The first observation of γ-octamolybdate: synthesis, crystal and molecular structure of [Me 3 N(CH 2 ) 6 NMe 3 ] 2 [Mo 8 O 26 ]·2H 2 O

The compound [Me3N(CH2)6NMe3]2[Mo8O26]·2H2O crystallizes from an aqueous solution of sodium molybdate and [Me3N(CH2)6NMe3]Cl2, slightly acidified with hydrochloric acid. The crystals are monoclinic, space group P21/n with a= 12.42(1), b= 12.897(3), c= 15.74(1)Å, β= 106.41(5)° and Z= 2. The structure was determined by direct methods and refined by least squares to R= 0.030 for 3153 observed reflections and 315 parameters. The [Mo8O26]4– anion is composed of six MoO6 octahedra interlinked along edges and two MoO5 trigonal bipyramids each sharing two edges with the octahedra. This is different from the previously observed α and β isomers of [Mo8O26]4– and lends credence to one of the proposed mechanisms for their interconversion.