Synthesis,structures and properties of two novel charge-transfer complexes with the ratio of ferrocenyl:POM of 1:1, (Bu4N)[CpFeCpCH2N(C2H5)3][M6O19] (M = Mo,W)

The first charge-transfer (CT) complexes containing the cationic ferrocenyl donor CpFeCpCH₂N⁺(C₂H₅)₃ and polyoxometalate (POM) acceptors of the Lindqvist structural type M₆O₁₉]^2? (M=Mo, W) with the ratio of ferrocenyl:POM of 1:1, (Bu₄N)CpFeCpCH₂N(C₂H₅)₃]Mo₆O₁₉] (1) and (Bu₄N)CpFeCpCH₂N(C₂H₅)₃]W₆O₁₉] (2), were synthesized in high yields (67–71%) by traditional solution synthetic method, and characterized by elemental analysis, IR spectroscopy, UV–vis diffuse reflectance spectrum, luminescent spectrum and single crystal X-ray diffraction. The X-ray structure of the two novel CTCs were both solved in the monoclinic space group P2₁/n and show the close interaction of the hydrogen atoms of the CpFeCpCH₂N⁺(C₂H₅)₃ with the oxygen atoms on the surface of the POM. The UV–vis diffuse reflectance spectrum in the solid state indicates the presence of a new CT band at λ_max = 576 nm and 590 nm for 1 and 2, respectively, attributed to CT transitions between the ferrocenyl donors and the POM acceptors. The luminescent spectroscopy of 1 exhibits the weakened fluorescence signals compared to that of the corresponding POM and the cationic donor, however, 2 has an intense emission at about ca. 394 nm and may be excellent candidates for potential solid-state photofunctional materials.