Heteroannularly substituted ferrocene derivatives can act as model systems for various hydrogen-bonded assemblies of biomolecules formed, for instance, by means of O-H...O and N-H...O hydrogen bonding. The crystal structure analysis of 1'-(tert-butoxycarbonylamino)ferrocene-1-carboxylic acid, [Fe(C(10)H(14)NO(2))(C(6)H(5)O(2))] or (C(5)H(4)COOH)Fe(C(5)H(4)NHCOOC(CH(3))(3), reveals two independent molecules within the asymmetric unit, and these are joined into discrete dimers by two types of intermolecular hydrogen bonds, viz. O-H...O and N-H...O. The -COOH and -NHCOOR groups are archetypes for dimer formation via two eight-membered rings. The O-H...O hydrogen bonds [2.656 (3) and 2.663 (3) A] form a cyclic carboxylic acid dimer motif. Another eight-membered ring is formed by N-H...O hydrogen bonds [2.827 (3) and 2.854 (3) A] between the N-H group and an O atom of another carbamoyl moiety. The dimers are assembled in a herring-bone fashion in the bc plane.