Experimental and DFT investigation of structure and IR spectra of H-bonded associates of p-(3-carboxy-1-adamantyl)thiacalix[4]arene

The IR spectra of p -(3-carboxy-1-adamantyl)thiacalix[4]arene ( 1 - AdCOOHTC4A ) have been studied. IR spectra of crystalline 1 - AdCOOHTC4A obtained at room temperature or upon heating to 250 °C or its dilute solutions lack bands of free hydroxyl groups. The frequency of hydroxyl groups at 3377 cm −1 indicates the formation of an intramolecular H-bond along the lower rim of the 1 - AdCOOHTC4A molecule. On the top edge of thiacalixarene, the carboxyl groups form dimeric or cyclic tetrameric complexes via intermolecular H-bonds. The conformation of the cone persists, but there is a mutual influence of H-bonds along the upper and lower rims of the thiacalix[4]arene molecule. The structure with dimer H-bonds between carboxyl groups is 31.9 KJ/mol less preferable than the conformation with tetramer cyclic H-bonds for 1-AdCOOHTC4A . Comparison of the absorption band of νOH alcohol hydroxyl groups in the IR spectra of 1 - AdCOOHTC4A at 3377 cm −1 , with the corresponding band of 1-AdTC4A at 3372 cm −1 , suggests that the presence of the second system of H-bonds of carboxyl groups in the first molecule does not affect the H-bond of alcohol hydroxyl groups. Graphical abstract