Uniaxial negative thermal expansion induced by moiety twisting in an organic crystal

Abstract

Variable temperature single-crystal X-ray diffraction reveals uniaxial negative thermal expansion (NTE) of 1,4-bis(1′-hydroxycyclopentyl)-1,3-butadiyne crystal. The length of the unit cell axis a decreases with increasing temperature, whereas the b and c axes increase. The mechanism of the negative thermal expansion in the organic crystal has been derived by analysis of the crystal structures at different temperatures. Steric adjustment of the molecules in the crystal structure requires twisting of the terminal cyclopentyl ring, which drives the contraction of one of the principal axes.