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

Abstract

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.

Keywords

• polyoxomolybdates
• metal tricarbonyl
• electrocatalysts
• Keggin structure