Monosubstituted ferrocenyl chalcones: Effect of structural changes upon the ability to detect calcium by absorption spectroscopy

We show how structural changes in the basic framework of ferrocenyl chalcone [(C5H5)Fe(C5 H4COCHdouble bond; length as m-dashCHC6H4NEt2)] (1) induce different capabilities of detecting calcium by UV/vis absorption spectroscopy. In particular, compound 1, and its derivatives (2) and (3) incorporating a supplementary ethylenic unit into the conjugated link, allow a specific detection of calcium triflate with regard to calcium perchlorate. Investigations related to the unprecedented behaviour of these chalcone-like derivatives are presented. This study confirms that while the interaction of ligands 1–3 with calcium is centred on the CO group, the interaction of ligand 4 with calcium is aza-centered. The strength of these interactions was examined by processing the UV/vis absorption data with a curve fitting model. Remarkably, in the case of compound 4, the set of association constants issued from processing the absorption data was successfully used to fit the NMR data. In addition, mass spectrometry experiments provided strong support for the formation of the different species involved in the interaction of compounds 1–4 with calcium. This work underlines the importance of considering the nature of the salt used as well as the experimental conditions in cation detection processes.