Reversible gas-solid reactions between the organometallic zwitterion [(η5-C5H4COOH)(η5-C5H4COO)CoIII] and vapors of trifluoroacetic and tetrafluoroboric acids

Exposure of the solid zwitterion [(eta(5)-C5H4COOH)(eta(5)-C5H4COO)Co-III] (1) to vapors of CF3COOH and HBF4 quantitatively produces the corresponding salts of the cation [(eta(5)-C5H4COOH)(2)Co-III](+) (2), namely 2[CF3COO] and 2[BF4]. Both heterogeneous reactions are fully reversible; the acids can be quantitatively removed by mild thermal treatment, which regenerates the starting material. Single crystals of 2[CF3COO] and 2[BF4] for X-ray diffraction can be obtained if the same reaction is carried out in solution. They possess the same structures as those produced in the gas-solid reactions.