Molecular Nonvolatile Memory Based on [α-GeW12O40]4-/Metalloviologen Hybrids Can Work at High Temperature Monitored by Chromism

The searching for new nonvolatile memories with the ability of working in harsh environments such as high temperature or humidity will be significant for industrial automation. Herein, a thermochromic polyoxometalate-based metal-organic framework (POMOF) constructed from Keggin-type polyoxometalates and metalloviologen has been fabricated as a nonvolatile memory device, which can exhibit stable nonvolatile memory behavior both at room and high temperature (150 degrees C) with stable cycle performance. Furthermore, its extreme working temperature can be monitored by color change from yellow to black, which stems from the reversible thermochromism of the POMOF. Importantly, the crystal structures at room and high temperature (150 degrees C) have been determined, which illustrates that the Keggin-type POM (alpha-GeW12O40)(4-) anions are anchored in the metalloviologen cationic [Co-2(bpdo)(4)(H2O)6](n)(4n+) cavities through numerous C-H center dot center dot center dot O-POM hydrogen bonds. The high temperature could not destroy its framework but remove its three lattice water molecules; in addition, more condensed structures with shorter Ge/W/Co-O lengths, stronger hydrogen bonds, and more distorted terminal bpdo ligands can be observed. Consequently, better cycling stability with a more uniform high-resistance state/ low-resistance state can be achieved. Finally, the charge transport mechanism in this POMOF-based device during the resistive switching process has been discussed. In all, the combination of electron-poor metalloviologen with electron reservoir POM can give rise to the enhanced nonvolatile memory and better thermal stability accompanied with observable chromism.