Two contrasting observations for halogen (X)-bridged binuclear platinum complexes R-4[Pt-2(P2O5H2)(4)X].nH(2)O are interpreted by finite-temperature Hartree-Fock calculations. Assuming pressure-induced simultaneous increases of the interdimer electron transfer and Coulomb repulsion, we reveal that an applied pressure turns the initial charge-polarization state into a charge-density-wave state at high temperatures. while the,late. oppositely declines with increasing pressure. it low temperature. We predict pressure-induced phase transitions in another family of MMX complexes. Pt-2(CH3CS2)(4)I, as well.