Assembly of Protonated Tetramethylpyrazine (TMP) in Triiodide. Vibrational Spectra and DFT Simulations

摘要

In the complex of tetramethylpyrazine (TMP) with HI3 two protonated molecules of TMP form the assembly of composition (TMP·H~+)2TMP(I_3~-)_2. The X-ray structure, determined at 100 K, shows the ~N-H…N hydrogen bonds markedly shorter than those found previously [13] at room temperature (2.828 vs. 2.894 A). The DFT calculations for isolated cation yield the value of 3.038 A that reflects the softness of the hydrogen bond potential. The calculations of vibrational frequencies for crystalline state reflect very well the IR spectra. This relates particularly to the v(NH ) mode. A remarkable discrepancy is observed when calculations are performed for isolated assemblies.