Bis(pyridinium) tetra­chlorido­zincate(II), [Hpy]2[ZnCl4]

Reuter, H.

doi:10.1107/S241431462601000X

metal-organic compounds

IUCrDATA

ISSN: 2414-3146

Volume 11| Part 9| September 2026| x261000

https://doi.org/10.1107/S241431462601000X

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Bis(pyridinium) tetrachloridozincate(II), [Hpy]₂[ZnCl₄]

Hans Reuter ^a ^*

^aChemistry, Osnabrück University, Barbarastr. 7, 49069 Osnabrück, Germany
^*Correspondence e-mail: [email protected]

Edited by R. J. Butcher, Howard University, USA (Received 19 September 2026; accepted 25 September 2026; online 30 September 2026)

Single crystals of the title compound, (C₅H₆N)₂[ZnCl₄] or [Hpy]₂[ZnCl₄], were grown from an aqueous solution of pyridinium chloride and zinc dichloride. The compound is isostructural with the corresponding cobalt compound and exhibits an almost tetrahedral [ZnCl₄]²⁻ anion and two different pyridinium cations. The structure is described with respect to the bond lengths and angles of the anion and the π–π interactions between the cations, whilst mention is made of the N—H⋯Cl and C—H⋯Cl interactions already known from the cobalt compound.

Keywords: crystal structure; hydrogen bonds; tetrachloridozincate; π–π interactions.

CCDC reference: 2590726

Structure description

The title compound is isostructural with the analogous cobalt compound (Felloni et al., 2004 ) and crystallizes in the triclinic space group P $[\overline{1}]$ with one formula unit in the asymmetric unit (Fig. 1). The zinc atom is almost tetrahedrally [〈(Cl—Zn—Cl) = 105.62 (1)–111.91 (1)°, 〈(Cl—Zn—Cl)_mean = 109.5 (23)°] coordinated from four chlorine atoms. The zinc–chlorine distances are, on average, slightly shorter [d(Zn—Cl)_mean = 2.273 (11) Å] than the cobalt-chlorine distances [d(Co—Cl)_mean = 2.276 (7) Å], but vary much more widely [2.2605 (3) − 2.2862 (3) Å] than the latter. Zn—Cl distances of similar length and variation can be found, for example, in the compound with the 4,4′-bipyridinium ion [d(Zn—Cl)_mean = 2.275 (27) Å] (Gillon et al., 2000 ) and in the compound with the 3-chloropyridinium ion [d(Zn—Cl)_mean = 2.272 (14) Å] (Mínguez Espallargas et al., 2009 ).

Figure 1
Asymmetric unit of the crystal structure of [Hpy]₂[ZnCl₄] with atom numbering according to the isostructural cobalt compound. With the exception of the hydrogen atoms, which are shown as spheres of arbitrary radius, all other atoms are drawn as anisotropic displacement ellipsoids at the 50% probability level.

As the publication on the cobalt compound (Felloni et al., 2004) describes the key aspects of the crystal structure, particularly with regard to the pattern of N—H⋯Cl hydrogen bonds and C—H⋯Cl contacts, there is no need to provide a detailed description of this here. All the necessary information to these supramolecular interactions can be found in Table 1 and can be compared directly with the values reported for the cobalt compound, as the asymmetric unit has been adjusted in terms of atomic numbering and its position within the unit cell.

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N11—H11⋯Cl2	0.88	2.51	3.211 (1)	137
N11—H11⋯Cl2ⁱ	0.88	2.73	3.350 (1)	129
C12—H12⋯Cl2	0.95	2.97	3.443 (1)	112
C13—H13⋯Cl2ⁱⁱ	0.95	2.94	3.584 (1)	127
C15—H15⋯Cl1ⁱⁱⁱ	0.95	2.96	3.576 (1)	124
C16—H16⋯Cl2ⁱ	0.95	2.84	3.417 (1)	120
N21—H21⋯Cl1	0.88	2.69	3.337 (1)	132
N21—H21⋯Cl4	0.88	2.53	3.246 (1)	139
C22—H22⋯Cl1	0.95	2.83	3.416 (1)	121
C22—H22⋯Cl4^iv	0.95	2.97	3.592 (1)	125
C23—H23⋯Cl4^iv	0.95	2.90	3.559 (1)	128
C25—H25⋯Cl3^v	0.95	2.80	3.552 (1)	137
C26—H26⋯Cl4	0.95	2.96	3.466 (2)	115
Symmetry codes: (i) ; (ii) ; (iii) ; (iv) ; (v) .

However, another aspect is presented here that is not given sufficient attention in the publication on the cobalt compound. Within the crystal structure (Fig. 2), the two pyridinium ions are arranged such that they partially overlap: Hpy(1) on one side, Hpy(2) on both sides. In all three cases, the relevant element of symmetry is a center of symmetry. In the case of Hpy(1), this is located at Wyckhoff position e; in the case of Hpy(2), at Wyckhoff positions c and h. The centers of symmetry ensure that the planes of the two neighboring pyridinium ions are exactly parallel to one another, with the nitrogen atoms facing in opposite directions.

Figure 2
Ball-and-stick model of the ions in the crystal structure of the title compound showing their three-dimensional packing when looking down the a axis. The layers of the two different pyridinium ions are labeled and the relevant centers of symmetry (black dots) marked with Wyckhoff letters. Color code: Zn = light blue, Cl = yellow–green, N = dark blue, C = dark gray, H = white.

It can be seen from Fig. 3 that the more the pyridinium ions overlap, the greater the distance between the planes becomes. The different distances between the nitrogen atoms in these arrangements is also evident.

Figure 3
Different representations of the cation stacking. (left) Space-filling model with stick model overlayed; side-view with distances between the least-squares planes (Å, black values). (right) Ball-and-stick models of the centrosymmetric dimers looking down on the least-square planes with distances (Å, blue values])between the nitrogen atoms and positions of the relevant centers of symmetry (black dots) marked with the Wyckhoff letters.

Synthesis and crystallization

The title compound was synthesized by dissolving equimolar quantities of zinc chloride and pyridinium chloride in water. When the solvent evaporates, the compound crystallizes in transparent, slightly green needles.

Refinement

Crystal data,data collection and structure refinement details are summarized in Table 2. Once it had become apparent that the compound was isostructural with the cobalt compound, its asymmetric unit was used to describe the structure.

Table 2
Experimental details

Crystal data
Chemical formula	(C₅H₆N)₂[ZnCl₄]
M_r	367.39
Crystal system, space group	Triclinic, P $[\overline{1}]$
Temperature (K)	100
a, b, c (Å)	7.5711 (3), 7.9451 (3), 12.3798 (5)
α, β, γ (°)	88.942 (2), 83.518 (2), 79.959 (2)
V (Å³)	728.59 (5)
Z	2
Radiation type	Mo Kα
μ (mm⁻¹)	2.40
Crystal size (mm)	0.39 × 0.24 × 0.19

Data collection
Diffractometer	Bruker APEXII CCD
Absorption correction	Multi-scan (SADABS; Krause et al., 2015 )
T_min, T_max	0.498, 0.523
No. of measured, independent and observed [I > 2σ(I)] reflections	82340, 4103, 3846
R_int	0.030
(sin θ/λ)_max (Å⁻¹)	0.696

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.016, 0.041, 1.07
No. of reflections	4103
No. of parameters	156
H-atom treatment	Only H-atom displacement parameters refined
Δρ_max, Δρ_min (e Å⁻³)	0.38, −0.28
Computer programs: APEX2 and SAINT (Bruker, 2009 ), SHELXS97 (Sheldrick, 2008 ), SHELXL2014/7 (Sheldrick, 2015 ), DIAMOND (Brandenburg, 2006 ), Mercury (Macrae et al., 2020 ) and publCIF (Westrip, 2010 ).

Structural data

CCDC reference: 2590726

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S241431462601000X/bv4063sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S241431462601000X/bv4063Isup2.hkl

checkCIF report

Computing details top

Bis(pyridinium) tetrachloridozincate(II) top

Crystal data top

(C₅H₆N)₂[ZnCl₄]	Z = 2
M_r = 367.39	F(000) = 368
Triclinic, P1	D_x = 1.675 Mg m⁻³
a = 7.5711 (3) Å	Mo Kα radiation, λ = 0.71073 Å
b = 7.9451 (3) Å	Cell parameters from 9982 reflections
c = 12.3798 (5) Å	θ = 2.6–29.6°
α = 88.942 (2)°	µ = 2.40 mm⁻¹
β = 83.518 (2)°	T = 100 K
γ = 79.959 (2)°	Needle, green
V = 728.59 (5) Å³	0.39 × 0.24 × 0.19 mm

Data collection top

Bruker APEXII CCD diffractometer	3846 reflections with I > 2σ(I)
φ and ω scans	R_int = 0.030
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	θ_max = 29.6°, θ_min = 2.6°
T_min = 0.498, T_max = 0.523	h = −10→10
82340 measured reflections	k = −11→11
4103 independent reflections	l = −17→17

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.016	Only H-atom displacement parameters refined
wR(F²) = 0.041	w = 1/[σ²(F_o²) + (0.0205P)² + 0.2351P] where P = (F_o² + 2F_c²)/3
S = 1.07	(Δ/σ)_max = 0.002
4103 reflections	Δρ_max = 0.38 e Å⁻³
156 parameters	Δρ_min = −0.28 e Å⁻³
0 restraints

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. The H atoms were refined in idealized geometries and allowed to ride on the parent carbon [d(C—H) = 0.95 Å] and nitrogen atoms [d(N—H) = 0.88 Å] with one common isotropic temperature factor for each of the two pyridinium ions.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
Zn1	0.94436 (2)	0.17307 (2)	0.22056 (2)	0.01280 (4)
Cl1	0.67207 (3)	0.09965 (3)	0.19775 (2)	0.01488 (5)
Cl2	1.10183 (3)	0.18295 (3)	0.05356 (2)	0.01455 (5)
Cl3	0.90410 (3)	0.43146 (3)	0.30190 (2)	0.01870 (6)
Cl4	1.08368 (3)	−0.03785 (3)	0.32370 (2)	0.01898 (6)
N11	0.75046 (12)	0.23776 (12)	−0.07461 (8)	0.01706 (18)
H11	0.8367	0.1659	−0.0479	0.0247 (15)*
C12	0.77721 (15)	0.39734 (15)	−0.09665 (9)	0.0185 (2)
H12	0.8877	0.4310	−0.0845	0.0247 (15)*
C13	0.64300 (15)	0.51229 (14)	−0.13719 (9)	0.0185 (2)
H13	0.6597	0.6262	−0.1534	0.0247 (15)*
C14	0.48320 (15)	0.45976 (14)	−0.15402 (9)	0.0170 (2)
H14	0.3889	0.5381	−0.1812	0.0247 (15)*
C15	0.46079 (14)	0.29270 (14)	−0.13117 (9)	0.0170 (2)
H15	0.3518	0.2555	−0.1429	0.0247 (15)*
C16	0.59836 (15)	0.18200 (14)	−0.09133 (9)	0.0181 (2)
H16	0.5860	0.0668	−0.0757	0.0247 (15)*
N21	0.70751 (13)	−0.16465 (12)	0.40981 (8)	0.01933 (19)
H21	0.7710	−0.1133	0.3597	0.0294 (17)*
C22	0.53087 (16)	−0.15652 (14)	0.40250 (9)	0.0194 (2)
H22	0.4764	−0.0965	0.3443	0.0294 (17)*
C23	0.42975 (15)	−0.23567 (14)	0.47987 (9)	0.0188 (2)
H23	0.3045	−0.2314	0.4757	0.0294 (17)*
C24	0.51212 (15)	−0.32184 (14)	0.56405 (9)	0.0181 (2)
H24	0.4433	−0.3767	0.6183	0.0294 (17)*
C25	0.69495 (16)	−0.32800 (15)	0.56911 (9)	0.0210 (2)
H25	0.7528	−0.3871	0.6265	0.0294 (17)*
C26	0.79136 (15)	−0.24706 (15)	0.48961 (10)	0.0211 (2)
H26	0.9169	−0.2498	0.4915	0.0294 (17)*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Zn1	0.01176 (6)	0.01293 (6)	0.01405 (6)	−0.00272 (4)	−0.00215 (4)	0.00042 (4)
Cl1	0.01383 (11)	0.01502 (11)	0.01738 (11)	−0.00575 (8)	−0.00378 (9)	0.00149 (8)
Cl2	0.01337 (11)	0.01618 (11)	0.01457 (11)	−0.00401 (8)	−0.00148 (8)	0.00135 (8)
Cl3	0.01431 (11)	0.01759 (12)	0.02475 (13)	−0.00271 (9)	−0.00354 (9)	−0.00729 (10)
Cl4	0.01502 (11)	0.02239 (13)	0.01953 (12)	−0.00225 (9)	−0.00462 (9)	0.00743 (10)
N11	0.0159 (4)	0.0177 (4)	0.0164 (4)	0.0011 (3)	−0.0035 (3)	0.0023 (3)
C12	0.0170 (5)	0.0223 (5)	0.0180 (5)	−0.0073 (4)	−0.0037 (4)	0.0005 (4)
C13	0.0224 (5)	0.0154 (5)	0.0194 (5)	−0.0064 (4)	−0.0049 (4)	0.0030 (4)
C14	0.0173 (5)	0.0170 (5)	0.0165 (5)	−0.0013 (4)	−0.0042 (4)	0.0013 (4)
C15	0.0154 (5)	0.0191 (5)	0.0174 (5)	−0.0059 (4)	−0.0014 (4)	−0.0018 (4)
C16	0.0205 (5)	0.0141 (5)	0.0195 (5)	−0.0047 (4)	0.0006 (4)	0.0010 (4)
N21	0.0232 (5)	0.0171 (4)	0.0178 (4)	−0.0080 (4)	0.0051 (4)	−0.0022 (3)
C22	0.0252 (6)	0.0161 (5)	0.0174 (5)	−0.0035 (4)	−0.0043 (4)	0.0000 (4)
C23	0.0155 (5)	0.0189 (5)	0.0226 (5)	−0.0039 (4)	−0.0036 (4)	−0.0007 (4)
C24	0.0195 (5)	0.0186 (5)	0.0163 (5)	−0.0052 (4)	0.0007 (4)	−0.0002 (4)
C25	0.0207 (5)	0.0246 (6)	0.0180 (5)	−0.0024 (4)	−0.0054 (4)	0.0000 (4)
C26	0.0146 (5)	0.0231 (6)	0.0259 (6)	−0.0047 (4)	−0.0007 (4)	−0.0061 (4)

Geometric parameters (Å, º) top

Zn1—Cl3	2.2605 (3)	C15—H15	0.9500
Zn1—Cl4	2.2715 (3)	C16—H16	0.9500
Zn1—Cl2	2.2742 (3)	N21—C26	1.3344 (16)
Zn1—Cl1	2.2862 (3)	N21—C22	1.3408 (15)
N11—C12	1.3369 (15)	N21—H21	0.8800
N11—C16	1.3418 (14)	C22—C23	1.3708 (16)
N11—H11	0.8800	C22—H22	0.9500
C12—C13	1.3759 (16)	C23—C24	1.3840 (16)
C12—H12	0.9500	C23—H23	0.9500
C13—C14	1.3847 (15)	C24—C25	1.3850 (16)
C13—H13	0.9500	C24—H24	0.9500
C14—C15	1.3873 (15)	C25—C26	1.3759 (17)
C14—H14	0.9500	C25—H25	0.9500
C15—C16	1.3719 (15)	C26—H26	0.9500

Cl3—Zn1—Cl4	111.911 (12)	N11—C16—C15	119.44 (10)
Cl3—Zn1—Cl2	109.683 (11)	N11—C16—H16	120.3
Cl4—Zn1—Cl2	111.059 (11)	C15—C16—H16	120.3
Cl3—Zn1—Cl1	110.461 (10)	C26—N21—C22	122.99 (10)
Cl4—Zn1—Cl1	105.621 (11)	C26—N21—H21	118.5
Cl2—Zn1—Cl1	107.971 (10)	C22—N21—H21	118.5
C12—N11—C16	123.13 (10)	N21—C22—C23	119.32 (10)
C12—N11—H11	118.4	N21—C22—H22	120.3
C16—N11—H11	118.4	C23—C22—H22	120.3
N11—C12—C13	119.30 (10)	C22—C23—C24	119.27 (10)
N11—C12—H12	120.4	C22—C23—H23	120.4
C13—C12—H12	120.4	C24—C23—H23	120.4
C12—C13—C14	119.11 (10)	C23—C24—C25	119.95 (10)
C12—C13—H13	120.4	C23—C24—H24	120.0
C14—C13—H13	120.4	C25—C24—H24	120.0
C13—C14—C15	120.01 (10)	C26—C25—C24	118.84 (11)
C13—C14—H14	120.0	C26—C25—H25	120.6
C15—C14—H14	120.0	C24—C25—H25	120.6
C16—C15—C14	118.99 (10)	N21—C26—C25	119.63 (10)
C16—C15—H15	120.5	N21—C26—H26	120.2
C14—C15—H15	120.5	C25—C26—H26	120.2

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N11—H11···Cl2	0.88	2.51	3.211 (1)	137
N11—H11···Cl2ⁱ	0.88	2.73	3.350 (1)	129
C12—H12···Cl2	0.95	2.97	3.443 (1)	112
C13—H13···Cl2ⁱⁱ	0.95	2.94	3.584 (1)	127
C15—H15···Cl1ⁱⁱⁱ	0.95	2.96	3.576 (1)	124
C16—H16···Cl2ⁱ	0.95	2.84	3.417 (1)	120
N21—H21···Cl1	0.88	2.69	3.337 (1)	132
N21—H21···Cl4	0.88	2.53	3.246 (1)	139
C22—H22···Cl1	0.95	2.83	3.416 (1)	121
C22—H22···Cl4^iv	0.95	2.97	3.592 (1)	125
C23—H23···Cl4^iv	0.95	2.90	3.559 (1)	128
C25—H25···Cl3^v	0.95	2.80	3.552 (1)	137
C26—H26···Cl4	0.95	2.96	3.466 (2)	115

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

Acknowledgements

The Deutsche Forschungsgemeinschaft and the Government of Lower-Saxony are thanked for the funding of the diffractometer.

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