Control of the electronic phase transition of the MMX-chain complex Pt2(n-pentylCS2)4I with the uniaxial compression

We report the uniaxial compression effect of the electrical resistivity on the quasi-one-dimensional halogen-bridged binuclear metal complex (MMX-chain) Pt2(n-pentylCS2)4I which exhibits successive electronic transitions. At ambient pressure, this complex exhibits first-order phase transition around 210 K between the low-temperature insulating alternate-charge-polarization (ACP; Pt2+-Pt3+-Pt3+-Pt2+) state and the room-temperature conductive averaged-valence (AV; Pt2.5+-Pt2.5+) state, confirmed from the drastic changes of the resistivity and ESR spectra. In the ACP state the thermal activation of the soliton (Pt3+) has been demonstrated from the spin susceptibility enhancement and the motional narrowing of the ESR spectra. Applying the uniaxial piston pressure up to 0.7 GPa, the transition temperature shifts to higher temperatures in both compression directions, parallel and perpendicular to the chain, indicating the stabilization of the ACP state. In the case of the parallel compression, this result is well explained by the increase of the transfer integral (tMX) between platinum and iodine atoms, whereas in the case of the perpendicular one, it should be necessary to consider the modification of the ligand molecules which strongly couples to the phase transition. By comparing with the reported results for Pt2(n-butylCS2)4I with shorter alkyl side chains, the phase stabilization mechanism is discussed.