Theoretical investigation of the pressure-induced insulator-to-metal-to-insulator transitions in one-dimensional bis(dimethylglyoximato) platinum(II), Pt(dmg)₂

The electrical resistivity of one-dimensional bis(dimethylglyoximato) platinum(II), Pt(dmg)₂, exhibits unexpected insulator-to-metal-to-insulator (I-M-I) transitions under the high pressure. The interesting but complicated nature of these pressure-induced I-M-I transitions is approached by the density functional theory calculations on a kind of stacking model. After optimization of one monomer, a set of stacking models with different intermolecular distances (metal-metal bond) are built from 8 units of monomers to simulate the various stages during pressure increasing in experiment. As the metal-metal bond lengths decrease, the calculated HOMO and LUMO energy gaps become narrow and reach the minimum value (0.27 eV) when the metal-metal bond length is 2.4 Å. If the metal-metal bond length is continually decreased for simulating even higher pressure, the energy gaps were found to be enlarged again, at the same time, the natural charge analysis of the models shows the intra-molecular charges transfer from Pt atom to N atoms rather than the inter-molecular one. The entire energy gap change of these stacking model systems is well consistent with the electrical resistivity change in experiment. This similar tendency also indicates that the change of metal-metal bond length and the following unique charge transfer may be the main reason to the pressure-induced I-M-I transitions of Pt(dmg)₂ complexes.