X-ray,FT-IR,ESI MS and PM5 studies of Schiff base of gossypol with allylamine and its complexes with alkali metal cations and perchlorate anion

Crystals of the Schiff base derivative of gossypol with allylamine (GSBAL) were grown and subsequently examined by X-ray diffraction and FT-IR methods. The crystal space group is C2/c with a = 16.057(1) Å, b = 14.112(1) Å, c = 27.185(2) Å, β = 99.371(5)? and Z  = 8. In the crystal, GSBAL exists in the enamine–enamine tautomeric form. The FT-IR spectral features of the crystals are in agreement with the X-ray data indicating that both parts of the molecule are similarly intramolecular hydrogen-bonded but different intermolecular hydrogen-bonded, although the molecule is symmetrically substituted. On the basis of the electrospray ionization mass spectrometry (ESI MS) experiments, it has been shown for the first time that Schiff base of gossypol forms complexes with the perchlorate anion and metal cations simultaneously. The ESI MS spectra of the 1:1:1 mixtures of GSBAL:GOS:M⁺, in the positive and negative ion detection mode, have indicated the preferential formation of the 1:1 complexes of GSBAL with M⁺ (Li, Na or K) and ClO₄ ^? over the respective complexes forming between GOS and the metal cation or the anion. The PM5 semiempirical calculations have allowed visualization of the most energetically favourable structures of these two types of GSBAL complexes.