Mechanical and electronic properties of π-conjugated metal bis(dithiolene) complex sheets

Using first-principles calculations, we have investigated the mechanical properties and electronic structures of π^-conjugated metal bis(dithiolene) complex sheets (MC₄S₄), where M = Ni and Pd. First, the sheets are much softer than graphene due to their large porosity. At zero strain, NiC₄S₄ is a semiconductor with an indirect gap, while PdC₄S₄ is a metal. Under either biaxial or uniaxial strain, our band structure analysis demonstrates that the band gap of the NiC₄S₄ slowly decreases to zero with increased strain, which can be attributed to the gradual weakening of π-bonds of the sheet. However, the PdC₄S₄ becomes a magnetic system beyond the deformation threshold that causes a plastic deformation along the X-axis. In addition, we also observe that both two-dimensional sheets undergo different types of nonreversible plastic changes under the uniaxial strains along the X- and Y-axes.