Redox-active pH-responsive molecules: ferrocenylphosphonic acid, ferrocenylmethylphosphonic acid and 1,1 '-ferrocenylbisphosphonic acid. Structural determination of FcPO(3)Na(2)center dot 5H(2)O

摘要

The acidity constants of the reduced and oxidized species of ferrocenylphosphonic acids FcPO(3)H(2), FcCH(2)PO(3)H(2) and fc(PO2H2)(2) (Fc = (eta(5)-C5H5)Fe(eta(5)-C5H4), fc = (eta(5)-C5H4)Fe(eta(5)-C5H4)) in water have been evaluated by potentiometric, P-31 NMR, and electrochemical methods. The oxidized forms are more acidic than the reduced ones. The interaction between the redox centre and the charged oxygen atoms of the phosphonate group is shown to be electrostatic. The maximum oxidation shift Delta E between the protonated and unprotonated species increases with the number of charges of the substrate and decreases with the increase of the distance between the ferrocenyl centre and the oxygen atoms of the phosphonate group. The structure of FcPO(3)Na(2)center dot 5H(2)O is determined. The compound crystallizes in the monoclinic system. It is lamellar with an inorganic layer formed by tetramers Na4O14, the ferrocenyl groups occupying the interlamellar space.