C18^ii—C17—H17	120.0
N1—C6—H6B	109.4	C16—C17—H17	120.0
C7—C6—H6B	109.4	C16—C18—C17^ii	121.1 (10)
H6A—C6—H6B	108.0	C16—C18—H18	119.4
C8—C7—C9	119.9 (8)	C17^ii—C18—H18	119.4
C8—C7—C6	120.9 (7)
C6—N1—C1—C2	−177.4 (6)	C15—N2—C10—C11	−175.7 (7)
C6—N1—C5—C4	177.4 (6)	C15—N2—C14—C13	175.6 (7)
C1—N1—C6—C7	96.1 (7)	C10—N2—C15—C16	−124.6 (8)
C5—N1—C6—C7	−81.2 (8)	C14—N2—C15—C16	59.7 (12)
N1—C6—C7—C8	−82.8 (9)	N2—C15—C16—C18	81.6 (12)
N1—C6—C7—C9	95.7 (9)	N2—C15—C16—C17	−100.2 (11)
C9—C7—C8—C9^i	−0.1 (13)	C18—C16—C17—C18^ii	0.0 (15)
C6—C7—C8—C9^i	178.4 (7)	C15—C16—C17—C18^ii	−178.3 (8)
C8—C7—C9—C8^i	0.1 (13)	C17—C16—C18—C17^ii	0.0 (15)
C6—C7—C9—C8^i	−178.4 (7)	C15—C16—C18—C17^ii	178.3 (8)

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