1'-Acetylferrocene-1-carboxylic acid: an instance of hydrogen bonding in the rare dimeric acid-to-ketone mode.

The title compound, [Fe(C(6)H(5)O(2))(C(7)H(7)O)], adopts a conformation involving partial staggering of its rings and aggregates in the solid as acid-to-ketone hydrogen-bonding dimers [O.O = 2.720(4)A and O-H...O = 164 degree] having centrosymmetrically related components. Close intermolecular C-H...O contacts were found to both carboxyl O atoms.