Elsevier

Journal of Molecular Structure

Volume 1108, 15 March 2016, Pages 223-234
Journal of Molecular Structure

Crystal structure, spectroscopy, DFT studies and thermal characterization of Cobalt(II) complex with 2-protonated aminopyridinium cation as ligand

https://doi.org/10.1016/j.molstruc.2015.12.025Get rights and content

Highlights

  • A novel cluster (2-HAMP)2[CoBr4] has been synthesized and fully characterized.

  • The compound was characterized by X-ray, IR, Raman, TG-DTA techniques.

  • Theoretical study was attempted by the Density Functional Theory.

  • Charge transfer characteristics were examined by HOMO–LUMO.

  • High temperature phase transitions were characterized by X-ray powder diffraction as a function of temperature.

Abstract

Single crystals of a new organic–inorganic hybrid compound (2-HAMP)2[CoBr4], (2-HAMP = 2-protonated aminopyridinium cation) was synthesized and characterized by X-Ray diffraction at room temperature, DTA–TG measurement, FT-IR and FT-Raman spectroscopies and optical absorption. Its crystal structure is a packing of alternated organic and inorganic layers parallel to (a, b) plane. The different components are connected by a network of N/C–H⋯Br hydrogen bonds and halogen⋯halogen interactions. These hydrogen bonds give notable vibrational effects. Theoretical calculations were performed using density functional theory (DFT) for studying the molecular structure, vibrational spectra and optical properties of the investigated molecule in the ground state. The optimized geometrical parameters obtained by DFT calculations are in good agreement with single crystal XRD data. The energy and oscillator strength calculated by Time-Dependent Density Functional Theory (TD-DFT) results complements with the experimental findings. The simulated spectra satisfactorily coincide with the experimental UV–Visible spectrum. The results show good consistent with the experiment and confirm the contribution of metal orbital to the HOMO–LUMO boundary. Thermal analysis studies indicate the presence of three phase transitions at 68, 125 and 172 °C, which are confirmed by X-ray powder diffraction as a function of temperature.

Introduction

A great deal of interest has arisen in the synthesis of hybrid materials as a result of their special functional properties such as magnetic or ferroelectric transitions, conductivity, electroluminescence and photoluminescence [1], [2], [3], [4], [5], [6]. Furthermore, mixed organic-inorganic salts with the general formula A2MX4 (A: organic cation, M: transition metal and X: halogen = Cl, Br, I) have attracted considerable interest due to their multiple phase transitions related to the dynamics of the organic cations and inorganic anions. Interest in these compounds is rapidly increasing, as some of them exhibit interesting structural and physical properties like ferro-electricity, ferro-elasticity and low dimensional magnetism [7], [8], [9], [10], [11], [12], [13], [14], [15], [16]. The current attention, herein, is the incorporation of metal halide systems and organic cations as counter-ions in the extremely interesting hybrid materials and this strategy is expected to affect their appealing structural, optical and photoluminescence properties, which should lead to new interesting functional compounds. The present work deals with the synthesis and the characterizations of a novel hybrid compound, (2-HAMP)2[CoBr4], with an organic layer of 2-aminopyridine (C5H6N2), single X-ray diffraction study and detailed vibrational spectral analysis aided by Density Functional Theory (DFT) calculations. In the light of the theoretical calculations, correlation between FT-IR and FT-Raman spectra and computed results help unambiguous identification of vibrational modes and provide deeper insight into the bonding and structural features of the title compound. An optical absorption measurement and thermal studies were also performed.

Section snippets

Materials

All materials used in this work were of reagent grade purity and were used as commercially obtained: CoBr2·xH2O (99%, SIGMA ALDRICH), 2-aminopyridine (C5H6N2) (98%, SIGMA ALDRICH) and Hydrobromic Acid HBr (48%, SIGMA ALDRICH). Distilled water was used in this synthesis.

Synthesis of (2-HAMP)2[CoBr4]

A mixture of CoBr2·xH2O (0.218 g), 2-aminopyridine (C5H6N2) (0.094 g) and HBr (0.080 g) in the mole ratio 1:1:1 was heated for 34 h at 120 °C. The reaction was conducted in 23 ml poly(fluoroethylene-propylene) lined pressure

Crystal structure of (2-HAMP)2[CoBr4]

The present compound crystallizes in the monoclinic C2/c space group with four formula units in unit cell (Z = 4) with the following lattice parameters: a = 8.339(4) Å, b = 14.913(4) Å, c = 13.637(5) Å and β = 95.964(3)°. A summary of the key crystallographic informations for the title compound was quoted in Table 1. Selected experimental and calculated bond distances and angles, with a relative error for each one, are illustrated in Table 2. We find an average relative error of almost 3.4% for

Conclusion

The present work is devoted to the synthesis, X-ray characterization, spectroscopic properties and thermal analysis of (C5H7N2)2[CoBr4]. The structural and vibrational spectra calculated by DFT/B3LYP/LanL2DZ level of theory agree satisfactory with the experimental results. On the basis of agreement between experimental and theoretical results, assignments of all observed bands were examined and proposed in this investigation. The optical properties were conducted by absorption measurements

Conflicts of interest

The authors declare no competing financial interest.

Acknowledgements

The authors are grateful to Pr. Abdelmottaleb OUEDERNI for his assistance in TGA/DTA measurements of this study (The Unit of Joint Service of Research–National School of Engineers of Gabes, University of Gabes, Tunisia).

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