Temperature- and Pressure-Induced Structural Changes of Cobalt(II) in a Phosphonium-Based Ionic Liquid

The temperature- and pressure-induced paramagnetic switching of cobalt(II) complex in a binary mixture of phosphonium-based ionic liquid [P-6,P-6,P-6,P-14]SCN and [Co(NCS)(2)] is reported. This arises from a structural change in the coordination of the cobalt(II) center from tetrahedral [Co(NCS)(4)](2-) to octahedral [Co(NCS)(6)](4-) when mobile thiocyanate ions are added. These properties are reflected in the abrupt change of the conductivity behavior of the magnetic ionic liquid. Therefore, as demonstrated herein, the reversible switching in coordination of cobalt from tetrahedral to octahedral can be easily monitored at ambient as well as elevated pressure by tracking the dc-conductivity changes.