Negative Linear Compressibility of a Metal–Organic Framework

A 3D hybrid zinc formate framework, [NH₄]­[Zn­(HCOO)₃], possessing an <i>acs</i> topology, shows a high degree of mechanical anisotropy and negative linear compressibility (NLC) along its <i>c</i> axis. High-pressure single-crystal X-ray diffraction studies and density functional theory calculations indicate that contraction of the Zn–O bonds and tilting of the formate ligands with increasing pressure induce changes in structure that result in shrinkage of the <i>a</i> and <i>b</i> axes and the NLC effect along <i>c