[N(CH3)3H]2CuCl4: Ab initio calculations and characterization of phase transitions by Raman spectroscopy

Abstract The X-ray powder diffraction pattern shows that at room temperature, [N(CH 3 ) 3 H] 2 CuCl 4 is crystallized in the monoclinic system with P2 1 /c space group. The phase transitions at T 1  ≈ 292/298 K, T 2  ≈ 262/264 K and T 3  ≈ 241 Khave been confirmed by the differential scanning calorimetry (DSC). Besides, the different phases have been studied by Raman scattering on single crystals, in the frequency range of 60–350 cm −1 . The infrared and Raman spectra are attributed on the basis of ab initio calculations of the vibrational spectra. The optimized geometries, calculated vibrational frequencies, infrared intensities and Raman activities of [CuCl 4 ] 2− and [N(CH 3 ) 3 H] + were calculated using the Hartree-Fock (HF) and density functional theory (B3LYP) with 3-21G, 6-31G(d) and 6-311G(d,p)basis sets. The temperature evolution of Raman spectra reveals the existence of phase transitions at T 1 , T 2 and T 3 and confirms their nature.