From calcium interaction to calcium electrochemical detection by [(C5H5)Fe(C5H4COCH=CHC6H4NEt2)] and its two novel structurally characterized derivatives

[(C5H5)Fe(C5H4COCH=CHC6H4NEt2)] (1) has been electrochemically evaluated toward different cations in solution. Calcium sensing by this compound and its two new derivatives [(C5H5)Fe(C5H4CO(CH=CH)(2)C6H4NMe2)] (2) and [(C5H5)Fe(C5H4CH=CHCOCH=CHC6H4NEt2)] (3) that exhibit a conjugated link between the ferrocene unit and the nitrogen atom has been thoroughly examined. Compounds 2 and 3 have been structurally characterized by single-crystal X-ray diffraction studies. The three related protonated species [1H][BF4] (4), [2H][BF4] (5), and [3H][BF4] (6) have been isolated in a good yield. NMR experiments clearly established that calcium interaction occurs in the vicinity of the carbonyl group, and mass spectrometry studies confirmed that this interaction, which involves several ligand-Ca2+ adducts, is complex. A combination of electrochemical and NMR experiments highlighted an original salt influence on the electrochemical calcium sensing result.