Synthesis of 1-(1-ferrocenylethyl)-pyridinium chloride and its hybrid materials with lindquist-type polyoxometalates

A new ferrocene derivative, 1-(1-ferrocenylethyl)-pyridinium (fep = CpFeCp–CH(CH3)–Py+) chloride, and two charge-transfer salts (CTSs) based on the cationic fep donor and Lindqvist-type polyoxometalate acceptors, [fep]2[Mo6O19] (1) and [fep]2[W6O19] (2), were synthesized. fepCl was characterized by elemental analysis, IR spectroscopy and 1H NMR and the two CTSs were characterized by elemental analysis, IR spectroscopy, UV–vis diffuse reflectance spectrum, cyclic voltammetry, fluorescence spectrum and single crystal X-ray diffraction. X-ray crystallographic studies of the brownish red CTSs 1 and 2 reveal that they are isostructural and crystallize in the monoclinic space group P21/n. In salts 1–2, fep and polyoxoanions are cocrystallized by Coulombic forces, and there also exist the complex C–H⋯π and π⋯π stacking interactions between the adjacent fep cations and C–H⋯O hydrogen bonds between the adjacent fep cations and polyanions. The UV–vis diffuse reflectance spectra indicate the presence of a broad charge-transfer band between 500 and 850 nm for 1–2, and CT character of 1 and 2 is also confirmed by the Mulliken correlation between the CT transition energies and the reduction potentials of the polyoxometalate acceptors.