Uniaxial Negative Thermal Expansion in an Organic Complex Caused by Sliding of Layers

Generally, materials undergo thermal expansion along
all directions
upon heating. The very few materials that show the opposite trend
along one or more of their crystallographic axes have plenty of applications.
Herein we report a negative thermal expansion along one axis in the
crystal structure of a 1:1:1 organic complex of 1,3,5-benzenetricarboxylic
acid (BTA), 2,6-dimethylaniline (DMA), and water molecules. The unusual
thermal expansion in this structure is caused by sliding of layers,
which is unprecedented.