International Journal of Inorganic ChemistryVolume 2011 (2011), Article ID 274073, 7 pagesdoi:10.1155/2011/274073

Research Article

Synthesis and Characterization of Bis(4-methylbenzylammonium) Tetrachloridocadmate(II)

R. Kefi,¹ M. Zeller,² F. Lefebvre,³ and C. Ben Nasr¹

¹Laboratoire de Chimie des Matériaux, Faculté des Sciences de Bizerte, Zarzouna 7021, Tunisia²Department of Chemistry, Youngstown State University, One University Plaza, Youngstown, OH 44555-3663, USA³Laboratoire de Chimie Organometallique de Surface (LCOMS), Ecole Supérieure de Chimie Physique Electronique, 69622 Villeurbanne Cedex, France

Received 11 November 2011; Accepted 13 December 2011

Academic Editor: Alexander Steiner

Copyright © 2011 R. Kefi et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

The crystal structure of the new inorganic-organic hybrid compound [4-CH₃C₆H₄CH₂NH₃]₂[CdCl₄] has been determined by single crystal X-ray diffraction. The compound crystallizes in the orthorhombic space group Pnma with lattice parameters , ,  Å, ,  Å³, and . The framework of the title compound is built upon layers parallel to (010) made up from corner-sharing CdCl₆ octahedra. 4-Methylbenzylammonium cations are situated between the layers and connect them via an N–H⋯Cl hydrogen bonding network. The Cd atom is located on an inversion centre, and the coordination environment is described as distorted octahedral. Solid state ¹³C CP-MAS NMR spectroscopy is in agreement with the X-ray structure. DFT calculations allow the attribution of the carbon peaks to the independent crystallographic sites. Thermal analysis and infrared spectroscopy were also used to characterize the complex.

1. Introduction

In recent years, a great effort has been devoted to the self-assembly of organic and inorganic molecules in the solid state, because it allows to design new solids with specific properties, such as electronic, optical, thermal, and catalytic [1, 2]. Among these materials, chlorocadmate compounds have been of special interest for their structural flexibility. Complexes with Cd(II) centers have been at the center of growing interest due to their variable frameworks, and their potential photoluminescent and nonlinear optical (NLO) properties [3, 4]. They can occur as simple tetrahedral anions CdX₄²⁻ or form the backbone of chain polymers. This is due to the fact that the Cd²⁺ ion, being a d10 transition metal ion, exhibits a great variety of coordination numbers and geometries, depending on crystal packing and hydrogen bonding, as well as halide dimensions [5–10]. A wide variety of stoichiometries that belong to this class of compounds makes the crystal chemistry of chlorocadmates extremely diverse and complex. Common features of all these compounds are the invariable presence of octahedral (CdCl₆) units in the anhydrous species. A network of hydrogen bonding, involving organic cations, generally connects the inorganic anions together and stabilizes the whole crystal structure [11–14]. Therefore, the Cd(II) salt is suitable for the assembly of coordination frameworks.

As a part of our ongoing investigations in molecular salts containing metal-chlorido complexes [15, 16], we present here the crystal structure of one such compound, [4-CH₃C₆H₄CH₂NH₃]₂[CdCl₄].

2. Experimental

2.1. Chemical Preparation

4-Methybenzylamine (2 mmol, 0.242 g) and CdCl₂ (1 mmol, 0.183 g) were dissolved in dilute HCl (10 mL, 1 M), and the resultant solution was slowly evaporated at room temperature. A crystal of the title compound, which remained stable under normal conditions of temperature and humidity, was isolated after several days and subjected to X-ray diffraction analysis (yield 56%). Element analysis calculated: C 38.51, H 4.81, N 5.61%; found: C 38.46, H 4.67, N 5.78%.

2.2. Investigation Techniques

The characterization of these salts was carried out using X-ray diffraction, solid state NMR spectroscopy, DFT calculations, infrared spectroscopy, and thermal analysis (differential thermal analysis, DTA, and thermal gravimetric analysis, TGA).

2.2.1. X-Ray Diffraction

A single crystal was carefully selected under a microscope in order to perform its structural analysis by X-ray diffraction. The intensity data were collected on a Bruker AXS SMART APEX CCD diffractometer using the omega scan technique with MoKα radiation (λ = 0.7107 Å). The structure was solved with direct methods using SHELXS-97 [17] and refined with full-matrix least-squares techniques using SHELXTL-6.14 [18]. The drawings were made with Diamond [19]. Crystal data and experimental parameters used for the intensity data collection are summarized in Table 1.

Table 1: Cristallographic data and refinement details of the title compound.

CdCl₄·(C₈H₁₂N)₂
F(000) = 1000.00

= 498.57
= 1.706 Mg m⁻³

Orthorhombic, Pnma
Mo Kα radiation, λ = 0.71073 Å

a = 10.721 (2) Å
Cell parameters from 670 reflections

b = 33.986 (6) Å
θ = 2.4–31.3°

c = 5.326(1) Å
μ = 1.68 cm⁻¹

β = 97.222 (1)°
T = 289 K

V = 1940.8(7) Å³
Crystal size: 0.009 × 0.08 × 0.06 mm

Z = 4
2856 independent reflections

φ and ω scans
2278 reflections with

= 0.608, = 0.746
= 0.023

Color: colourless
= 30.1°, = 3.6°

Goodness-of-fit on  : 1.1

6959 measured reflections

Refinement on

= 0.041
where

wR(F²) = 0.093
(Δ/σ)max = 0.001

11674 reflections
Δρ max = 1.23 e Å⁻³

111 parameters
Δρ min = −1.78 e Å⁻³

Crystals of the title compound were also analyzed at lower temperature (100 K). At this temperature the diffraction patterns exhibit pronounced “streaks” of intensity between rows of well defined Bragg peaks, indicating modulation of the structure and disorder of molecular entities with repeating patterns that are not a multiple of the basic unit cell as defined by the main Bragg peaks. Integration of only the Bragg peaks under omission of the streaks confirmed this. The average structure thus obtained shows substantial disorder of some of the chlorine atoms, with ratios refining to an 82 : 18 ratio. It can be imagined that the positions of the Cl atoms in neighboring layers of Cd and Cl are in some way related, but not in a way that repeats itself within the dimensions given by the unit cells, thus causing the non-Bragg like behavior at 100 K. No attempts were made to completely analyze the non-Bragg low temperature phase of the compound.

2.2.2. NMR Spectroscopy

The ¹³C NMR spectrum was recorded on a solid-state high-resolution Bruker DSX-300 spectrometer operating at 75.49 MHz with a classical 4 mm probehead allowing spinning rates up to 10 kHz. The chemical shifts are given relative to tetramethylsilane (external reference, precision 0.5 ppm). The spectrum was recorded by use of cross-polarization (CP) from protons (contact time 5 ms) and MAS. Before recording the spectrum, it was checked that there was a sufficient delay between the scans allowing a full relaxation of the protons. DFT calculations were undertaken in order to assign the NMR resonances to the different nonequivalent C atoms of the unit cell. These calculations were made at the B3LYP/6-31+G* level using the GAUSSIAN98 program [20].

2.2.3. IR Spectroscopy

The spectrum was recorded in the range 4000–400 cm⁻¹ with a “Perkin-Elmer FTIR” spectrophotometer 1000 using a sample dispersed in spectroscopically pure KBr pressed into a pellet.

2.2.4. Thermal Analysis

Thermal analysis was performed using the “multimodule 92 Setaram” analyzer operated between room temperature and 773 K with an average heating rate of 5 Kmin⁻¹.

3. Results and Discussion

3.1. X-Ray Diffraction Study

The main geometrical features of the different chemical entities of the organic-inorganic hybrid compound [4-CH₃C₆H₄CH₂NH₃]₂[CdCl₄] are reported in Tables 2, 3, and 4.

Table 2: Selected bond lengths (Å) in [4-CH₃C₆H₄CH₂NH₃]₂[CdCl₄].

Cd1–Cl2
2.5020 (11)
C5–C8
1.506 (6)

Cd1–Cl2i
2.5020 (11)
C2–C3
1.385 (6)

Cd1–Cl3
2.6557 (15)
C1–H1A
0.9700

Cd1–Cl1
2.6630 (14)
C1–H1B
0.9700

Cd1–Cl1ii
2.6676 (14)
C7–H7
0.9300

Cd1–Cl3iii
2.7089 (15)
C8–H8A
0.9600

Cl1–Cd1iv
2.6677 (14)
C8–H8B
0.9600

Cl3–Cd1v
2.7089 (15)
C8–H8C
0.9600

C1–N1
1.440 (6)
N1–H1C
0.8900

C1–C2
1.507 (6)
N1–H1D
0.8900

C3–C4
1.380 (6)
N1–H1E
0.8900

C4–C5
1.386 (6)
C6–H6
0.9300

C6–C7
1.378 (6)
C3–H3
0.9300

C2–C7
1.367 (6)
C4–H4
0.9300

C5–C60
1.388 (6)

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

Table 3: Selected bond angles (°) in [4-CH₃C₆H₄CH₂NH₃]₂[CdCl₄].

Cl2–Cd1–Cl2i
174.05 (7)
C2–C7–C6
121.8 (4)

Cl2–Cd1–Cl3
92.92 (3)
N1–C1–H1A
109.0

Cl2i –Cd1–Cl3
92.92 (3)
C2–C1–H1A
109.0

Cl2–Cd1–Cl1
90.87 (3)
N1–C1–H1B
109.0

Cl2i –Cd1–Cl1
90.87 (3)
C2–C1–H1B
109.0

Cl3–Cd1–Cl1
84.62 (5)
C5–C8–H8C
109.5

Cl2–Cd1–Cl1ii
89.36 (3)
C1–N1–H1C
109.5

Cl2i –Cd1–Cl1ii
89.35 (3)
C1–N1–H1D
109.5

Cl3–Cd1–Cl1ii
90.92 (5)
C4–C3–H3
119.6

Cl1–Cd1–Cl1ii
175.54 (7)
C2–C3–H3
119.6

Cl2–Cd1–Cl3iii
87.12 (3)
C3–C4–H4
119.5

Cl2i –Cd1–Cl3iii
87.12 (3)
C5–C4–H4
119.5

Cl3–Cd1–Cl3iii
177.204 (13)
C1–N1–H1E
109.5

Cl1–Cd1–Cl3iii
92.58 (5)
C7–C6–H6
119.8

Cl1ii –Cd1–Cl3iii
91.88 (5)
C5–C6–H6
119.8

Cd1–Cl1–Cd1iv
175.54 (7)
C2–C7–H7
119.1

Cd1–Cl3–Cd1v
176.50 (7)
C6–C7–H7
119.1

N1–C1–C2
113.1 (4)
C5–C8–H8A
109.5

C7–C2–C3
118.1 (4)
C5–C8–H8B
109.5

C7–C2–C1
121.0 (4)
H8A–C8–H8C
109.5

C3–C2–C1
120.9 (4)
H8A–C8–H8B
109.5

C4–C3–C2
120.8 (4)
H1A–C1–H1B
107.8

C3–C4–C5
121.0 (4)
H1C–N1–H1E
109.5

C4–C5–C6
117.9 (4)
H1D–N1–H1E
109.5

C4–C5–C8
121.2 (4)
H8B–C8–H8C
109.5

C6–C5–C8
120.9 (4)
H1C–N1–H1D
109.5

C7–C6–C5
120.5 (4)

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

Table 4: Hydrogen-bond geometry (Å, °) in [4-CH₃C₆H₄CH₂NH₃]₂[CdCl₄].

D–H⋯A
D–H
H⋯A
D⋯A
D–H⋯A

N1–H1C⋯Cl1
0.89
2.76
3.418 (4)
131

N1–H1D⋯Cl3vi
0.89
2.70
3.474 (4)
147

N1–H1D⋯Cl1vi
0.89
2.82
3.479 (4)
132

N1–H1E⋯Cl3iii
0.89
2.67
3.399 (4)
140

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

The asymmetric unit of the title compound (Figure 1) contains one 4-methylbenzylammonium and one half of a CdCl₂(Cl1/2)₄ fragment. Packing of [4-CH₃C₆H₄CH₂NH₃]₂[CdCl₄] viewed along the b-axis (Figure 2) shows a layer of corner sharing [CdCl₆] octahedra. The minimum Cd–Cd distance within a layer is 5.362(1) Å. In the structure, three symmetry independent chlorine atoms are observed (Cl1, Cl2, and Cl3), and only Cl1 and Cl3 form a bridge between two cadmium centers. In this way, the chlorine atoms form a distorted octahedron around each cadmium atom (Figure 3), giving the overall stoichiometry for the anions of [CdCl₂(Cl1/2)₄]²⁻. The Cd atom is located on an inversion centre. Table 2 shows that the symmetric bridging Cd–Cl distances are long, varying between 2.663(1) and 2.709(1) Å, while the terminal Cd–Cl distances are close to 2.502(1) Å, which is typical of six coordinated Cd(II) [18]. The Cl–Cd–Cl bond angles average exactly 90.0° and range between 84.62 (5)° for Cl3–Cd1–Cl1 and 92.92 (3) for Cl2–Cd1–Cl3 (Table 3), again confirming the close to symmetric octahedral nature of the CdCl₆ building units.

Figure 1: Asymmetric unit of [4-CH₃C₆H₄CH₂NH₃]₂[CdCl₄] with atom labels and 50% probability displacement ellipsoids for non-H atoms.

Figure 2: Projection of [4-CH₃C₆H₄CH₂NH₃]₂[CdCl₄] structure in the plane (a, c). The dotted lines indicate hydrogen bonds. A polyhedral representation is given for [CdCl₆].

Figure 3: Coordination geometry of Cd(II) ions in [4-CH₃C₆H₄CH₂NH₃]₂[CdCl₄]. Symmetry codes: (i) x, −y + 1/2, z; (ii) x, y, z − 1; (iii) x − 1/2, y, −z + 1/2.

In this structure, the 4-methylbenzylammonium cationic group compensates the negative charge of a half [CdCl₂(Cl1/2)₄]²⁻ anion leading to neutrality for the structure as a whole. Figure 4 shows CdCl₆ octahedra and the 4-methylbenzylammonium cations connected via hydrogen bonds N1–H1C⋯Cl1, N1–H1D⋯Cl3vi, N1–H1D⋯Cl1vi, and N1–H1E⋯Cl3iii, one of which is bifurcated N1–H1D⋯(Cl3vi, Cl1vi) (symmetry codes in Table 4). Only the bridging chlorine atoms Cl1 and Cl3 of the CdCl₆ octahedron participate in hydrogen bonding, while all hydrogen atoms that are attached to N1 are involved in hydrogen bondings. No π-π stacking interactions between neighboring aromatic rings or C–H⋯π interactions towards them are observed. The interlayer space is large enough to allow for only minimal distortions of the cation. The angles and atom distances of the cation have their usual values as reported for the related compound with the same cation, bis(4-methylbenzylammonium) tetrachlorozincate [21]. It is worth noting that as cadmium is found in the second period of the transition metals, it has more variable coordination numbers and geometries than zinc. This explains the difference of the architectures between the cadmium and zinc salts. Indeed, for the title compound, the CdCl₆ octahedra are sharing their common vertex of chlorine, while, in the Zn(II) salt [21], the ZnCl₄ tetrahedra are linked by hydrogen bonds.

Figure 4: Projection of [4-CH₃C₆H₄CH₂NH₃]₂[CdCl₄] structure along the -axis. The dotted lines indicate hydrogen bonds. A polyhedral representation is given for [CdCl₆].

3.1.1. NMR Spectroscopy

The ¹³C CP-MAS NMR spectrum of the title compound is shown on Figure 5. It displays two well-defined peaks in the resonance region of the aliphatic carbon atoms, at 22.2 and 44.3 ppm, showing that the asymmetric unit cell should contain only one organic molecule, which is in good agreement with the X-ray results (Figure 1). Theoretical calculations were then undertaken in order to assign the NMR resonances to the different crystallographically inequivalent carbon atoms of the unit cell. These calculations were made at the B3LYP/6-31+G* level. The different atoms were labeled as depicted below:

Figure 5: Experimental and simulated ¹³C CP-MAS NMR spectra of the studied compound.

Three different calculations were made on the organic cation, and, in all cases, the theoretical chemical shifts were subtracted from those of the reference (tetramethylsilane) calculated at the same level of theory:(1)calculation of the NMR chemical shifts (with the GIAO method) by taking the positions of atoms obtained by X-ray diffraction;(2)optimization of the positions of the protons in the above molecule and calculation of the NMR chemical shifts in this semioptimized geometry. Indeed, X-ray diffraction leads always to underestimated X–H bond lengths, due to the fact that it is sensitive to the electronic cloud and does not see the nuclei;(3)full optimization of all atoms and calculation of NMR chemical shifts. This calculation, compared to the above one, will give indications on the steric hindrance around the organic cation and on the positions where it is the strongest.

The results are listed in Table 5 which shows that there is a good agreement between the experimental and theoretical values calculated after optimization of the position of the protons, allowing unambiguously the attribution of the different NMR signals to the carbon atoms of the structure.

Table 5: Calculated and experimental ¹³C chemical shifts in the studied compound.

Atom
No optimization
Optimization of all atoms
Optimization of protons
Experimental

C1
122.8
134.9
128.9
130.0

C2
121.2
126.7
122.9
128.3

C3
125.8
134.9
131.9
130.0

C4
132
140.5
137.7
131.8

C5
156.9
159.8
155.7
137.4

C6
131.7
140.5
137.5
131.8

C7
27.4
59.9
45.2
44.3

C9
0.8
24
23.8
22.2

3.1.2. IR Spectroscopy

The IR spectrum of crystalline [4-CH₃C₆H₄CH₂NH₃]₂[CdCl₄] is shown in Figure 6. The most representative and characteristic vibrational modes of this compound can be compared to those of similar complexes [22]. Some aspects of the performed assignments are briefly commented as follows.(i)In the high-frequency region, the broad band between 3600 and 2500 cm⁻¹ corresponds to the valence vibrations of C‒H and N‒H groups [23].(ii)The observed bands in the 1620−1200 cm⁻¹ region can be attributed to the bending vibrations of N‒H groups and to the valence vibrations of C=C and C‒N groups [24].(iii)The bands between 1000 and 700 cm−1 are assigned to out of plane bending modes γ(Cary-H) and γ(Cary-C) [25].

Figure 6: IR absorption spectrum of [4-CH₃C₆H₄CH₂NH₃]₂[CdCl₄].

3.1.3. Thermal Analysis

Simultaneous TGA-DTA curves of the bis(4-methylbenzylammonium) tetrachlorido-cadmate(II) are given in Figure 7. The DTA curve shows that this compound undergoes a series of endothermic transformations in a wide temperature range (560–773 K). The most important one appears at about 565 K. It corresponds to the melting point, which is in good agreement with the result obtained by the capillarity tube method. The important weight loss observed in this temperature region is attributed to the degradation of the organic entity. A black residue is obtained at the end of the experiment.

Figure 7: DTA and TGA curves of [4-CH₃C₆H₄CH₂NH₃]₂[CdCl₄] at rising temperature.

Additional MaterialCrystallographic data for the title compound have been deposited at the Cambridge Crystallographic Data Center as supplementary publication (CCDC 852580). These data can be obtained free of charge at http://www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Center, 12, Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223/336 033; mailto: deposit@ccdc.cam.ac.uk).

4. Summary

The title compound was prepared as single crystals at room temperature and characterized by physicochemical methods. On the structural level, the atomic arrangement of this material consists of a network of [CdCl₂(Cl1/2)₄]²⁻ anions and 4-methylbenzylammonium cations connected by N−H⋯Cl hydrogen bonding interactions. The number of ¹³C CP-MAS-NMR components is in full agreement with the ones of crystallographically independent sites. Upon heating, this salt melts and the organic entities degrade.

References

N. Kimizuka and T. Kunitake, “Organic two-dimensional templates for the fabrication of inorganic nanostructures: organic/inorganic superlattices,” Advanced Materials, vol. 8, no. 1, pp. 89–91, 1996.

D. B. Mitzi, K. Chondroudis, and C. R. Kagan, “Organic-inorganic electronics,” IBM Journal of Research and Development, vol. 45, no. 1, pp. 29–45, 2001.

R. Wang, M. Hong, J. Luo, R. Cao, Q. Shi, and J. Weng, “Syntheses and crystal structures of five cadmium(II) complexes derived from 4-aminobenzoic acid,” European Journal of Inorganic Chemistry, no. 11, pp. 2904–2912, 2002.

H. Fleischer, “Structural chemistry of complexes of ()d¹⁰ns mm metal ions with β-N-donor substituted thiolate ligands (, 2),” Coordination Chemistry Reviews, vol. 249, no. 7-8, pp. 799–827, 2005.

L. J. Barbour, L. R. MacGillivray, and J. L. Atwood, “Structural consequences of M-Cl⋯H-N hydrogen bonds in substituted pyridinium salts of the cobalt(II)tetrachloride anion isolated from liquid clathrate media,” Supramolecular Chemistry, vol. 7, no. 2, pp. 167–169, 1996.

K. Müller-Dethlefs and P. Hobza, “Noncovalent interactions: a challenge for experiment and theory,” Chemical Reviews, vol. 100, no. 1, pp. 143–167, 2000.

F. H. Allen, V. J. Hoy, J. A. K. Howard et al., “Crystal engineering and correspondence between molecular and crystal structures. Are 2- and 3-aminophenols anomalous?” Journal of the American Chemical Society, vol. 119, no. 15, pp. 3477–3480, 1997.

G. Aullón, D. Bellamy, L. Brammer, E. A. Bruton, and A. G. Orpen, “Metal-bound chlorine often accepts hydrogen bonds,” Chemical Communications, no. 6, pp. 653–654, 1998.

G. R. Lewis and A. G. Orpen, “A metal-containing synthon for crystal engineering: synthesis of the hydrogen bond ribbon polymer [4,4′-H₂bipy][MCl₄] (M = Pd, Pt),” Chemical Communications, no. 17, pp. 1873–1874, 1998.

B. Dolling, A. L. Gillon, A. G. Orpen, J. Starbuck, and X. M. Wang, “Homologous families of chloride-rich 4,4′-bipyridinium salt structures,” Chemical Communications, no. 6, pp. 567–568, 2001.

L. P. Battaglia, A. Bonamartini Corradi, G. Pelosi et al., “Synthesis and characterization of layered chlorocadmates(II) with perovskite-like structures,” Chemistry of Materials, vol. 4, no. 4, pp. 813–818, 1992.

J. T. Veal and D. J. Hodgson, “The crystal and molecular structure of tris(ethylenediamine)cobalt(III) hexachlorocadmate(II) dichloride dihydrate, [Co(N₂C₂H₈)₃]₂[CdCl₆]Cl₂·2H₂O,” Inorganic Chemistry, vol. 11, no. 3, pp. 597–600, 1972.

A. B. Corradi, M. R. Cramarossa, and M. Saladini, “Design, synthesis, structural and thermal characterisation of polymeric chlorocadmate(II) compounds with one-dimensional inorganic chain structures,” Inorganica Chimica Acta, vol. 257, no. 1, pp. 19–26, 1997.

A. B. Corradi, A. M. Ferrari, and G. C. Pellacani, “Organic-inorganic composite materials: structural archetypes of linear polymeric chlorocadmates (II),” Inorganica Chimica Acta, vol. 272, no. 1-2, pp. 252–260, 1998.

M. E. Glaoui, E. Jeanneau, F. Lefebvre, and C. B. Nasr, “Synthesis and physicochemical studies of two new compounds C₇H₁₈N₂O TCl₄ (T = Cd, Cu),” Canadian Journal of Analytical Sciences and Spectroscopy, vol. 54, no. 2, pp. 70–82, 2009.

M. E. Glaoui, R. Kefi, E. Jeanneau, F. Lefebvre, and C. B. Nasr, “Structural, spectroscopic and thermal investigations of a new bis(5-chloro-2,4-dimethoxyanilinium) tetrachloridocadmate trihydrate,” Canadian Journal of Analytical Sciences and Spectroscopy, vol. 54, no. 1, pp. 1–10, 2009.

G. M. Sheldrick, SHELXS-97, A Program for Automatic Solution of Crystal Structure, University of Göttingen, Göttingen, Germany, 1997.

Bruker Advanced X-ray Solutions, SHELXTL (Version 6.14), Bruker AXS Inc., Madison, Wis, USA, 2003.

K. Brandenburg, Diamond Version 2.0 Impact, GbR, Bonn, Germany, 1998.

M. J. Frisch, et al., GAUSSIAN98, Gaussian Inc., Pittsburgh, Pa, USA, 1998.

R. Kefi, E. Jeanneau, F. Lefebvre, and C. Ben Nasr, “Bis(4-methylbenzylammonium) tetrachloridozincate: a new noncentrosymmetric structure characterized by 13C CP-MAS NMR spectroscopy,” Acta Crystallographica, vol. C67, pp. m126–m129, 2011.

I. B. Gharbia, A. Oueslati, C. B. Nasr, and F. Lefebvre, “Crystal structure and spectroscopic studies of 2-amino-3-methylpyridinium tetrachlorozincate monohydrate, [2-NH2-3-CH₃C₅H₃NH]₂ZnCl₄.H₂O,” Canadian Journal of Analytical Sciences and Spectroscopy, vol. 52, no. 1, pp. 32–45, 2007.

A. Oueslati, A. Rayes, C. Ben Nasr, and F. Lefebvre, “Synthesis and characterization of 2-amino-3-methylpyridinium dihydrogenomonoarsenate,” Materials Research Bulletin, vol. 40, no. 10, pp. 1680–1689, 2005.

J. Oueslati, A. Oueslati, F. Lefebvre, M. Rzaïgui M, and C. Ben Nasr, “Structural and Spectroscopic Studies of 3,5-diamino-4H-1,2,4-triazol-1-ium dihydrogenmonophosphate,” Canadian Journal of Analytical Sciences and Spectroscopy, vol. 53, p. 36, 2007.

R. Kefi, S. Abid, C. B. Nasr, and M. Rzaigui, “Synthesis and characterization of a new monophosphate (5-Cl-2,4-(OCH₃)₂C₆H₂NH₃)H₂PO₄,” Materials Research Bulletin, vol. 42, no. 3, pp. 404–412, 2007.