The fundamental mechanical properties of a dense metal–organic framework material, [NH₂CHNH₂][Er(HCOO)₄] (1), have been studied using nanoindentation technique. The results demonstrate that the elastic moduli, hardnesses, and yield stresses on the (021)/(02−1) facets are 29.8/30.2, 1.80/1.83 and 0.93/1.01 GPa, respectively. Moreover, variable-temperature powder and single-crystal X-ray diffraction experiments reveal that framework 1 shows significant negative thermal expansion along its b axis, which can be explained by using a hinge–strut structural motif.

Journal of Solid State Chemistry, 2015

Fig. 1. Crystal structure of framework 1 viewed along the (021) (a) and (02?1) direction (b).