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The structure of the title compound, {(C5H5ClN)2[Hg3Cl8]}n, consists of 4-chloro­pyridinium cations and one-dimensional [Hg3Cl8]2− anion chains. There are two coordination environments for HgII in the inorganic chain. The first is a distorted tetra­hedral geometry made up of an HgCl2 unit with two Cl anion bridges, while the second is an octa­hedral coordination geometry consisting of an HgCl2 unit and four chloride-anion bridges. This gives rise to a novel three-layer centrosymmetric polymer. Finally, the three-dimensional network comes about through the many C—H...Cl and N—H...Cl hydrogen bonds that link the organic and inorganic layers.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270113001807/ku3085sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270113001807/ku3085Isup2.hkl
Contains datablock I

CCDC reference: 925759

Comment top

Recently, much attention has been paid to the discovery of new dielectric and ferroelectric materials, due to their wide applications as capacitors and resonators (Fu et al., 2007; Ye et al., 2009; Zhang et al., 2008). Pyridinium compounds have been used as cation substrates in the search for ferroelectric compounds. Simple pyridinium salts like PyX (py = pyridinium; X = ClO4-, ReO4-, BF4-, etc.) represent a very interesting group of hybrid organic–inorganic compounds which exhibit a range of solid–solid phase transitions due to the molecular dynamics of the pyridinium cation (Czarnecki & Małuszyńska, 2000; Hanaya et al., 2000; Wasicki et al., 1997). In the searching for potential ferroelectrics, chloromercurate(II) organic–inorganic compounds, as molecular-based materials, have received much attention due to their ferroelectric behaviour. For example, CH3NH3+.HgCl3- undergoes a ferroelectric-to-paraelectric transition due to reorientation of the CH3NH3+ cation through the order–disorder transition (Fuess et al., 1985; Jiang et al., 1995; Liesegang et al., 1995). The mercurate(II) atom has a large volume and a spherical charge distribution, as a result of the filled 4f and 5d electron shells. Also, Hg cations can have a varying number of contacts with Cl- anions, which may be much longer than the formal Hg—Cl distance but still be considered important interactions that influence the coordination of the Hg cations. So chloromercurates(II) usually exhibit a wide range of geometries, stereometries and connectivities (Grdenic, 1965; Linden et al., 1999). Among these fascinating structures, one-dimensional chloromercurate(II) inorganic chains show a great variety of architectures, and it is impossible to predict their coordination geometry due to the wide range of different Hg—Cl contacts (Aharoni et al., 1989; Bats et al., 1980; Rabe & Muller, 1999; Zabel et al., 2005). In 1999, Linden et al. (1999) reported several chloropyridinium chloromercurate(II) compounds, showing that an HgxClyn- polymer was usually made up of the subunits HgCl2, Cl-, [HgCl3]- and [HgCl4]2-. The way in which the subunits are connected results from the type of cations and the experimental conditions used. Based on these considerations, we have now used 4-chloropyridine with HgCl2 in order to extend the range of chloromercurate(II) compounds. We expected to obtain a (4-PyH)+HgCl3- structure but instead obtained the title compound, (I), a novel anionic chain architecture {[Hg3Cl8]2-} compared with other {[Hg3Cl8]2-}n structures (Terzis et al., 1985; Rabe & Muller, 1999). For example, the {[Hg3Cl8]2-}n anion reported by Terzis et al. (1985) is made up of two HgCl2 subunits and an [HgCl4]2- anion, while the basic building unit of (I) is connected by three HgCl2 and Cl- subunits which form a one-dimensional {[HgCl2]2[Cl-]2[HgCl2]}n chain (Fig. 1). Here, we report the synthesis, crystal structure and dielectric properties of (I).

Compound (I) consists of 4-chloropyridinium cations and one-dimensional inorganic anionic {[Hg3Cl8]2-}n chains. The anionic chain is made up of undistorted HgCl2, slightly distorted HgCl2 and Cl- entities, linked by different Hg—Cl contacts to form an infinite {[HgCl2]2[Cl-]2[HgCl2]}n chain (see second scheme). There are two different coordination environments about the HgII anions in the chains. Atom Hg1 lies on an inversion centre and is coordinated by four bridging chloride anions [Cl3, Cl3i, Cl3ii and Cl3iii; symmetry codes: (i) -x+1, -y+1, -z+1; (ii) -x+2, -y+1, -z+1; (iii) x-1, y, z] and two terminal chloride anions (Cl5 and Cl5i). The terminal Hg1—Cl5 and Hg1—Cl5i bond lengths are 2.305 (3) Å, forming a regular HgCl2 entity, and this distance is in accordance with other previously reported Hg—Cl terminal bonds [Reference?], while the longer bridging Hg1—Cl3(Cl3i, Cl3ii, Cl3iii) distances range from 3.130 (3) to 3.159 (3) Å and are thus obvious Hg···Cl contacts. The octahedron is slightly distorted, with Cl—Hg—Cl angles ranging from 86.30 (8) to 93.70 (8)°. Atom Hg2 is surrounded by one terminal (Cl4) and three bridging [Cl2, Cl3 and Cl2iv; symmetry code: (iv) x+1, y, z] chloride anions. Atom Hg2 has two nearly linear [Cl4—Hg2—Cl3 = 160.43 (9)°] Hg—Cl bonds and two contacts to Cl- anions, with the Hg2—Cl2(Cl2iv) distance being 2.783 (2) Å. This is much shorter than the Hg1···Cl3 contacts so it has a greater impact on the Hg2 geometry. This is a typical HgCl2+Cl- grouping distorted towards HgCl42-. The Hg2—Cl3 and Hg2—Cl4 bond lengths [2.364 (3) Å and 2.376 (3) Å] are slightly longer than Hg1—Cl5 and form a new K-shaped distorted tetrahedral structure, with the Cl—Hg2—Cl angles (except for Cl4—Hg2—Cl3) ranging from 94.23 (8) to 97.67 (8)°. Atoms Hg1 and Hg2 are linked together by Cl3 atoms, with Hg2—Cl3—Hg1 and Hg2iii—Cl3iii—Hg1 angles within the chains of 97.39 (8) and 97.22 (8)°, respectively, giving rise to a chloride corner-shared and Hg-centred three-layered chain.

There are some features of the [Hg3Cl8]n2- chains that need to be mentioned. In layers A and C, each HgCl2 molecule is linked by one Cl atom located at the mid-point perpendicular to two Hg atoms, with an Hg—Cl—Hg angle of 97.33 (7)°, which is the same as the value for Cl2—Hg1—Cl2iv. The bridging Cl atoms and the Hg atoms are all packed in a line along the a axis, forming a formal saw-tooth structure. In layer B, the linear HgCl2 units are connected together by Hg—Cl contacts to Cl3 atoms from layers A and B. Each Cl3 atom has two Hg—Cl contacts to adjacent HgII cations, with the Hg—Cl—Hg and Cl—Hg—Cl angles being 83.3 (6) and 96.7 (7)°, respectively. Compared with other bridging structures (Cecconi et al., 1998; Schunk & Thewalt, 2001; Zouari et al., 1995), the Hg—Cl—Hg angle in layer B is obviously smaller than those reported in the literature, while the Cl—Hg—Cl angle is larger. The Hg1···Hg1iii distance is 4.18 (8) Å and the Cl3i···Cl3iii distance is 4.70 (5) Å, forming an elongated parallelogram. The one-dimensional chain is centrosymmetric. The atoms generated by the symmetry point of Hg1 assemble the chain into an endless platform structure extending along the a axis (Fig. 2).

The presence of organic cations as spacers between the inorganic anions can alter the distances between the chains or layers and can also have distinctive hydrogen-bonding features which influence the structural packing (Xiao, 2010). In (I), the chains run along the a axis and are well separated by 4-chloropyridinium cations, while there is a network of intermolecular hydrogen-bonding interactions between the organic and inorganic layers. Intermolecular C3—H3···Cl4iii, N1—H1A···Cl2v, N1—H1A···Cl4vi and C4—H4···Cl5 [symmetry codes: (v) -x+1, -y+1, -z; (vi) -x+2, -y+1, -z] hydrogen bonds between the 4-chloropyridinium cations and the bridging chloride anions of the inorganic chains contribute to the formation of two-dimensional supramolecular anionic layers in the (010) plane (Fig. 3). Furthermore, N1—H1A···Cl2v and N1—H1A···Cl4vi hydrogen bonds link the 4-chloropyridinium cations in a head-to-tail manner within the chain, stabilizing the supramolecular network. Between adjacent anionic layers, the organic cations pack in an ABAB sequence as a multilayer. Layers A are composed of organic cations while layers B are composed of 4-chloropyridinium cations [This implies layers A and B are made up of the same thing. Should layers A state inorganic cations?]. In each case, [Hg3Cl8]2- has six 4-chloropyridinium cations around it, forming an impervious hexagon with [Hg3Cl8]2- located at the centre. These hydrogen bonds and other non-covalent interaction-static attracting forces, like Coulomb and van der Waals forces, link the 4-chloropyridinium cations and the anion chains into a three-dimensional network (Fig. 4).

The bond lengths and angles of 4-chloropyridinium are in agreement with those reported elsewhere in the literature (Ishihara et al., 1998; Zora et al., 1990; Zordan et al., 2005).

Our interest in the chloromercurate group is based mainly on its potential use in molecular ferro- and dielectrics. However, when we measured its dielectric properties with temperature we were unable to detect any dielectric anomalies within the temperature range 93–373 K, implying that there are no structural phase transitions within that temperature range and that the compound may not have ferroelectric properties (Ye et al., 2009; Fu et al., 2007). Further chloromercurate(II) ferroelectrics still need to be sought and explored.

Related literature top

For related literature, see: Aharoni et al. (1989); Bats et al. (1980); Cecconi et al. (1998); Czarnecki & Małuszyńska (2000); Fu et al. (2007); Fuess et al. (1985); Grdenic (1965); Hanaya et al. (2000); Ishihara et al. (1998); Jiang et al. (1995); Liesegang et al. (1995); Linden et al. (1999); Rabe & Muller (1999); Schunk & Thewalt (2001); Terzis et al. (1985); Wasicki et al. (1997); Xiao (2010); Ye et al. (2009); Zabel et al. (2005); Zhang et al. (2008); Zora et al. (1990); Zordan et al. (2005); Zouari et al. (1995).

Experimental top

4-Chloropyridinium chloride (2 mmol, 0.30 g) was dissolved in water (10 ml) and HgCl2 (2 mmol, 0.54 g) in water (10 ml) was added with stirring, and a large amount of precipitate appeared immediately. A large quantity of colourless block-shaped microcrystals of (I) were obtained by slow evaporation of a solution of the above solid in acetonitrile at room temperature in air.

Refinement top

The overall quality of the data may be poor due to the crystal quality, thus causing the value of Rint to be higher than 0.10 with a multi-scan absorption correction. H atoms were placed in calculated positions, with C—H = 0.93 Å for Csp2 atoms, and allowed to ride, with Uiso(H) = 1.2Ueq(Csp2,N).

Computing details top

Data collection: CrystalClear (Rigaku, 2005); cell refinement: CrystalClear (Rigaku, 2005); data reduction: CrystalClear (Rigaku, 2005); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. The molecular structure of (I), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. Unlabelled atoms are related to labelled atoms by the symmetry operator (-x+1, -y+1, -z+1).
[Figure 2] Fig. 2. A segment of the anionic chain in (I), showing the coordination environment of the HgII cations. [Symmetry codes: (i) -x+1, -y+1, -z+1; (ii) -x+2, -y+1, -z+1; (iii) x-1, y, z; (iv) x+1, y, z; (v) -x+1, -y+1, -z.]
[Figure 3] Fig. 3. A view of the structure of (I) in the (010) plane. The chloromercurate chains, formed by corner-shared linear [Hg3Cl8]2- trimers running along the a axis, are separated by 4-chloropyridinium cations. Dashed lines indicate hydrogen bonds. H atoms bonded to C atoms have been omitted for clarity.
[Figure 4] Fig. 4. A view of the packing of (I), along the a axis. Dashed lines indicate hydrogen bonds. H atoms bonded to C atoms have been omitted for clarity.
Poly[bis(4-chloropyridinium) tetra-µ2-chlorido-tetrachloridotrimercury(II)] top
Crystal data top
(C5H5ClN)2[Hg3Cl8]Z = 1
Mr = 1114.47F(000) = 494
Triclinic, P1Dx = 3.076 Mg m3
Hall symbol: -P 1Mo Kα radiation, λ = 0.71073 Å
a = 4.1792 (8) ÅCell parameters from 5679 reflections
b = 11.618 (2) Åθ = 3.2–26.0°
c = 13.238 (3) ŵ = 20.20 mm1
α = 70.44 (3)°T = 298 K
β = 83.71 (3)°Block, colourless
γ = 89.91 (3)°0.30 × 0.28 × 0.26 mm
V = 601.6 (2) Å3
Data collection top
Rigaku Mercury2
diffractometer
2364 independent reflections
Radiation source: fine-focus sealed tube1950 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.101
Detector resolution: 13.6612 pixels mm-1θmax = 26.0°, θmin = 3.2°
CCD profile fitting scansh = 55
Absorption correction: multi-scan
(CrystalClear; Rigaku, 2005)
k = 1414
Tmin = 0.065, Tmax = 0.077l = 1616
5558 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)] = 0.050H-atom parameters constrained
wR(F2) = 0.104 w = 1/[σ2(Fo2) + (0.P)2]
where P = (Fo2 + 2Fc2)/3
S = 0.92(Δ/σ)max = 0.001
2357 reflectionsΔρmax = 2.88 e Å3
116 parametersΔρmin = 1.54 e Å3
0 restraintsExtinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.0167 (7)
Crystal data top
(C5H5ClN)2[Hg3Cl8]γ = 89.91 (3)°
Mr = 1114.47V = 601.6 (2) Å3
Triclinic, P1Z = 1
a = 4.1792 (8) ÅMo Kα radiation
b = 11.618 (2) ŵ = 20.20 mm1
c = 13.238 (3) ÅT = 298 K
α = 70.44 (3)°0.30 × 0.28 × 0.26 mm
β = 83.71 (3)°
Data collection top
Rigaku Mercury2
diffractometer
2364 independent reflections
Absorption correction: multi-scan
(CrystalClear; Rigaku, 2005)
1950 reflections with I > 2σ(I)
Tmin = 0.065, Tmax = 0.077Rint = 0.101
5558 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0500 restraints
wR(F2) = 0.104H-atom parameters constrained
S = 0.92Δρmax = 2.88 e Å3
2357 reflectionsΔρmin = 1.54 e Å3
116 parameters
Special details top

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 (Å2) top
xyzUiso*/Ueq
C10.038 (2)0.0613 (10)0.2495 (9)0.062 (3)
H10.13630.01520.28680.074*
C20.119 (3)0.0861 (10)0.1463 (9)0.062 (3)
H20.12230.02690.11330.075*
C30.256 (2)0.2860 (11)0.1420 (9)0.051 (3)
H30.35880.36160.10450.061*
C40.1020 (19)0.2671 (9)0.2405 (8)0.045 (3)
H40.09190.32870.27090.055*
C50.042 (2)0.1509 (10)0.2959 (8)0.046 (3)
Cl10.2423 (8)0.1263 (4)0.4224 (3)0.0859 (13)
Cl20.6221 (5)0.8496 (2)0.13064 (19)0.0374 (6)
Cl31.0311 (6)0.7076 (3)0.3926 (2)0.0431 (6)
Cl41.1536 (6)0.5988 (2)0.0817 (2)0.0427 (6)
Cl50.5572 (6)0.4635 (2)0.3383 (2)0.0436 (7)
Hg10.50000.50000.50000.0415 (2)
Hg21.09239 (8)0.68857 (3)0.21839 (3)0.0392 (2)
N10.2625 (19)0.1964 (9)0.0952 (7)0.061 (3)
H1A0.36150.21170.03130.073*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
C10.082 (8)0.041 (7)0.064 (8)0.007 (6)0.000 (6)0.021 (6)
C20.088 (8)0.058 (8)0.067 (8)0.000 (7)0.015 (6)0.054 (6)
C30.063 (6)0.036 (7)0.054 (7)0.003 (5)0.002 (5)0.020 (5)
C40.050 (5)0.041 (6)0.053 (6)0.007 (5)0.005 (5)0.027 (5)
C50.056 (6)0.046 (7)0.039 (6)0.004 (5)0.007 (4)0.017 (5)
Cl10.110 (3)0.083 (3)0.0488 (19)0.004 (2)0.0178 (17)0.0098 (17)
Cl20.0419 (11)0.0305 (13)0.0465 (14)0.0020 (10)0.0066 (10)0.0212 (10)
Cl30.0557 (14)0.0477 (16)0.0351 (14)0.0003 (12)0.0089 (11)0.0249 (12)
Cl40.0615 (14)0.0384 (15)0.0386 (13)0.0029 (12)0.0062 (11)0.0264 (11)
Cl50.0554 (14)0.0488 (16)0.0346 (14)0.0019 (13)0.0056 (11)0.0245 (11)
Hg10.0467 (3)0.0528 (4)0.0330 (3)0.0012 (3)0.0053 (2)0.0246 (3)
Hg20.0482 (3)0.0414 (3)0.0348 (3)0.0009 (2)0.00551 (18)0.0218 (2)
N10.062 (5)0.085 (8)0.032 (5)0.009 (6)0.017 (4)0.011 (5)
Geometric parameters (Å, º) top
C1—C51.373 (16)C5—Cl11.722 (10)
C1—C21.386 (14)Cl2—Hg2i2.783 (2)
C1—H10.9300Cl2—Hg22.783 (2)
C2—N11.339 (12)Cl3—Hg22.376 (3)
C2—H20.9300Cl4—Hg22.365 (3)
C3—C41.337 (13)Cl5—Hg12.305 (3)
C3—N11.377 (14)Hg1—Cl5ii2.305 (3)
C3—H30.9299Hg2—Cl2iii2.783 (2)
C4—C51.401 (12)N1—H1A0.8600
C4—H40.9300
C5—C1—C2118.8 (10)C1—C5—Cl1120.7 (8)
C5—C1—H1120.9C4—C5—Cl1117.5 (9)
C2—C1—H1120.3Hg2i—Cl2—Hg297.31 (7)
N1—C2—C1119.0 (11)Cl5ii—Hg1—Cl5180.00 (3)
N1—C2—H2120.9Cl4—Hg2—Cl3160.44 (10)
C1—C2—H2120.1Cl4—Hg2—Cl2iii94.23 (8)
C4—C3—N1121.3 (10)Cl3—Hg2—Cl2iii97.66 (9)
C4—C3—H3118.9Cl4—Hg2—Cl296.28 (9)
N1—C3—H3119.8Cl3—Hg2—Cl297.54 (9)
C3—C4—C5117.3 (11)Cl2iii—Hg2—Cl297.31 (7)
C3—C4—H4121.1C2—N1—C3121.8 (9)
C5—C4—H4121.6C2—N1—H1A119.1
C1—C5—C4121.7 (10)C3—N1—H1A119.1
C5—C1—C2—N10.3 (16)Hg2i—Cl2—Hg2—Cl484.90 (9)
N1—C3—C4—C52.6 (15)Hg2i—Cl2—Hg2—Cl381.22 (10)
C2—C1—C5—C41.5 (17)Hg2i—Cl2—Hg2—Cl2iii180.0
C2—C1—C5—Cl1178.2 (8)C1—C2—N1—C30.6 (15)
C3—C4—C5—C12.9 (15)C4—C3—N1—C20.9 (16)
C3—C4—C5—Cl1179.7 (8)
Symmetry codes: (i) x1, y, z; (ii) x+1, y+1, z+1; (iii) x+1, y, z.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1A···Cl2iv0.862.473.195 (10)142
N1—H1A···Cl4v0.862.893.483 (9)128
C3—H3···Cl4i0.932.823.486 (12)129
C4—H4···Cl50.932.893.611 (10)135
Symmetry codes: (i) x1, y, z; (iv) x+1, y+1, z; (v) x+2, y+1, z.

Experimental details

Crystal data
Chemical formula(C5H5ClN)2[Hg3Cl8]
Mr1114.47
Crystal system, space groupTriclinic, P1
Temperature (K)298
a, b, c (Å)4.1792 (8), 11.618 (2), 13.238 (3)
α, β, γ (°)70.44 (3), 83.71 (3), 89.91 (3)
V3)601.6 (2)
Z1
Radiation typeMo Kα
µ (mm1)20.20
Crystal size (mm)0.30 × 0.28 × 0.26
Data collection
DiffractometerRigaku Mercury2
diffractometer
Absorption correctionMulti-scan
(CrystalClear; Rigaku, 2005)
Tmin, Tmax0.065, 0.077
No. of measured, independent and
observed [I > 2σ(I)] reflections
5558, 2364, 1950
Rint0.101
(sin θ/λ)max1)0.617
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.050, 0.104, 0.92
No. of reflections2357
No. of parameters116
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)2.88, 1.54

Computer programs: CrystalClear (Rigaku, 2005), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), SHELXTL (Sheldrick, 2008).

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1A···Cl2i0.862.473.195 (10)142.4
N1—H1A···Cl4ii0.862.893.483 (9)128.0
C3—H3···Cl4iii0.932.823.486 (12)129.4
C4—H4···Cl50.932.893.611 (10)134.8
Symmetry codes: (i) x+1, y+1, z; (ii) x+2, y+1, z; (iii) x1, y, z.
 

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