Structure and Vibrational Spectra of the 1:1 Squaric Acid(H2SQ)-Tetramethylpyrazine(TMP)Adduct

摘要

The crystal structure of the title complex was determined at 100 K by X-ray diffraction.It consists of double ionized dimeric(HSQ)+_2~(2+)species and protoned TMP centre dot H~+cations.Strong charge assisted(OHO)~-and(NHO)~+hydrogen bonds are the main factor of crystal packing.A wealth of unconventional C-H...O and C-H...N relatively short bridges should be emphasized.Particularly important are the latter ones binding two adjacent TMPH cations.The structure is well manifested in the IR and Raman spectra,particularly in the region of v(OH)and v(NH)as well as of v(C=O)frequencies.The complexation of TMP leads to a marked change in the low and high frequency vibrations of the methyl groups.An anomaly on the DSC runs has been found at 163/175 K(cooling/heating)which can be assigned to the freezing of the methyl group rotations.No change of the crystal symmetry is observed at this temperature.