Ferrocenecarboxylic acid is the organoiron compound with the formula . It is the simplest carboxylic acid derivative of ferrocene. It can be prepared in two steps from ferrocene by acylation with a 2-chlorobenzoyl chloride followed by hydrolysis.
On a two-dimensional surface, most carboxylic acids form hydrogen-bonded dimers. Ferrocenecarboxylic acid instead forms a mixture of dimers and cyclic pentamers and organizes into a quasicrystalline order with fivefold symmetry, the first known molecular quasicrystal.
The pK<sub>a</sub> of ferrocenecarboxylic acid is . The acidity increases more than a thousand-fold, to upon oxidation to the ferrocenium cation.
By treatment with thionyl chloride, the carboxylic acid anhydride () is produced.
Derivatives of ferrocenecarboxylic acid are components of some redox switches.