Giant anisotropic thermal expansion of copper-cyanido flat layers with flexible copper nodes.

Flat layers are usually considered as structurally rigid motifs in two-dimensional (2D) materials. In this work, we demonstrate that a flat honeycomb-layer composed of distorted tri-coordinate copper ions bridged with cyanidos in (tetraethylammonium)Cu 2 (CN) 3 exhibits high in-plane flexibility. This resulted in an extremely large anisotropic 2D-thermal expansion.