Preparation and Characterization of bis ( 4-methoxyanilinium ) tetrachlorozincate

*Corresponding author: wajda_sta@yahoo.fr ABSTRACT A new zinc complex of formula [C7H10NO]2 ZnCl4 has been prepared and characterized by X-ray diffraction, IR and UV-Visible spectroscopies. The complex crystallizes in the monoclinic space group P21/n with a minimal tetrahedral distortion of the ZnCl4 2ion and with lattice parameters: a =12.054 (2) Å, b =7.129 (3) Å, c =23.480 (2) Å, β = 100.67 (2)°, V = 1983.03 (1) Å 3 and Z = 4. The crystal structure was solved and refined to R = 0.080 and RW = 0.227 with 9611 independent reflections. It can be described by organic layers of p-anisidinium cations held together by C-H...O hydrogen bonds parallel to (010) plane, linked to the inorganic groups of ZnCl4 2anions through N-H...Cl hydrogen bonds, electrostatic and Van Der Waals interactions, to form a three-dimensional network.


INTRODUCTION
Organic-inorganic hybrid materials have gained enormous attention in recent years due to their interesting crystal structure and some special properties such as magnetic, optical, electrical and catalytic activity [1]. A recent advance in this field is to design the coordination frameworks of tetrahalometallates by the incorporation of various organic cations giving new structures with interesting applications [2]. Self-assembly process of such hybrid materials in solid state arises due to the variety of interactions including ionic interactions, hydrogen and halogen bondings and Van Der Waals interactions [3]. In the present investigation, we report the synthesis and crystal structure of a new organic-inorganic hybrid zinc complex, [C7H10NO]2 ZnCl4. Characterization of this material by IR and UV-Visible spectroscopies is also reported.

Material Preparation
The title compound was prepared in a Petri dish by slow evaporation of an ethanolic solution of 4-methoxyaniline (2 mmol), zinc chloride (1 mmol) and diluted hydrochloric acid (10 mL, 1M) at room temperature. The crystals remained stable under normal conditions of temperature and humidity. The chemical formula was determined by X-ray crystal structure analysis.

Physical measurement
The unit -cell dimensions were refined using X-ray diffraction data collected with a Mach 3 Enraf Noninus diffractometor using Ag Kα radiation. Crystal data, parameters used for diffraction data collection and strategy used for the crystal structure determination and their results, are listed in Table 1. The atomic coordinates and equivalent isotropic displacements are shown in Table 2.
IR spectra were recorded using KBr pellets in the range of 4000-400 cm -1 on a Nicolet IR200 FT-IR Spectrometer at ambient temperature.
Electronic spectra absorptions were made on a Perkin-Elmer Lambda UV-Visible spectrophotometer for 2.10 -3 M solution of [C7H10NO]2 ZnCl4 in absolute ethanol solvent.

X-ray diffraction analysis
The asymmetric unit of the title compound ( Fig.1) contains two p-anisidinium cations and one tetrachlorozincate anion. The crystal structure consists of organic layers of p-anisidinium cations, parallel to the (b,c) plane, held together by C-H…O hydrogen bonds. These layers are attached to the inorganic groups of ZnCl4 2anions through N-H…Cl hydrogen bonds, electrostatic and Van Der Waals interactions, to form a three-dimensional infinite network (Fig.2). J u l y 0 8 , 2 0 1 4   As shown in Fig.3, in the crystal structure of the title complex, ZnCl4 2groups are connected by hydrogen bonds N-H…Cl. The organic and inorganic species interact by mean of seven N-H…Cl hydrogen bonds (Table 3), giving rise to a porous layer. The corresponding N…Cl distances vary between 3.173(4) and 3.413(4) Å, which can be considered relatively weak [4]. In the organic layer, there are no π-π interactions between the 4-methoxyanilinium cations, between which there is a face-to-face distance of 4Å which is longer than values observed in similar compounds [5].

. Projection of a layer of the structure of [C7H10NO]2 ZnCl4 along the a direction
The zinc atom is tetrahedrally coordinated by chlorine atoms, with Zn-Cl distances ranging from 2.234(1) to 2.288(1)Å and Cl-Zn-Cl angles varying from 105.76(5) to 113.32 (5)° (Table 4).These values show a slight distortion of the ZnCl4 2tetrahedra, which can be explained by the involving of the chlorine ions in the hydrogen bonding. These results are in agreement with those found in anilinium tetrachlorozincate [6]. The organic molecule exhibits a regular spatial configuration with normal distances C-C, C-N and angles C-C-C, C-C-N ( Table 5). The mean value of the C-C length of the C6-ring is 1.4038Å, which is between single and double bonds and agrees with that observed in the C6-ring of benzene derivatives [7]. All the carbon atoms of the C6-ring are coplanar and they form conjugated planes with average deviation of ±0.042Å and ±0.079Å, and they form between them a dihedral angle of 7.45°. J u l y 0 8 , 2 0 1 4

Infrared Spectroscopy
The IR vibrational frequencies of the free 4-methoxyaniline have been taken for band assignments and to verify the shift in their frequencies with the present compound [9][10].

UV Absorption and Diffuse Reflectance
The optical absorption spectrum of [C7H10NO]2 ZnCl4 was measured in the range 200-800 nm and the spectrum is shown in Fig.5.
In figure 5, we observe two strong absorption bands at 276 and 282 nm due to the π π* transitions. The spectrum shows also a broad weak band around 306 nm which can be attributed to the n π* transition.
As the direct band gap [C7H10NO]2 ZnCl4 has an absorption coefficient (α) obeying the relation for high photon energies (hν): (11) where Eg is the band gap energy of the crystal and A is a constant.
The plot of variation of ( ) 2 vs. is shown in Fig.6. The band gap energy is found to be 4.26 eV. This value suggests that the studied compound could be used for optical applications in far UV region [12] as well as for dielectric properties [13].

Conclusion
A new hybrid material, [C7H10NO]2 ZnCl4, has been prepared. Its atomic arrangement is described by organic layers of 4-methoxyanilinium cations attached to the inorganic groups of ZnCl4 2anions through N-H…Cl hydrogen bonds as to form a three-dimensional network. The UV-Vis spectral analyses reveal that the crystal can be used as dielectric with a band gap energy of 4.26 eV.