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Structural analysis and IR-spectroscopy of a new anilinium hydrogenselenite hybrid compound: A subtle structural phase transition

Abstract : An interesting structural behavior has been detected and characterized in a new anilinium based compound by single crystal X-ray diffraction measurements and infrared spectroscopy. The temperature dependent structural investigation reveals that the studied compound undergoes a subtle non-centrosymmetric to centrosymmetric structural phase transition. At room temperature the crystal structure is non-centrosymmetric and is characterized by an important disorder in the organic part where the independent aromatic rings are rotated around the C1-C4 and C7-C10 molecular axis by 52.06(6)degrees and 56.25(4)degrees respectively. By decreasing the temperature to 100 K the organic cation is less disordered and the rotation angle of the aromatic rings changes to 54.73(2)degrees. As a consequence, the low temperature structure becomes centrosymmetric. The infrared spectra recorded on cooling and heating the sample in the temperature range of 300-9 K support this analysis. The ammonium group (NH3) is significantly affected by the temperature change. This effect results, when cooling the sample below 140 K, in the appearance of a new vibrational band corresponding to the (NH3)-wagging modes at 705 cm(-1). The phenomenon is completely reversible and the new vibrational band disappears upon heating the sample above 140 K. Moreover, the m(C-N)-stretching and the (NH3)-scissoring modes are also affected by the temperature variation as can be seen in the spectral ranges of 1250-1400 cm(-1) and 1610-1635 cm(-1) respectively. The spectroscopic results are complementary to the structural analysis and indicate that the structural phase transition is correlated with the molecular rotation of the aromatic moieties around the C1-C4 axis that affect the different vibrational modes of the ammonium group.
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Submitted on : Friday, June 2, 2017 - 3:03:08 PM
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Radhwane Takouachet, Rim Benali-Cherif, El-Eulmi Bendeif, Nourredine Benali-Cherif, Sébastien Pillet, et al.. Structural analysis and IR-spectroscopy of a new anilinium hydrogenselenite hybrid compound: A subtle structural phase transition. Inorganica Chimica Acta, Elsevier, 2016, 446, pp.6-12. ⟨10.1016/j.ica.2016.02.047⟩. ⟨hal-01532136⟩



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