Probing the structural and electronic response of Magnus green salt compounds [Pt(NH2R)4][PtCl4] (R = H, CH3) to pressure

Abstract

Despite possessing the desirable crystal packing and short Pt⋯Pt stacking distances required for a large piezoresistive response, the conductivity-pressure response of the Magnus green salt [Pt(NH₃)₄][PtCl₄] is extremely sluggish. Through a combination of high-pressure X-ray diffraction and hybrid-DFT solid state calculations this study demonstrates that the poor conductivity-pressure response is due to a low volumetric compression anisotropy, a relatively large ambient pressure band gap and a lack of dispersion in the conduction band. Ligand modification (from NH₃ to NH₂CH₃) does not enhance the piezoresistive response, causing even lower anisotropy of the volumetric compression and an unexpected phase transition at above 2 GPa. This study demonstrates that consideration of frontier band dispersion is a key design criterion, alongside crystal packing and Pt⋯Pt stacking distances, for piezoresistive materials.