GOSSYPOL CLATHRATES: STRUCTURE AND THERMAL BEHAVIOR OF GOSSYPOL SOLVATES WITH TWO PICOLINE ISOMERS
Gossypol forms stable solvates with 4- and 2-picolines at room temperature. The solvates are investigated by single crystal X-ray diffraction and thermal analysis. Solvate crystals of gossypol with 4-picoline (1) have the 1:3 composition (gossypol:4-picoline) and crystallize in the <i>P</i>2<sub>1</sub>/<i>с</i> space group. This substance is isostructural to a trisolvate of gossypol with pyridine. Solvate crystals of gossypol with 2-picoline (2) have the 1:4 composition (gossypol:2-picoline) and crystallize in the <i>P</i>-1 space group. The unit cell parameters for the investigated structures are as follows: 1 monoclinic crystals, C<sub>30</sub>H<sub>30</sub>O<sub>8</sub>·3C<sub>6</sub>H<sub>7</sub>N, <i>a</i> = 10.7530(1) Å, <i>b</i> = 20.7834(3) Å, <i>c</i> = 19.1166(2) Å, β = 95.537(1)°, <i>V</i> = 4252.32(9) Å<sup>3</sup>, <i>M</i> = 797.92, <i>Z</i> = 4, <i>d</i><sub>x</sub> = 1.246 g/cm<sup>3</sup>, and <i>R</i> = 0.0489 for 4102 reflections; 2 triclinic crystals, C<sub>30</sub>H<sub>30</sub>O<sub>8</sub>·4C<sub>6</sub>H<sub>7</sub>N, <i>a</i> = 11.467(1) Å, <i>b</i> = 14.962(2) Å, <i>c</i> = 15.570(3) Å, α = 75.62(1)°, β = 69.83(1)°, γ = 79.58(1)°, <i>V</i> = 2414.6(7) Å<sup>3</sup>, <i>M</i> = 891.04, <i>Z</i> = 2, <i>d</i><sub>x</sub> = 1.226 g/cm<sup>3</sup>, and <i>R</i> = 0.0528 for 3779 reflections. The results of the single crystal XRD and thermal analysis confirm that gossypol with 4-picoline forms a trisolvat, and a tetrasolvate with 2-picoline. The transition from 4-picoline to 2-picoline proves to change the type of the host-guest association from one-dimensional to zero-dimensional, i.e., to lead to a new crystal structure. Desolvation of compound 2 begins at a lower temperature than that for compound 1, which is explained by their different crystal structures.