Cocrystals of Kemp's triacid. Part I: Molecular structure of 2:2 complex of 1,5,7-triazabicyclo[4.4.0]dec-5-ene with Kemp's triacid

The 2:2 hydrogen-bonded cocrystals between Kemp's triacid (KTA) and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) have been prepared and characterized by X-ray diffraction and FT-IR spectroscopy. Cocrystals of KTA-TBD (2:2) belong to the monoclinic system and its space group is P21/n with a = 12.3016(7) Å, b = 11.8130(6) Å, c = 14.3279(7) Å, β = 101.15(1)° and Z = 4. The KTA mono anion ring has a chair conformation with all three carboxylic groups in the axial positions and all three CH3 groups in the equatorial positions. In the crystal of the complex the cooperative systems involving inter- and intra-molecular hydrogen bonds are formed. In the solid state two protonated TBD molecules and two deprotonated KTA molecules form a dimer in which three-dimensional hydrogen-bonded networks have been found. The nature of these hydrogen bonds is well reflected by the proton vibrations in the FT-IR spectra of the crystal studied. The negative ion mode ESI-MS spectrum of the cocrystal indicated the existence of a KTA monoanion. The fragmentation pathways of this anion are discussed.