Novel charge-ordering and photo-induced phase transition in MMX chain compounds : R4[Pt2(pop)4I]

We report the phase control and photo-induced transition of the one-dimensional iodine-bridged binuclear Pt compounds. Chemical modification of the counter ions located between chains enable us to control the charge and spin configurations on the chains between the diamagnetic charge density wave (CDW) state and the paramagnetic charge polarization (CP) state. In [(C 2 H 5 ) 2 NH 2 ] 4 [Pt 2 (pop) 4 I] (pop=P 2 O 5 H 2 2-), a pressure-induced transition accompanied by a large hysteresis loop (ca. 0.4Gpa) was identified. The transition between the CDW and CP states can be driven within this hysteresis loop by photo-irradiation.