# Large elastic recovery of zinc dicyanoaurate

## TL;DR

This study investigates zinc dicyanoaurate's mechanical properties, revealing its exceptional elastic recovery due to supramolecular helices, which could inspire the design of resilient functional materials.

## Contribution

It demonstrates the strong elastic recovery of zinc dicyanoaurate and links this property to its supramolecular helical structure, providing insights for designing deformation-resistant materials.

## Key findings

- Exhibits strong elastic recovery due to supramolecular helices.
- Elastic response is intermediate between dense and open frameworks.
- Helical motifs can enhance resistance to plastic deformation.

## Abstract

We report the mechanical properties of the `giant' negative compressibility material zinc(II) dicyanoaurate, as determined using a combination of single-crystal nanoindentation measurements and \emph{ab initio} density functional theory calculations. While the elastic response of zinc dicyanoaurate is found to be intermediate to the behaviour of dense and open framework structures, we discover the material to exhibit a particularly strong elastic recovery, which is advantageous for a range of practical applications. We attribute this response to the existence of supramolecular helices that function as atomic-scale springs, storing mechanical energy during compressive stress and hence inhibiting plastic deformation. Our results are consistent with the relationship noted in [Cheng \& Cheng, \textit{Appl. Phys. Lett.}, 1998, {\textbf{73}}, 614] between the magnitude of elastic recovery, on the one hand, and the ratio of material hardness to Young's modulus, on the other hand. Drawing on comparisons with other metal--organic frameworks containing helical structure motifs, we suggest helices as an attractive supramolecular motif for imparting resistance to plastic deformation in the design of functional materials.