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tert‐Butyl‐1′‐methoxycarbonyl‐1‐ferrocenecarbamate (1) was Boc‐deprotected to give free amine which underwent oxalyl chloride‐mediated dimerization. The structure of the so‐obtained oxalamide‐bridged ferrocene 2 was elucidated using infrared and NMR (1H, 13C, COSY, NOESY, HSQC, HMBC) spectroscopies, crystal structure analysis, and electrospray ionization and high‐resolution mass spectrometry. The preliminary conformational analysis in solution suggested the intramolecular engagement of oxalamide protons, while single‐crystal analysis revealed an intermolecular hydrogen‐bonding pattern. Also, the effect of oxalamide‐bridged ferrocene 2 on cell viability of three human cell lines (HEK293T, HeLa and HepG2) was tested. In vitro screening revealed proliferative as well as cytotoxic effects of the tested compound in the applied concentration range (1–350 μM) on HEK293T and HepG2 cells. Stimulatory effect on cell growth was the most pronounced for normal HEK293T cells, while the highest cytotoxic effect was observed towards HeLa tumour cells and it was dose‐dependent. The observed dual biological activity of 2 implies its potential application in drug development.

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.

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