Organometallic–inorganic charge transfer salts containing a cationic iron mixed sandwich and polyoxomolybdate anions: Syntheses, X-ray molecular structures and spectroscopic properties

Two new organometallic–inorganic charge transfer salts formulated as [(η5-Cp)Fe(η6-MeO-p-C6H4–NHNH2)]2[Mo6O19], 1, and [(η5-Cp)Fe(η6-MeO-p-C6H4–NHNH2)]4[β-Mo8O26], 2, were prepared through a metathesis reaction between the organometallic hydrazine precursor [(η5-Cp)Fe(η6-MeO-p-C6H4–NHNH2)]+PF6− and either [n-Bu4N]2[Mo6O19] or [n-Bu4N]4[α-Mo8O26] in acetonitrile. In the second case, the [α-Mo8O26]4− anion transforms into the [β-Mo8O26]4− isomer. These organometallic–inorganic hybrids were characterized by spectroscopic techniques (IR, 1H NMR and UV–vis). In addition, the UV–vis diffuse reflectance spectra of 1 and 2 in solid state exhibit a band at λmax = 475 and 470 nm, respectively, not observed in DMSO solution, which have been attributed to a charge transfer transition. On the other hand, the solid state structure of 2, solved by X-ray diffraction analysis shows the formation of hydrogen bonds between the protons of the –NHNH2 and C–H groups with the terminal oxo groups of the β-octamolybdate anions [β-Mo8O26]4−. Finally, hybrid 3, formulated as [(η5-Cp)Fe(η6-C6H5OMe)]4[β-Mo8O26] was prepared in EtOH under solvothermal conditions. The single crystal X-ray structure shows the elimination of the –NHNH2 group from the organometallic mixed sandwich reducing its associative ability toward the oxo groups of the counterion only to the electrostatic interactions and to the very weak CH⋯O hydrogen bonds.