Room-temperature bistability in a cobalt-octacyanidotungstate framework showing a charge-transfer phase transition with a red-blue color change

A two-dimensional cyanido-bridged Co-W assembly, Cs-0.1(+)(H5O2+)(0.9) [Co(4-bromopyridine)(2.3){W(CN)(8)}], was synthesized. This compound has a layer structure with H5O2+ and Cs+ ions in between the cyanido-bridged Co-W coordination sheets, and exhibits a charge transfer-induced phase transition between Co-II-W-V (red) and Co-III-W-IV (blue) states with a drastic color change. Upon cooling, the phase transition from the Co-II-W-V state to the Co-III-W-IV state occurs at 276 K, while the opposite transition from the Co-III-W-IV state to the Co-II-W-V state occurs upon heating at 329 K. The present compound shows a large thermal hysteresis loop with a width of 53 K and bistability at room temperature. Analysis of the thermal phase transition using the Slichter-Drickamer model reveals the thermodynamic parameters of the transition enthalpy, transition entropy, and interaction parameter.

Automated summary

A two-dimensional cyanido-bridged Co-W assembly with layer structure was synthesized, showing a charge transfer-induced phase transition and drastic color change. The compound exhibits a wide thermal hysteresis loop and bistability at room temperature.