Synthesis And Properties Of Charge-Transfer Salts Based On Ferrocene-type Donors And Polyoxometalate Acceptors

Polyoxometalates (POMs) are a unique large class of metal-oxygen clusters, have attracted great attention in recent years due to their versatility and utility in many fields of research such as catalysis, electrical conductor, nonlinear optical materials and liquid crystal. POMs have been widely used as electron-acceptors in charge-transfer materials and cocrystallized with electron-rich organic donors. This paper mainly focuses on charge-transfer salts (CTS) based on ferrocene and its derivatives with POMs. We synthesized six novel charge-transfer polyoxometalates (CTPs).CTP based on ferrocene donor: [Fe(Cp)₂]₄H[GeMo₁₂O₄₀]·CH₃CN·H₂O( 1)CTPs based on ferrocenylmethyltrimethylammonio donor: [CpFeCpCH₂N(CH₃)₃]₄[PMo₁₂O₄₀]·CH₃CN(2) [CpFeCpCH₂N(CH₃)₃]₄[GeMo₁₂O₄₀](3) [CpFeCpCH₂N(CH₃)₃]₄[SiMo₁₂O₄₀](4)CTPs based on ferrocenylmethylpyridinium donor: [CpFeCpCH₂Py]₂Mo₆O₁₉(5) [CpFeCpCH₂Py]₂Mo₆O₁₉(6)The new compounds were characterized by IR, UV-vis and diffuse reflectance spectrum, Elemental analysis, and X-ray single-crystal analysis, as well as CV, fluorescence and EPR properties.Single-crystal X-ray of the title compounds (1) - (6) illustrated that there exist the complex interactions between the polyanions, and the cyclopentadienyl rings/cationic anchors of ferrocene-type electron donor and the framework oxygens of polyanions in the solid state. The UV-vis spectra in concentrated solution or the solid state of the title compounds showed a new charge-transfer absorption band, and the interaction between the ferrocene-type donors and the polyoxometalate anions must play a role in the observed CT effect if the distance of both is short enough. When the ferrocenyl donors were appended to the different POM acceptors by Coulombic forces in ion pairs consisting of (partially or fully) oxidized donors and reduced POMs to yield charge-transfer salts, the fluorescences were obviously distinct (stengthened or weakened, and even quenched). The EPR spectra of powdered samples at 77 K show a single of Mo^V, which means the charge-transfer transition took place between the ferrocenyl donors and the POM acceptors.