Mixed 1D−2D Inorganic Polymeric Zinc Ferrocenylphosphonate:  Crystal Structure and Electrochemical Study

Needs for ferrocene immobilization on robust host structures are considerable since derivative materials may find applications in medical areas, optical devices, or catalysis. Synthesis of phosphonate functionalized ferrocene allowed its subsequent inorganic polymerization with a zinc salt. The crystallographic structure of the compound obtained, Zn(HO3PFc)2·2H2O, shows a unique two-dimensional ferrocene arrangement anchored on a one-dimensional Zn−O−P−O−Zn backbone. The ferrocene packing in the title compound is very similar to the packing found in molecular ferrocene. The electroactivity of Zn(HO3PFc)2·2H2O is thoroughly studied. It shows a reversible surface oxidation of ferrocene. Mössbauer spectroscopy for the oxidized compound shows an isomer shift of IS 2b = 0.432 mm.s-1 and a quadrupolar splitting of QS 2b = 0.205 mm.s-1, which is consistent with a stable S = 1/2 ferrocenium state. The magnetic susceptibility study, Mössbauer spectroscopy, and galvanostatic titration show that only the ferrocene moieties present at the surface of the crystallites are reversibly oxidized. This observation is reinforced by a complex impedance study showing mainly resistive behavior and conductivity measurements indicating weak, thermally assisted, conductivity. The general properties of this compound demonstrate that phosphonato functionalization may be a useful approach for all fields concerned by immobilization of ferrocene.