Gossypol inclusion compound with pyrazine: crystal structure and thermal behavior

Single crystals of gossypol complex with pyrazine (1:4) have been obtained in two ways: (I) in the pyrazine solution of gossypol (T = 56 °C) and (II) in the dichloromethane solution of dianhydrogossypol/pyrazine mixture (room temperature). The crystals were characterized by X-ray crystallography. Crystal data: (I), C30H30O8·4(C4H4N2), M = 838.91, T = 130 (2) K, MoKα = 0.71073 Å, a = 7.5230 (3), b = 13.9185 (6), c = 19.8328 (8) Å, α = 88.789 (4), β = 87.255 (3), γ = 86.683 (4)°, V = 2070.46 (15) Å3, Z = 2, Dcalc = 1.346 g/cm3, crystal system: triclinic, space group: P−1, R = 0.0393 for 7218 observed reflections; (II), C30H29,56O7,85·4(C4H4N2), M = 836.11, T = 100 (2) K, CuKα, 1.54184 Å, a = 7.5010 (4), b = 13.9425 (6), c = 19.7848 (9) Å, α = 88.618 (4), β = 87.442 (4), γ = 86.898 (4)°, V = 2063.57 (17) Å3, Z = 2, Dcalc = 1.345 g/cm3, crystal system: triclinic, space group: P−1, R = 0.0509 for 7215 observed reflections. Pair of gossypol and pyrazine molecules are formed the centrosymmetric tetramers untypical for gossypol type structures. Crystal structures are characterized with the presence of wide channels for guest molecules. TG-DSC curves of gossypol with pyrazine complex (1:4) showed that decomposition of crystals occurs in four steps. Formation of new gossypol:pyrazine host:guest complexes with ratios of 2:3 and 1:1 were observed in TG-DSC curves.