Pressure Driven Ligand Rearrangement Reaction in a Cobalt−Chloride Complex

We report experimental results concerning the occurrence and rate of the reaction CoCl2(EtOH)2 + 4EtOH --> Co(EtOH)(6)(2+) + 2Cl(-) induced by transient high pressure. The experimental probe used to interrogate the system was time-resolved visible light spectroscopy; The transient high pressures induced in the samples were produced by projectiles launched by a single-stage gas gun; consequently, the hydrodynamic flows experienced by the samples were well-defined. The pressures the test samples were subjected to were in the range 0.75-6.7 GPa. Ambient-pressure control experiments, in which the reaction was induced by altering sample temperature, are also reported. For a 20/80 wt % CoCl2 . 6H(2)O/EtOH solution, shocked to ca. 6.7 GPa, we observed the disappearance of signature spectrum of the CoCl2(EtOH)2 species and the appearance of the spectrum of the Co(EtOH)(6)(2+) structure. The cobalt structure on the left side of the equilibrium equation above is tetrahedral, while that on the right is octahedral. In shock-pressurized systems, we have observed the disappearance of the tetrahedral complex and found the time scale for this process is ca. 200 ns. Similarly, in other shock experiments, we have observed the appearance of the octahedral complex and found the time scale for this process is ca. 500 ns. The relevance of the present results to ideas concerning the character of ionic chemical reactions possibly important in detonating condensed-phase explosives is briefly discussed.