Structural Origins of the Anisotropic Thermal Expansion of BINOL Crystals

Measurement of the unit cell of (R)-BINOL over a 200° temperature range (300–100 K) reveals an anisotropic contraction where the c-axis contracts ca. 2.3% compared to a ca. 0.45% contraction of the a and b axes, a ca. six-fold difference in linear thermal expansion coefficient. This contraction corresponds to a decrease in the helical pitch of the 3₁ screw axis in the [001] direction. The anisotropic nature of the contraction is rationalised by a thorough analysis of intermolecular contacts within the crystal and their impact on the conformation of the molecule and crystal packing.

The crystal structure of (R)-BINOL exhibits a pronounced anisotropic thermal expansion.