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Bis(4-amino-3,5-di­chloro­pyridinium) tetra­chloridomercurate(II)

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aDepartment of Chemistry, Mother Teresa Women's University, Kodaikanal, Tamil Nadu, India, bChemistry Department, University of Fribourg, Chemin du Musée 9, CH-1700 Fribourg, Switzerland, cInstitute of Physics, University of Neuchâtel, Rue Emile-Argand 11, CH-2000 Neuchâtel, Switzerland, and dDepartment of Chemistry, Sharif University of Technology, Tehran, Iran
*Correspondence e-mail: [email protected]

Edited by W. T. A. Harrison, University of Aberdeen, United Kingdom (Received 3 December 2025; accepted 11 December 2025; online 24 December 2025)

The asymmetric unit of the title compound, (C5H5Cl2N2)2[HgCl4], comprises two 4-amino-3,5-di­chloro­pyridinium cations protonated at the pyridine N atoms and one tetra­hedral tetra­chlorido­mercurate(II) anion. The linking forces in the extended structure are predominantly N—H⋯Cl, bifurcated N—H⋯(Cl,Cl) and C—H⋯Cl hydrogen bonds, which connect the cations and anions into a three-dimensional network.

3D view (loading...)
[Scheme 3D1]
Chemical scheme
[Scheme 1]

Structure description

Following previous reports on the crystal structure of the parent 4-amino-3,5-di­chloro­pyridine (Anantheeswary et al., 2024View full citation) and our recent work on 4-amino-3,5-di­chloro­pyridinium 3-hy­droxy­picolinate monohydrate (Ashokan et al., 2023View full citation), we now describe the synthesis and structural characterization of the title salt, (C5H5Cl2N2)2[HgCl4].

The mercury(II) atom in the complex anion is coordinated by four chlorido ligands (Fig. 1[link]) in a distorted tetra­hedral shape (Table 1[link]), which is typical behaviour for a d10 soft Lewis acid. The Hg—Cl bond lengths range from 2.485 (15) to 2.491 (14) Å, while Cl—Hg—Cl angles fall in the range 103.00 (5) to 121.6 (5)°. The 4-amino-3,5-di­chloro­pyridinium cations are protonated at atoms N1 and N3 of the pyridine moiety. This protonation is evidenced by the increase in the inter­nal angle C1—N1—C5 = 121.5 (5)° and C10—N3—C6 = 121.8 (5)° compared with the corresponding angle in neutral 4-amino-5,6-di­chloro pyridine [116.4 (5)°] (Anantheeswary et al., 2024View full citation). Otherwise, the geometrical data for the title compound are in good agreement with literature data (Jellali et al., 2024View full citation). In the extended structure, the components are linked by numerous N—H⋯Cl, N—H⋯(Cl,Cl) and C—H⋯Cl (Table 2[link]) hydrogen bonds as shown in Fig. 2[link], which generates a three-dimensional network. All the chlorido ions of the complex anion accept at least one hydrogen bond.

Table 1
Selected geometric parameters (Å, °)

Hg1—Cl7 2.4771 (15) Hg1—Cl6 2.4854 (15)
Hg1—Cl8 2.4846 (15) Hg1—Cl5 2.4908 (14)
       
Cl7—Hg1—Cl8 121.61 (5) Cl7—Hg1—Cl5 105.31 (5)
Cl7—Hg1—Cl6 103.00 (5) Cl8—Hg1—Cl5 103.92 (5)
Cl8—Hg1—Cl6 104.09 (5) Cl6—Hg1—Cl5 120.16 (6)

Table 2
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A DA D—H⋯A
N1—H1N⋯Cl8 0.87 2.53 3.202 (6) 134
N1—H1N⋯Cl8i 0.87 2.54 3.190 (6) 132
N2—H2NA⋯Cl7ii 0.87 2.60 3.439 (5) 162
N2—H2NB⋯Cl7iii 0.87 2.51 3.338 (5) 159
N3—H3N⋯Cl5iv 0.87 2.78 3.387 (5) 128
N3—H3N⋯Cl6v 0.87 2.60 3.255 (6) 133
N4—H4NA⋯Cl5 0.87 2.47 3.229 (5) 146
N4—H4NB⋯Cl6vi 0.87 2.46 3.265 (6) 154
C1—H1⋯Cl8 0.94 2.81 3.356 (6) 118
C5—H5⋯Cl8i 0.94 2.75 3.308 (6) 119
C10—H10⋯Cl5iv 0.94 2.77 3.396 (6) 125
Symmetry codes: (i) Mathematical equation; (ii) Mathematical equation; (iii) Mathematical equation; (iv) Mathematical equation; (v) Mathematical equation; (vi) Mathematical equation.
[Figure 1]
Figure 1
The asymmetric unit of the title compound with 50% probability displacement ellipsoids.
[Figure 2]
Figure 2
View of the crystal packing of the title compound along the b-axis direction with the complex anions shown in polyhedral representation.

A search of the Cambridge Structural Database (Version 5.43, update November 2022; Groom et al., 2016View full citation) for related structures revealed CSD refcodes BOLCUE: bis­(3-amino-2-chloro­pyridinium)tetra­kis­(chlorido)­mercurate(II) (Mrad et al., 2024View full citation); AGEWUF: 2-2′-bi­pyridine­diium tetra­bromido­mercurate(II) (Ali et al., 2008View full citation); AJIKAG: bis­(1,3-diethyl-1H-3,1-benzimidazole-3-ium)tetra­bromido­mercurate(II) (Li et al., 2009View full citation) and AQEDUX: bis­(3-{[(pyridine-3-yl)meth­yl]amino}­pyridine-1-ium) tetra­iodido­mercurate (Ye et al., 2016View full citation).

Synthesis and crystallization

4-Amino-3,5-di­chloro­pyridine (45 mg) and mercury(II) chloride (67 mg) were used as starting materials. Each reagent was dissolved separately in methanol and water, respectively. The solutions were combined and stirred magnetically at room temperature, with the addition of 2 to 3 drops of dilute HCl to get a clear solution.. The resulting clear solution was left to stand for slow evaporation at room temperature. Colourless crystals suitable for X-ray diffraction were obtained after several days.

Refinement

Crystal data, data collection, and structure refinement details are summarized in Table 3[link].

Table 3
Experimental details

Crystal data
Chemical formula (C5H5Cl2N2)2[HgCl4]
Mr 670.41
Crystal system, space group Monoclinic, C2/c
Temperature (K) 250
a, b, c (Å) 18.0721 (6), 9.2125 (2), 23.7047 (8)
β (°) 101.652 (3)
V3) 3865.2 (2)
Z 8
Radiation type Mo Kα
μ (mm−1) 9.07
Crystal size (mm) 0.76 × 0.54 × 0.34
 
Data collection
Diffractometer STOE IPDS II
Absorption correction Multi-scan (X-RED32; Stoe, 2023View full citation)
Tmin, Tmax 0.035, 0.223
No. of measured, independent and observed [I > 2σ(I)] reflections 19023, 3877, 3645
Rint 0.041
(sin θ/λ)max−1) 0.621
 
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.034, 0.092, 1.13
No. of reflections 3877
No. of parameters 209
H-atom treatment H-atom parameters constrained
Δρmax, Δρmin (e Å−3) 1.34, −1.43
Computer programs: X-AREA WinXpose, Recipe, Integrate and LANA (Stoe, 2023View full citation), SHELXT2019/3 (Sheldrick, 2015aView full citation), SHELXL2019/3 (Sheldrick, 2015bView full citation), PLATON (Spek, 2020View full citation), Mercury (Macrae et al., 2020View full citation) and publCIF (Westrip, 2010View full citation).

Structural data


Computing details top

Bis(4-amino-3,5-dichloropyridinium) tetrachloridomercurate(II) top
Crystal data top
(C5H5Cl2N2)2[HgCl4]F(000) = 2512
Mr = 670.41Dx = 2.304 Mg m3
Monoclinic, C2/cMo Kα radiation, λ = 0.71073 Å
a = 18.0721 (6) ÅCell parameters from 25660 reflections
b = 9.2125 (2) Åθ = 1.8–26.8°
c = 23.7047 (8) ŵ = 9.07 mm1
β = 101.652 (3)°T = 250 K
V = 3865.2 (2) Å3Block, colourless
Z = 80.76 × 0.54 × 0.34 mm
Data collection top
STOE IPDS II
diffractometer
3877 independent reflections
Radiation source: sealed X-ray tube, 12 x 0.4 mm long-fine focus3645 reflections with I > 2σ(I)
Plane graphite monochromatorRint = 0.041
Detector resolution: 6.67 pixels mm-1θmax = 26.2°, θmin = 2.6°
rotation method, ω scansh = 2222
Absorption correction: multi-scan
(X-RED32; Stoe, 2023)
k = 1110
Tmin = 0.035, Tmax = 0.223l = 2929
19023 measured reflections
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.034H-atom parameters constrained
wR(F2) = 0.092 w = 1/[σ2(Fo2) + (0.0433P)2 + 32.4079P]
where P = (Fo2 + 2Fc2)/3
S = 1.13(Δ/σ)max = 0.001
3877 reflectionsΔρmax = 1.34 e Å3
209 parametersΔρmin = 1.43 e Å3
0 restraintsExtinction correction: (SHELXL-2019/3; Sheldrick, 2015b), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: dualExtinction coefficient: 0.00160 (7)
Special details top

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. All H atoms were positioned geometrically [C—H = 0.94, N—H = 0.87 Å] and were refined using a riding model with Uiso(H) = 1.2 Ueq(carrier).

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Cl10.77457 (8)0.70283 (17)0.41102 (6)0.0390 (3)
Cl20.82254 (8)0.30420 (17)0.58344 (6)0.0400 (3)
N10.6440 (3)0.5048 (6)0.4991 (2)0.0369 (11)
H1N0.5960060.5058400.4996080.044*
N20.8697 (3)0.5031 (6)0.4970 (2)0.0430 (12)
H2NA0.9003170.4485330.5210730.052*
H2NB0.8871660.5573620.4726180.052*
C10.6698 (3)0.5874 (6)0.4607 (3)0.0349 (12)
H10.6358290.6443040.4344540.042*
C20.7442 (3)0.5896 (6)0.4594 (2)0.0319 (12)
C30.7973 (3)0.5036 (6)0.4975 (2)0.0304 (11)
C40.7652 (3)0.4178 (6)0.5361 (2)0.0312 (11)
C50.6903 (3)0.4209 (7)0.5366 (2)0.0352 (12)
H50.6709540.3640340.5631850.042*
Cl30.45226 (9)0.82260 (17)0.15818 (7)0.0444 (4)
Cl40.29236 (11)0.8407 (2)0.32800 (7)0.0536 (4)
N30.3817 (3)1.1382 (6)0.2446 (2)0.0403 (11)
H3N0.3845471.2324820.2450970.048*
N40.3683 (3)0.6958 (6)0.2426 (2)0.0453 (13)
H4NA0.3443450.6510240.2657930.054*
H4NB0.3893160.6463030.2187720.054*
C60.4142 (3)1.0637 (6)0.2073 (3)0.0365 (12)
H60.4397991.1132700.1823420.044*
C70.4101 (3)0.9163 (6)0.2059 (3)0.0343 (12)
C80.3727 (3)0.8380 (6)0.2434 (2)0.0326 (11)
C90.3399 (3)0.9243 (6)0.2810 (3)0.0349 (12)
C100.3449 (4)1.0711 (6)0.2810 (3)0.0397 (13)
H100.3225991.1259590.3065760.048*
Hg10.46587 (2)0.40614 (3)0.37445 (2)0.03929 (12)
Cl50.33340 (8)0.42430 (15)0.31931 (6)0.0376 (3)
Cl60.57310 (10)0.42101 (15)0.32352 (8)0.0447 (4)
Cl70.47767 (8)0.15743 (18)0.41499 (7)0.0447 (4)
Cl80.48132 (7)0.62415 (16)0.43745 (6)0.0352 (3)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Cl10.0401 (7)0.0461 (8)0.0348 (7)0.0001 (6)0.0173 (6)0.0071 (6)
Cl20.0328 (7)0.0520 (8)0.0353 (7)0.0013 (6)0.0067 (5)0.0099 (6)
N10.023 (2)0.052 (3)0.038 (3)0.000 (2)0.0127 (19)0.003 (2)
N20.026 (2)0.062 (3)0.042 (3)0.002 (2)0.011 (2)0.015 (2)
C10.027 (3)0.042 (3)0.035 (3)0.001 (2)0.005 (2)0.004 (2)
C20.033 (3)0.039 (3)0.026 (3)0.005 (2)0.013 (2)0.001 (2)
C30.025 (2)0.041 (3)0.028 (2)0.002 (2)0.011 (2)0.005 (2)
C40.029 (3)0.039 (3)0.026 (3)0.001 (2)0.007 (2)0.002 (2)
C50.029 (3)0.049 (3)0.030 (3)0.003 (2)0.013 (2)0.006 (2)
Cl30.0522 (9)0.0443 (8)0.0431 (8)0.0036 (7)0.0250 (7)0.0067 (6)
Cl40.0700 (11)0.0523 (9)0.0481 (9)0.0009 (8)0.0345 (8)0.0042 (7)
N30.048 (3)0.028 (2)0.045 (3)0.003 (2)0.010 (2)0.002 (2)
N40.060 (3)0.036 (3)0.048 (3)0.001 (2)0.029 (3)0.002 (2)
C60.037 (3)0.035 (3)0.037 (3)0.002 (2)0.006 (2)0.001 (2)
C70.038 (3)0.034 (3)0.032 (3)0.001 (2)0.010 (2)0.001 (2)
C80.037 (3)0.034 (3)0.027 (3)0.002 (2)0.007 (2)0.000 (2)
C90.037 (3)0.037 (3)0.032 (3)0.001 (2)0.011 (2)0.001 (2)
C100.048 (3)0.034 (3)0.039 (3)0.005 (3)0.012 (3)0.004 (2)
Hg10.03396 (16)0.04079 (17)0.04560 (17)0.00137 (9)0.01388 (10)0.00097 (9)
Cl50.0353 (7)0.0351 (7)0.0416 (7)0.0016 (5)0.0060 (6)0.0068 (6)
Cl60.0570 (9)0.0323 (7)0.0555 (9)0.0049 (6)0.0370 (8)0.0050 (6)
Cl70.0339 (7)0.0474 (8)0.0567 (9)0.0056 (6)0.0182 (6)0.0199 (7)
Cl80.0288 (6)0.0424 (7)0.0378 (7)0.0016 (5)0.0152 (5)0.0010 (6)
Geometric parameters (Å, º) top
Cl1—C21.719 (5)N3—C101.342 (8)
Cl2—C41.720 (6)N3—C61.344 (8)
N1—C51.337 (8)N3—H3N0.8700
N1—C11.340 (8)N4—C81.312 (8)
N1—H1N0.8700N4—H4NA0.8700
N2—C31.312 (7)N4—H4NB0.8700
N2—H2NA0.8700C6—C71.360 (8)
N2—H2NB0.8700C6—H60.9400
C1—C21.353 (8)C7—C81.418 (8)
C1—H10.9400C8—C91.411 (8)
C2—C31.418 (8)C9—C101.355 (8)
C3—C41.418 (8)C10—H100.9400
C4—C51.357 (8)Hg1—Cl72.4771 (15)
C5—H50.9400Hg1—Cl82.4846 (15)
Cl3—C71.719 (6)Hg1—Cl62.4854 (15)
Cl4—C91.720 (6)Hg1—Cl52.4908 (14)
C5—N1—C1121.5 (5)C8—N4—H4NA120.0
C5—N1—H1N119.2C8—N4—H4NB120.0
C1—N1—H1N119.2H4NA—N4—H4NB120.0
C3—N2—H2NA120.0N3—C6—C7119.8 (6)
C3—N2—H2NB120.0N3—C6—H6120.1
H2NA—N2—H2NB120.0C7—C6—H6120.1
N1—C1—C2120.6 (5)C6—C7—C8121.6 (6)
N1—C1—H1119.7C6—C7—Cl3119.2 (5)
C2—C1—H1119.7C8—C7—Cl3119.2 (4)
C1—C2—C3121.6 (5)N4—C8—C9122.7 (5)
C1—C2—Cl1118.5 (5)N4—C8—C7122.2 (5)
C3—C2—Cl1119.9 (4)C9—C8—C7115.0 (5)
N2—C3—C4122.8 (5)C10—C9—C8121.8 (6)
N2—C3—C2122.9 (5)C10—C9—Cl4119.2 (5)
C4—C3—C2114.3 (5)C8—C9—Cl4119.0 (4)
C5—C4—C3122.1 (5)N3—C10—C9120.1 (6)
C5—C4—Cl2118.5 (4)N3—C10—H10120.0
C3—C4—Cl2119.4 (4)C9—C10—H10120.0
N1—C5—C4119.9 (5)Cl7—Hg1—Cl8121.61 (5)
N1—C5—H5120.1Cl7—Hg1—Cl6103.00 (5)
C4—C5—H5120.1Cl8—Hg1—Cl6104.09 (5)
C10—N3—C6121.8 (5)Cl7—Hg1—Cl5105.31 (5)
C10—N3—H3N119.1Cl8—Hg1—Cl5103.92 (5)
C6—N3—H3N119.1Cl6—Hg1—Cl5120.16 (6)
C5—N1—C1—C20.9 (9)C10—N3—C6—C70.2 (9)
N1—C1—C2—C31.1 (9)N3—C6—C7—C80.8 (9)
N1—C1—C2—Cl1177.6 (5)N3—C6—C7—Cl3179.8 (5)
C1—C2—C3—N2179.7 (6)C6—C7—C8—N4180.0 (6)
Cl1—C2—C3—N21.6 (8)Cl3—C7—C8—N40.9 (8)
C1—C2—C3—C40.1 (8)C6—C7—C8—C91.0 (8)
Cl1—C2—C3—C4178.5 (4)Cl3—C7—C8—C9180.0 (4)
N2—C3—C4—C5179.2 (6)N4—C8—C9—C10179.7 (6)
C2—C3—C4—C51.0 (8)C7—C8—C9—C100.7 (9)
N2—C3—C4—Cl21.7 (8)N4—C8—C9—Cl40.4 (8)
C2—C3—C4—Cl2178.2 (4)C7—C8—C9—Cl4179.4 (4)
C1—N1—C5—C40.2 (9)C6—N3—C10—C90.1 (10)
C3—C4—C5—N11.2 (9)C8—C9—C10—N30.2 (10)
Cl2—C4—C5—N1178.0 (5)Cl4—C9—C10—N3179.9 (5)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1N···Cl80.872.533.202 (6)134
N1—H1N···Cl8i0.872.543.190 (6)132
N2—H2NA···Cl7ii0.872.603.439 (5)162
N2—H2NB···Cl7iii0.872.513.338 (5)159
N3—H3N···Cl5iv0.872.783.387 (5)128
N3—H3N···Cl6v0.872.603.255 (6)133
N4—H4NA···Cl50.872.473.229 (5)146
N4—H4NB···Cl6vi0.872.463.265 (6)154
C1—H1···Cl80.942.813.356 (6)118
C5—H5···Cl8i0.942.753.308 (6)119
C10—H10···Cl5iv0.942.773.396 (6)125
Symmetry codes: (i) x+1, y+1, z+1; (ii) x+3/2, y+1/2, z+1; (iii) x+1/2, y+1/2, z; (iv) x, y+1, z; (v) x+1, y+1, z+1/2; (vi) x+1, y, z+1/2.
 

Acknowledgements

HSE is grateful to the University of Neuchâtel for their support over the years.

References

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