Synthesis, Structure, and Behavior in Solution of the Dawson Thio Derivative [(P 2 W 17 O 61 ) 2 (H 4 Mo 4 S 4 O 6 )] 16–

The [(P 4 W 34 O 61 ) 2 {Mo 4 S 4 O 4 (OH 2 ) 2 }] 16– anion was obtained by the stereospecific addition of the [Mo 2 S 2 O 2 ] 2+ oxothio cation to the monovacant α 2 ‐[P 2 W 17 O 61 ] 10– anion. The mixed salt K 9 Na 7 [(P 2 W 17 O 61 ) 2 {Mo 4 S 4 O 4 (OH 2 ) 2 }] · 50H 2 O was isolated as single crystals and characterized by X‐ray diffraction. The analysis reveals that the anion adopts a “sandwich‐like” dimeric structure in which the two α 2 ‐[P 2 W 17 O 61 ] 10– subunits are assembled in a transoid disposition with respect to the central cluster {H 4 Mo 4 S 4 O 6 }. In aqueous solution, an isomerization process is evidenced by 31 P NMR spectroscopy and interpreted as the formation of the related cisoid isomer. A ratio of 30:70 of the transoid and cisoid isomers was found at equilibrium. The kinetic constants and activation parameters of the isomerization process were determined by variable‐temperature 31 P NMR experiments. At 303 K, the process was slow ( t 1/2 = 160 min). The activation parameters are discussed with regard to a possible isomerization mechanism.