Synthesis and Structures of the Capped and Sandwiched Cobalt Heptamolybdate Polyoxometalate (NH₄)₆{[Co(H₂O)₅][Mo₇O₂₄][Co(H₂O)₂][Mo₇O₂₄][Co(H₂O)₅]} · 6 H₂O and Its Extended Structure (NH₄)₆{[Co(H₂O)₂]₃[Mo₇O₂₄]₂}

Abstract

Two polyoxometalate-based compounds containing the heptamolybdate anion and cobalt(II) have been synthesized, structurally characterized via single-crystal X-ray diffraction and spectroscopically analyzed with solid-state UV–Vis–NIR. The first crystal structure presented is a capped- and sandwich-style polyoxometalate (NH4)6{[Co(H2O)5][Mo7O24] [Co(H2O)2][Mo7O24][Co(H2O)5]} · 6 H2O (Co3Mo14-POM). This orange product crystallizes in the P-1 space group and has an interesting structure for polyoxometalates (POMs). Here, the cobalt(II) groups are functioning both as a bridge between two heptamolybdate units and also capping units at the top and the bottom of the polyoxometalate. The second structure, another product within the same reaction, is constructed on a similar bonding motif but now forms an extended structure: (NH4)6{[Co(H2O)2]3[Mo7O24]2} (Co3Mo14-ES). This compound also crystallizes in the space group P-1 but is easily separated due to its much darker red-violet color. These structures present themselves as a noteworthy compounds within POM-based crystal structures. Herein, the syntheses, crystal structures and characterization of these compounds are presented.

Keywords

• polyoxometalates
• heptamolybdate
• cobalt
• crystal structures