Bis(2-methyl-4-nitro­anilinium) tetra­chloridomercurate(II)

The title compound, (C₇H₉N₂O₂)₂[HgCl₄], self-assembles into cationic organic bilayers containing the 2-methyl-4-nitro­anilinium cations, sandwiched between anionic inorganic layers built up by the distorted tetra­hedral [HgCl₄]²⁻ groups. The organic sheets are inter­linked through weak C—H...O hydrogen bonds, while they inter­act with the anionic part via strong charge-assisted N⁺—H...Cl—Hg hydrogen bonds. The [HgCl₄]²⁻ anions are bis­ected by a mirror plane passing through the metal and two of the chloride ions.

Key indicators

• Single-crystal X-ray study
• T = 173 K
• Mean [sigma](C-C) = 0.010 Å
• R factor = 0.053
• wR factor = 0.152
• Data-to-parameter ratio = 24.6

checkCIF/PLATON results

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Alert level C
PLAT342_ALERT_3_C Low Bond Precision on C-C Bonds (x 1000) Ang ...         10
PLAT432_ALERT_2_C Short Inter X...Y Contact  O1     ..  C3      ..       2.93 Ang.

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

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   1 ALERT type 2 Indicator that the structure model may be wrong or deficient
   1 ALERT type 3 Indicator that the structure quality may be low
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S1. Comment

As part of a study focused on the fundamental understanding of the non-covalent interactions occurring in organic-inorganic hybrids, the structure of bis(2-methyl-4-nitroanilinium) tetrachloromercurate, 2(C₇H₉N₂O₂)⁺.(HgCl₄)^2-, (I), was determined. It was found that the title compound is isostructural to the previously reported hybrid, bis(2-methyl-4-nitroanilinium) tetrachlorocadmate (Azumi et al., 1996). The structures of the bromide and iodide salts of the 2-methyl-4-nitroanilinium cation have already been reported (Lemmerer & Billing, 2006).

The molecular geometry and atomic numbering scheme of (I) are illustrated in Fig. 1. The asymmetric unit contains one 2-methyl-4-nitroanilinium cation and a HgCl₄^2- anion, halved by a mirror plane (x, 1/2-y, z) passing through the metal and two of the chlorine ions. The structure consists of alternating, non-interdigitated organic bilayers containing the 2-methyl-4-nitroanilium cations, and inorganic layers containing the isolated (HgCl₄)^2- anions (Fig. 2.).

In the organic bilayers the nitro groups pack in the centre of the layer, in a tail-to-tail arrangement, and the aromatic ring plane (C1->C6) forms an angle of 86.3° to the inorganic layer plane. It has been reported by Sharma and Desiraju (1994) that weak C—H···O interactions, with the nitro group as a hydrogen bond acceptor occurs in many unsaturated compounds, despite the fact that the nitro group is not very basic, and it is precisely this type of interaction the one which links both organic layers in (I): atom C3 on the aromatic ring at symmetry position (1/2 - x, 1/2 + y, z - 1/2) acts as proton donor while the O1 of nitro group at symmetry position (x, 1/2 - y, z) acts as acceptor, with an H···O distance of 2.52 Å.

The organic and inorganic layers are linked through charge assisted N⁺—H···Cl—Hg hydrogen bonds, with the hydrogen bonding interactions listed in Table 1. N1 is the only hydrogen bond donor with all three hydrogen atoms involved in hydrogen bonding. Atom H6 is shared by two chlorine atoms (Cl2 at symmetry position: (x, y, z) and Cl3 at symmetry position: (x - 1/2, 1/2 - y, 1/2 - z)) and thus forms a bifurcated interaction. Two approximately linear hydrogen bonds are formed through atoms H4 and H5 with Cl1 at symmetry positions (x - 1, y, z) and (x - 1/2, y, 1/2 - z), respectively. All four chloro ligands on the HgCl₄^2- anion act as hydrogen bond acceptors.

Related literature

The structures of bis(2-methyl-4-nitroanilinium) tetrachlorocadmate (Azumi et al., 1996) as well as those of the bromide and iodide salts of 2-methyl-4-nitroanilinium (Lemmerer & Billing, 2006) have already been reported. For related literature on C—H···O_nitro interactions, see: Sharma & Desiraju (1994).

S2. Experimental

Compound (I) was prepared by the addition of 0.097 g (0.357 mmol) of HgCl₂ (Aldrich) and 0.102 g (0.333 mmol) of 2-methyl-4-nitroaniline (Aldrich) to 6 ml of 33% HCl. Complete dissolution was obtained after refluxing at 90°C for 12 h in an oil bath. Slow cooling in oil bath over 48 h produced the crystals. A colourless crystal of 0.42 x 1/4x 0.16 mm was used for X-ray data collection.

S3. Refinement

H atoms were placed geometrically and refined in idealized positions in the riding-model approximation, with C—H 0.95 (ArH) and 0.98 Å (CH₃) and N—H = 0.91 Å; U_iso(H) = 1.5U_eq(N), 1.5U_eq(C) for methyl H atoms and 1.2U_eq(C) for other H atoms. The highest residual peaks in the final ΔF syntheses lie at 0.90 Å from Cl3.

Computing details

Data collection: SMART (Bruker, 1998); cell refinement: SAINT-Plus (Bruker, 1999); data reduction: SAINT-Plus (Bruker, 1999); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2006) and Mercury (Bruno et al., 2002); software used to prepare material for publication: WinGX (Farrugia, 1999) and PLATON (Spek, 2003).

Figures

	Fig. 1. Atom labelling scheme of (I) with thermal ellipsoids drawn at the 50% probability level. The Cl atom marked with a prime (') is at symmetry position (1/2 + x, 1/2 - y, 1/2 - z).
	Fig. 2. Packing arrangement viewed down the c-axis.

Bis(2-methyl-4-nitroanilinium) tetrachloridomercurate(II)

Crystal data

(C7H9N2O2)2[HgCl4]	Dx = 2.092 Mg m^−3
Mr = 648.71	Melting point: 441 K
Orthorhombic, Pnma	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2n	Cell parameters from 937 reflections
a = 8.2527 (11) Å	θ = 3.2–28.3°
b = 30.059 (4) Å	µ = 8.02 mm^−1
c = 8.3038 (10) Å	T = 173 K
V = 2059.9 (5) Å^3	Plate, colourless
Z = 4	0.42 × 0.25 × 0.16 mm
F(000) = 1240

Data collection

Bruker SMART CCD area-detector diffractometer	3174 independent reflections
Radiation source: fine-focus sealed tube	2197 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.091
ω scans	θmax = 32.2°, θmin = 1.4°
Absorption correction: integration (XPREP; Bruker, 1999)	h = −11→12
Tmin = 0.609, Tmax = 0.757	k = −38→44
10307 measured reflections	l = −8→11

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)] = 0.053	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.152	H-atom parameters constrained
S = 1.09	w = 1/[σ^2(Fo^2) + (0.077P)^2 + 1.1955P] where P = (Fo^2 + 2Fc^2)/3
3174 reflections	(Δ/σ)max = 0.003
129 parameters	Δρmax = 1.05 e Å^−3
0 restraints	Δρmin = −2.89 e Å^−3

Special details

Experimental. Numerical integration absorption corrections based on indexed crystal faces were applied using the XPREP routine (Bruker, 2004)

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	0.60393 (5)	0.2500	0.46538 (6)	0.02730 (16)
Cl3	0.4637 (3)	0.2500	0.1888 (3)	0.0232 (5)
Cl1	0.6690 (2)	0.17293 (6)	0.5175 (2)	0.0198 (3)
C1	0.1288 (8)	0.1395 (2)	0.5286 (9)	0.0167 (13)
C6	0.2495 (9)	0.1443 (3)	0.4129 (9)	0.0210 (15)
H3	0.2794	0.1731	0.3760	0.025*
O1	0.4612 (9)	0.0300 (2)	0.2467 (9)	0.0504 (19)
O2	0.3238 (8)	−0.00979 (19)	0.4124 (8)	0.0394 (15)
N1	0.0546 (7)	0.1794 (2)	0.5922 (8)	0.0194 (12)
H6	0.0891	0.2034	0.5347	0.029*
H5	0.0832	0.1828	0.6973	0.029*
H4	−0.0551	0.1772	0.5845	0.029*
C2	0.0779 (7)	0.0982 (2)	0.5872 (8)	0.0151 (13)
N2	0.3592 (7)	0.0258 (2)	0.3538 (8)	0.0252 (14)
C4	0.2790 (8)	0.0663 (3)	0.4125 (8)	0.0189 (14)
C3	0.1558 (8)	0.0608 (2)	0.5265 (8)	0.0171 (13)
H1	0.1257	0.0319	0.5619	0.021*
C5	0.3261 (8)	0.1068 (2)	0.3516 (8)	0.0199 (14)
H2	0.4075	0.1091	0.2711	0.024*
C7	−0.0544 (9)	0.0924 (2)	0.7085 (9)	0.0223 (16)
H9	−0.0626	0.0610	0.7383	0.033*
H8	−0.1575	0.1023	0.6621	0.033*
H7	−0.0299	0.1102	0.8045	0.033*
Cl2	0.3444 (3)	0.2500	0.6670 (3)	0.0199 (5)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Hg1	0.0319 (2)	0.0206 (2)	0.0293 (3)	0.000	0.00001 (19)	0.000
Cl3	0.0272 (13)	0.0262 (13)	0.0162 (11)	0.000	−0.0057 (10)	0.000
Cl1	0.0186 (8)	0.0166 (8)	0.0243 (8)	0.0002 (6)	−0.0007 (7)	0.0008 (7)
C1	0.018 (3)	0.016 (3)	0.017 (3)	0.000 (3)	−0.003 (3)	−0.002 (3)
C6	0.022 (3)	0.024 (4)	0.017 (3)	−0.006 (3)	0.000 (3)	−0.001 (3)
O1	0.057 (4)	0.039 (4)	0.055 (4)	−0.007 (4)	0.038 (4)	−0.013 (3)
O2	0.047 (4)	0.020 (3)	0.051 (4)	0.005 (3)	0.012 (3)	−0.007 (3)
N1	0.010 (2)	0.018 (3)	0.030 (3)	−0.001 (2)	−0.003 (2)	0.000 (3)
C2	0.010 (3)	0.023 (4)	0.013 (3)	0.000 (2)	−0.003 (2)	0.001 (3)
N2	0.020 (3)	0.027 (4)	0.030 (4)	0.000 (3)	0.004 (2)	−0.007 (3)
C4	0.019 (3)	0.025 (4)	0.013 (3)	−0.003 (3)	0.001 (3)	−0.004 (3)
C3	0.015 (3)	0.019 (3)	0.017 (3)	−0.004 (3)	−0.003 (3)	−0.002 (3)
C5	0.018 (3)	0.024 (4)	0.018 (3)	−0.004 (3)	0.005 (3)	−0.001 (3)
C7	0.021 (3)	0.022 (4)	0.024 (4)	0.001 (3)	0.010 (3)	0.003 (3)
Cl2	0.0143 (10)	0.0189 (11)	0.0266 (13)	0.000	0.0004 (9)	0.000

Geometric parameters (Å, º)

Hg1—Cl1	2.4170 (18)	N1—H5	0.9100
Hg1—Cl1^i	2.4170 (18)	N1—H4	0.9100
Hg1—Cl3	2.572 (2)	C2—C3	1.390 (10)
Hg1—Cl2	2.718 (2)	C2—C7	1.496 (10)
C1—C6	1.392 (10)	N2—C4	1.469 (10)
C1—C2	1.396 (10)	C4—C5	1.375 (10)
C1—N1	1.447 (9)	C4—C3	1.399 (10)
C6—C5	1.388 (10)	C3—H1	0.9500
C6—H3	0.9500	C5—H2	0.9500
O1—N2	1.230 (9)	C7—H9	0.9800
O2—N2	1.212 (9)	C7—H8	0.9800
N1—H6	0.9100	C7—H7	0.9800
Cl1—Hg1—Cl1^i	146.85 (9)	C1—C2—C7	123.9 (6)
Cl1—Hg1—Cl3	105.06 (4)	O2—N2—O1	123.0 (7)
Cl1^i—Hg1—Cl3	105.06 (4)	O2—N2—C4	119.3 (6)
Cl1—Hg1—Cl2	93.71 (5)	O1—N2—C4	117.6 (7)
Cl1^i—Hg1—Cl2	93.71 (5)	C5—C4—C3	124.0 (7)
Cl3—Hg1—Cl2	101.28 (8)	C5—C4—N2	119.0 (6)
C6—C1—C2	123.2 (7)	C3—C4—N2	117.0 (6)
C6—C1—N1	117.9 (6)	C2—C3—C4	119.0 (7)
C2—C1—N1	118.9 (6)	C2—C3—H1	120.5
C5—C6—C1	119.7 (7)	C4—C3—H1	120.5
C5—C6—H3	120.2	C4—C5—C6	117.1 (6)
C1—C6—H3	120.2	C4—C5—H2	121.5
C1—N1—H6	109.5	C6—C5—H2	121.5
C1—N1—H5	109.5	C2—C7—H9	109.5
H6—N1—H5	109.5	C2—C7—H8	109.5
C1—N1—H4	109.5	H9—C7—H8	109.5
H6—N1—H4	109.5	C2—C7—H7	109.5
H5—N1—H4	109.5	H9—C7—H7	109.5
C3—C2—C1	117.0 (6)	H8—C7—H7	109.5
C3—C2—C7	119.1 (7)
C2—C1—C6—C5	−0.6 (11)	O1—N2—C4—C3	175.8 (7)
N1—C1—C6—C5	178.6 (6)	C1—C2—C3—C4	0.2 (9)
C6—C1—C2—C3	1.0 (10)	C7—C2—C3—C4	179.7 (7)
N1—C1—C2—C3	−178.1 (6)	C5—C4—C3—C2	−2.1 (11)
C6—C1—C2—C7	−178.4 (7)	N2—C4—C3—C2	179.1 (6)
N1—C1—C2—C7	2.4 (10)	C3—C4—C5—C6	2.5 (11)
O2—N2—C4—C5	176.5 (7)	N2—C4—C5—C6	−178.7 (6)
O1—N2—C4—C5	−3.1 (10)	C1—C6—C5—C4	−1.2 (10)
O2—N2—C4—C3	−4.6 (10)

Symmetry code: (i) x, −y+1/2, z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H6···Cl2	0.91	2.76	3.257 (6)	116
N1—H4···Cl1^ii	0.91	2.35	3.248 (6)	170
N1—H5···Cl1^iii	0.91	2.49	3.381 (7)	167
N1—H6···Cl3^iv	0.91	2.54	3.241 (7)	134
C3—H1···O1^v	0.95	2.52	3.424 (10)	160

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