Acid-Base Equilibrium in the K2SO3-Methanol System

Russian Journal of General Chemistry -     

Crystal Structure Of Betulin Ethanol Solvate

The crystal structure of the 1:1 ethanol betulin solvate, a widely spread natural compound, is determined. The betulin solvate crystallizes in orthorhombic symmetry in the P2₁2₁2₁ space group, Z= 4. The unit cell parameters are as follows: a = 7.0159(1) ?, b = 12.4425(2) ?, c = 33.7500(5) ?; V = 2946.22(8) ?³. Betulin molecules are hydrogen bonded to each other and ethanol molecules, as a result of which the layers are distinguished in the structure, which are perpendicular to the crystallographic direction. Inside the layer, all molecules are hydrogen bonded, while the layers are linked by van der Waals interactions.     

Transitions in Solvate Crystals of a Tetraaryladamantane

Obtaining high-resolution structures of liquid compounds can be difficult. Encapsulating them in the lattice of a larger organic molecule acting as crystallization chaperone is one option to overcome this difficulty. Tetraaryladamantane ethers can play the role of chaperones, accommodating a range of different guest molecules in their crystals. How well-ordered crystalline arrangements for molecules of different shape are achieved is not clear. Cases in which more than one structure is found may shed light on this phenomenon. Here, we report low-order cubic crystal structures of 1,3,5,7-tetrakis(2,4-dimethoxyphenyl)adamantane (TDA) encapsulating ortho-xylene or cyclohexane, together with better ordered structures obtained after warming the crystals to 60 °C. Evidence for cubic crystal systems was also found for limonene, hexachlorobutadiene and eucalyptol, with a transition to a triclinic system for the former two, but no transition up to 70 °C for the latter. These findings indicate that some solvate structures of TDA can readily undergo structural transitions to less solvated, better ordered systems. Crystals obtained by rapid thermal crystallization may be in kinetically trapped states, and the transition to a solvate-free crystal system appears to have a kinetic barrier that depends strongly on the structure of the liquid guest molecules encapsulated in the lattice.