research communications\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

ISSN: 2056-9890

New refinement of the crystal structure of Zn(NH3)2Cl2 at 100 K

aLaboratory of Physics of Complex Matter, Ecole Polytechnique Fédérale de Lausanne, Switzerland, and bCrystal Growth Facility, Ecole Polytechnique Fédérale de Lausanne, Switzerland
*Correspondence e-mail:

Edited by M. Weil, Vienna University of Technology, Austria (Received 15 August 2019; accepted 26 August 2019; online 30 August 2019)

The crystal structure of [ZnCl2(NH3)2], diamminedi­chlorido­zinc, was re-investigated at low temperature, revealing the positions of the hydrogen atoms and thus a deeper insight into the hydrogen-bonding scheme in the crystal packing. In comparison with previous crystal structure determinations [MacGillavry & Bijvoet (1936[MacGillavry, C. H. & Bijvoet, J. M. (1936). Z. Kristallogr. 94, 249-255.]). Z. Kristallogr. 94, 249–255; Yamaguchi & Lindqvist (1981[Yamaguchi, T. & Lindqvist, O. (1981). Acta Chem. Scand. 35, 727-728.]). Acta Chem. Scand. 35, 727–728], an improved precision of the structural parameters was achieved. In the crystal, tetra­hedral [Zn(NH3)2Cl2] units (point-group symmetry mm2) are linked through N—H⋯Cl hydrogen bonds into a three-dimensional network.

1. Chemical context

Zn(NH3)2Cl2 is found in discharged zinc–air batteries. It is formed by dissolution of the zinc electrode in an ZnCl2–NH4Cl electrolyte. At high Zn2+ concentrations, the cations subsequently undergo complex formation with NH3 and Cl (Clark et al., 2017[Clark, S., Latz, A. & Horstmann, B. (2017). ChemSusChem, 10, 4735-4747.]). Moreover, in the last century, Zn(NH3)nCl2 phases with n = 0.167–6 have been intensively investigated since these materials appear to be by-products of hydro­cracking of heavy-oil fractions. The monoammine salt with n = 1 and the diammine salt with n = 2 are the most studied members in this family. Thermal stability, thermomechanical and thermogravimetric behaviour are well documented for these systems (Gardner et al., 1989[Gardner, P. J., Pang, P. & Preston, S. (1989). Thermochim. Acta, 138, 371-374.]).

The crystal-structure model of Zn(NH3)2Cl2 was to this day incomplete, lacking the positions of hydrogen atoms. The crystal structure of Zn(NH3)2Cl2 was originally determined by MacGillavry & Bijvoet (1936[MacGillavry, C. H. & Bijvoet, J. M. (1936). Z. Kristallogr. 94, 249-255.]) without refinement of atomic positions [COD number ID 1010197; ICSD number 26136; PDF4 number 01-074-0506]. This incompleteness was rather normal considering the X-ray techniques and measurement conditions at that time. An improved structure model was obtained decades later from a room-temperature data set collected on a four-circle diffractometer by Yamaguchi & Lindqvist (1981[Yamaguchi, T. & Lindqvist, O. (1981). Acta Chem. Scand. 35, 727-728.]), however without hydrogen-atom positions [PDF4 number 04-015-4717]. One more record of this phase in PDF4 [number 00-024-1435] can be found, however with a very limited X-ray powder diffraction pattern range from 5–63°/2θ, which is unsuitable for Rietveld refinement.

Large single crystals of Zn(NH3)2Cl2 were obtained as a side product of a chemical vapour transport (CVT) reaction, which allowed the reinvestigation of the crystal structure at low temperature with a particular focus on determination of the H-atom positions.

2. Structural commentary

As shown in Fig. 1[link], the new structure refinement of Zn(NH3)2Cl2 (100 K data) confirms the former model by Yamaguchi & Lindqvist (1981[Yamaguchi, T. & Lindqvist, O. (1981). Acta Chem. Scand. 35, 727-728.]). The small shrinkage of the unit cell at low temperature is mainly due to lattice dynamics. However, the bond lengths within the Zn(NH3)2Cl2 tetra­hedron refined from 100 K data are similar to the ones obtained from room-temperature data, but with higher precision. This confirms that the tetra­hedron is a very rigid building block of the structure (Fig. 2[link]). Two independent H atoms, one in a general position (H1A) and one on a mirror plane (H1B), bond to the nitro­gen atom with refined bond lengths of N1—H1A = 0.825 (17) Å and N1—H1B = 0.74 (4) Å, respectively. Hydrogen-bonding inter­actions of weak-to-medium strengths (Table 1[link]) between the NH3 group and the Cl ligands of adjacent tetra­hedra lead to formation of a three-dimensional network, as shown in Fig. 3[link].

Table 1
Hydrogen-bond geometry (Å, °)

N1—H1A⋯Cl1i 0.825 (17) 2.806 (18) 3.4552 (9) 137.0 (17)
N1—H1A⋯Cl1ii 0.825 (17) 2.897 (18) 3.5505 (9) 137.6 (16)
N1—H1B⋯Cl1iii 0.74 (4) 2.95 (3) 3.5556 (10) 141 (1)
N1—H1B⋯Cl1iv 0.74 (4) 2.95 (3) 3.5556 (10) 141 (1)
Symmetry codes: (i) -x+1, -y+1, -z+1; (ii) [-x+{\script{1\over 2}}, -y+1, z-{\script{1\over 2}}]; (iii) [-x+{\script{1\over 2}}, -y+{\script{1\over 2}}, -z+{\script{3\over 2}}]; (iv) [x-{\script{1\over 2}}, y, -z+{\script{3\over 2}}].
[Figure 1]
Figure 1
The tetra­hedral [Zn(NH3)2Cl2] group. H atoms (cyan circles) are plotted with arbitrary size. [Symmetry code: (A) 1 − x, [{1\over 2}] − y, z.].
[Figure 2]
Figure 2
Comparison of the [ZnN2Cl2] tetra­hedra from the room temperature data (left; Yamaguchi & Lindqvist, 1981[Yamaguchi, T. & Lindqvist, O. (1981). Acta Chem. Scand. 35, 727-728.]) and the present 100 K data (right). Bond lengths for the room-temperature data were calculated with DIAMOND (Brandenburg, 2006[Brandenburg, K. (2006). DIAMOND. Crystal Impact GbR, Bonn, Germany.]).
[Figure 3]
Figure 3
Packing view along the b axis (left) and the c axis (right), showing N—H⋯Cl inter­actions between adjacent [Zn(NH3)2Cl2] tetra­hedra.

3. Synthesis and crystallization

Zn(NH3)2Cl2 was obtained during the course of a chemical vapour transport experiment. Prior to use, a silica tube sealed at one end (Ø = 15 mm, wall thickness = 2 mm) was heated under vacuum to 1073 K overnight. Zinc oxide (317 mg) and previously dried ammonium chloride (190 mg) were pressed into pellets and put into the pretreated silica tube. After evacuation to 10−6 mbar, the tube was sealed and placed into a horizontal tube furnace. The temperature at the source was slowly heated to 1173 K and maintained at this value for the whole duration of growth. At the low-temperature zone (873 K), a colourless powder mixed with high-quality single crystals of Zn(NH3)2Cl2 with an irregular morphology was collected after complete cooling to room temperature. Since the thermal stability of Zn(NH3)2Cl2 is limited as it already decomposes at 463 K (Gardner et al., 1989[Gardner, P. J., Pang, P. & Preston, S. (1989). Thermochim. Acta, 138, 371-374.]), it is very likely that Zn(NH3)2Cl2 crystallized at the very end of the cooling process.

4. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2[link]. Unlike the two previous refinements in space group Imam, the unit cell was chosen to be in the standard setting (Imma) for space group No. 74. Three reflections (020, 002, 004) affected by the incident beam-stop were omitted. The two H atoms were refined freely.

Table 2
Experimental details

Crystal data
Chemical formula [ZnCl2(NH3)2]
Mr 170.34
Crystal system, space group Orthorhombic, Imma
Temperature (K) 100
a, b, c (Å) 7.7077 (2), 8.0226 (2), 8.4526 (3)
V3) 522.67 (3)
Z 4
Radiation type Mo Kα
μ (mm−1) 5.56
Crystal size (mm) 0.26 × 0.18 × 0.16
Data collection
Diffractometer Rigaku SuperNOVA
Absorption correction Analytical (CrysAlis PRO; Rigaku OD, 2019[Rigaku OD (2019). CrysAlis PRO. Rigaku Oxford Diffraction, Yarnton, England.])
Tmin, Tmax 0.277, 0.454
No. of measured, independent and observed [I > 2σ(I)] reflections 2303, 708, 678
Rint 0.017
(sin θ/λ)max−1) 0.833
R[F2 > 2σ(F2)], wR(F2), S 0.015, 0.036, 1.04
No. of reflections 708
No. of parameters 25
H-atom treatment All H-atom parameters refined
Δρmax, Δρmin (e Å−3) 0.50, −0.55
Computer programs: CrysAlis PRO (Rigaku OD, 2019[Rigaku OD (2019). CrysAlis PRO. Rigaku Oxford Diffraction, Yarnton, England.]), SHELXT (Sheldrick, 2015a[Sheldrick, G. M. (2015a). Acta Cryst. A71, 3-8.]), SHELXL2018 (Sheldrick, 2015b[Sheldrick, G. M. (2015b). Acta Cryst. C71, 3-8.]), DIAMOND (Brandenburg, 2006[Brandenburg, K. (2006). DIAMOND. Crystal Impact GbR, Bonn, Germany.]) and publCIF (Westrip, 2010[Westrip, S. P. (2010). J. Appl. Cryst. 43, 920-925.]).

Supporting information

Computing details top

Data collection: CrysAlis PRO (Rigaku OD, 2019); cell refinement: CrysAlis PRO (Rigaku OD, 2019); data reduction: CrysAlis PRO (Rigaku OD, 2019); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2018 (Sheldrick, 2015b); molecular graphics: DIAMOND (Brandenburg, 2006); software used to prepare material for publication: publCIF (Westrip, 2010).

Diamminedichloridozinc top
Crystal data top
[ZnCl2(NH3)2]Dx = 2.165 Mg m3
Mr = 170.34Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, ImmaCell parameters from 1597 reflections
a = 7.7077 (2) Åθ = 3.6–37.4°
b = 8.0226 (2) ŵ = 5.56 mm1
c = 8.4526 (3) ÅT = 100 K
V = 522.67 (3) Å3Irregular, colourless
Z = 40.26 × 0.18 × 0.16 mm
F(000) = 336
Data collection top
Rigaku SuperNOVA
678 reflections with I > 2σ(I)
Radiation source: micro-focus sealed X-ray tubeRint = 0.017
ω scansθmax = 36.3°, θmin = 3.5°
Absorption correction: analytical
(CrysAlis PRO; Rigaku OD, 2019)
h = 128
Tmin = 0.277, Tmax = 0.454k = 1312
2303 measured reflectionsl = 1214
708 independent reflections
Refinement top
Refinement on F2Hydrogen site location: difference Fourier map
Least-squares matrix: fullAll H-atom parameters refined
R[F2 > 2σ(F2)] = 0.015 w = 1/[σ2(Fo2) + (0.0188P)2]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.036(Δ/σ)max = 0.001
S = 1.04Δρmax = 0.50 e Å3
708 reflectionsΔρmin = 0.55 e Å3
25 parametersExtinction correction: SHELXL2018 (Sheldrick, 2015b), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
0 restraintsExtinction coefficient: 0.0043 (6)
Primary atom site location: structure-invariant direct methods
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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
Zn10.5000000.2500000.61168 (2)0.01163 (6)
Cl10.5000000.47954 (3)0.76915 (3)0.01375 (6)
N10.28237 (15)0.2500000.47949 (13)0.01603 (17)
H1A0.274 (3)0.3281 (19)0.416 (2)0.045 (4)*
H1B0.206 (5)0.2500000.533 (4)0.090 (11)*
Atomic displacement parameters (Å2) top
Zn10.01002 (9)0.01352 (9)0.01134 (9)0.0000.0000.000
Cl10.01288 (11)0.01346 (11)0.01490 (11)0.0000.0000.00253 (7)
N10.0136 (4)0.0211 (4)0.0134 (4)0.0000.0016 (3)0.000
Geometric parameters (Å, º) top
Zn1—Cl1i2.2722 (3)N1—H1Aii0.825 (17)
Zn1—Cl12.2722 (3)N1—H1A0.825 (17)
Zn1—N1i2.0155 (11)N1—H1B0.74 (4)
Zn1—N12.0155 (11)
Cl1i—Zn1—Cl1108.282 (14)Zn1—N1—H1Aii115.0 (13)
N1—Zn1—Cl1108.951 (17)Zn1—N1—H1A115.0 (13)
N1i—Zn1—Cl1i108.951 (17)Zn1—N1—H1B109 (3)
N1—Zn1—Cl1i108.951 (17)H1A—N1—H1Aii99 (2)
N1i—Zn1—Cl1108.950 (17)H1A—N1—H1B109 (2)
N1i—Zn1—N1112.66 (7)H1B—N1—H1Aii109 (2)
Symmetry codes: (i) x+1, y+1/2, z; (ii) x, y+1/2, z.
Hydrogen-bond geometry (Å, º) top
N1—H1A···Cl1iii0.825 (17)2.806 (18)3.4552 (9)137.0 (17)
N1—H1A···Cl1iv0.825 (17)2.897 (18)3.5505 (9)137.6 (16)
N1—H1B···Cl1v0.74 (4)2.95 (3)3.5556 (10)141 (1)
N1—H1B···Cl1vi0.74 (4)2.95 (3)3.5556 (10)141 (1)
Symmetry codes: (iii) x+1, y+1, z+1; (iv) x+1/2, y+1, z1/2; (v) x+1/2, y+1/2, z+3/2; (vi) x1/2, y, z+3/2.


DWB is grateful to the help of Dr Rosario Scopelliti in ISIC of EPFL. We would like to express our great appreciation to Professor László Forró in LPMC of EPFL for the fruitful discussions and support.

Funding information

Funding for this research was provided by: Swiss National Science Foundation (SNF) Sinergia network "NanoSkyrmionics" (grant No. CRSII5-171003).


First citationBrandenburg, K. (2006). DIAMOND. Crystal Impact GbR, Bonn, Germany.  Google Scholar
First citationClark, S., Latz, A. & Horstmann, B. (2017). ChemSusChem, 10, 4735–4747.  CrossRef CAS PubMed Google Scholar
First citationGardner, P. J., Pang, P. & Preston, S. (1989). Thermochim. Acta, 138, 371–374.  CrossRef CAS Google Scholar
First citationMacGillavry, C. H. & Bijvoet, J. M. (1936). Z. Kristallogr. 94, 249–255.  CAS Google Scholar
First citationRigaku OD (2019). CrysAlis PRO. Rigaku Oxford Diffraction, Yarnton, England.  Google Scholar
First citationSheldrick, G. M. (2015a). Acta Cryst. A71, 3–8.  Web of Science CrossRef IUCr Journals Google Scholar
First citationSheldrick, G. M. (2015b). Acta Cryst. C71, 3–8.  Web of Science CrossRef IUCr Journals Google Scholar
First citationWestrip, S. P. (2010). J. Appl. Cryst. 43, 920–925.  Web of Science CrossRef CAS IUCr Journals Google Scholar
First citationYamaguchi, T. & Lindqvist, O. (1981). Acta Chem. Scand. 35, 727–728.  CrossRef Google Scholar

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ISSN: 2056-9890
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