Two New Tetravacant Organometallic Keggin-Type Heteropolyoxomolybdates-Supported Manganese Carbonyl Derivatives.

Two novel heteropolyoxomolybdate [XMo₈O31]n- (X = Ge(1) or P(2)) manganese carbonyl derivatives [(CH₃)₄N]₆H₆{MnII(GeMo₈O31)[MnI(CO)₃]₂}₂·12H₂O (1) and [(CH₃)₄N]₄H₆{MnII(PMo₈O31)[MnI(CO)₃]₂}₂·14H₂O (2), have been successfully synthesized and characterized in the solid state by single crystal X-ray diffraction, IR and thermogravimetric analysis, and in solution by UV-Vis spectroscopy and electrochemistry. The two polyoxomolybdate-based organometallic compounds 1 and 2 represent rare examples of transition metal sandwich-based polyoxometalate metal carbonyl derivatives (PMCDs), in which the organic-inorganic hybrids are composed of four Mn(CO)₃⁺ groups symmetrically occupied the tetravacant sites of dimeric heteropolyoxomolybdate {Mn₂(XMo₈O31)₂}n- through MnI-O-Mo bonds. The carbonyl functionalized Mn atoms are octahedrally coordinated via three μ₂-oxygens of the [XMo₈O31]n- unit and three carbonyl carbon atoms. Interestingly, 1 and 2 form a psedocuboidal ring Mn(CO)₃Mo₃O12 with {Mn(CO)₃}⁺ occupying the three fold axis of the Mo₃O12 octahedral triad. Beside this, the two centrally placed adjacent MnII atoms show intramolecular Mn∙∙∙Mn interactions of 3.11 and 3.16 Å in 1 and 2, respectively. Significant n→π* and O···O intermolecular interactions between the orthogonally aligned adjacent carbonyl groups through the overlap of lone-pair electrons on oxygen atoms with the antibonding orbital (π*) of the adjacent carbony carbon atom of the subsequent units in 1 and 2 were observed. The electrochemical properties of the two compounds were also been investigated.