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11. 10. 2002.
Supramolecular gas–solid reaction between formic acid vapours and solid [CoIII(η5-C5H4COOH)(η5-C5H4COO)]
Exposure of the solid zwitterion [CoIII(η5-C5H4COOH)(η5-C5H4COO)] to vapours of formic acid quantitatively produces the co-crystal [CoIII(η5-C5H4COOH)(η5-C5H4COO)] [HCOOH] without proton transfer from formic acid to the deprotonated –COO− group on the zwitterion; formic acid can be quantitatively removed by mild thermal treatment, regenerating the starting material.