Hetmańczyk Joanna, Hetmańczyk Łukasz, Migdał-Mikuli Anna, Mikuli Edward
Faculty of Chemistry, Jagiellonian University, ul. Ingardena 3, 30-060 Kraków, Poland; Frank Laboratory of Neutron Physics, JINR, 141980 Dubna, Russia.
Faculty of Chemistry, Jagiellonian University, ul. Ingardena 3, 30-060 Kraków, Poland; Frank Laboratory of Neutron Physics, JINR, 141980 Dubna, Russia.
Spectrochim Acta A Mol Biomol Spectrosc. 2015 Feb 5;136 Pt C:1515-22. doi: 10.1016/j.saa.2014.10.044. Epub 2014 Oct 24.
The vibrational and reorientational motions of NH3 ligands and ClO4(-) anions were investigated by Fourier transform middle-infrared spectroscopy (FT-IR) in the high- and low-temperature phases of Mn(NH3)62. The temperature dependencies of full width at half maximum (FWHM) of the infrared bands at: 591 and 3385cm(-1), associated with: ρr(NH3) and νas(N-H) modes, respectively, indicate that there exist fast (correlation times τR≈10(-12)-10(-13)s) reorientational motions of NH3 ligands, with a mean values of activation energies: 7.8 and 4.5kJmol(-1), in the phase I and II, respectively. These reorientational motions of NH3 ligands are only slightly disturbed in the phase transition region and do not significantly contribute to the phase transition mechanism. Fourier transform far-infrared and middle-infrared spectra with decreasing of temperature indicated characteristic changes at the vicinity of PT at TC(c)=137.6K (on cooling), which suggested lowering of the crystal structure symmetry. Infrared spectra of Mn(NH3)62 were recorded and interpreted by comparison with respective theoretical spectra calculated using DFT method (B3LYP functional, LANL2DZ ECP basis set (on Mn atom) and 6-311+G(d,p) basis set (on H, N, Cl, O atoms) for the isolated equilibrium two models (Model 1 - separate isolated Mn(NH3)6 cation and ClO4(-) anion and Model 2 - [Mn(NH3)6(ClO4)2] complex system). Calculated optical spectra show a good agreement with the experimental infrared spectra (FT-FIR and FT-MIR) for the both models.
通过傅里叶变换中红外光谱（FT-IR）研究了Mn(NH₃)₆₂在高温和低温相时NH₃配体及ClO₄⁻阴离子的振动和重取向运动。在591和3385cm⁻¹处红外谱带的半高宽（FWHM）的温度依赖性，分别与ρr(NH₃)和νas(N-H)模式相关，表明NH₃配体存在快速（相关时间τR≈10⁻¹² - 10⁻¹³s）的重取向运动，在I相和II相中的平均活化能分别为7.8和4.5kJmol⁻¹。NH₃配体的这些重取向运动在相变区域仅受到轻微干扰，对相变机制没有显著贡献。随着温度降低的傅里叶变换远红外和中红外光谱表明，在TC(c)=137.6K（冷却时）的相变附近有特征变化，这表明晶体结构对称性降低。记录了Mn(NH₃)₆₂的红外光谱，并通过与使用DFT方法（B3LYP泛函、LANL2DZ有效核势基组（用于Mn原子）和6 - 311 + G(d,p)基组（用于H、N、Cl、O原子））计算的各自理论光谱进行比较来解释，用于两个孤立平衡模型（模型1 - 单独的孤立[Mn(NH₃)₆]²⁺阳离子和ClO₄⁻阴离子，模型2 - [Mn(NH₃)₆(ClO₄)₂]复合体系）。计算得到的光谱与两个模型的实验红外光谱（FT - FIR和FT - MIR）显示出良好的一致性。
