Catalytic consequences of composition in polyoxometalate clusters with keggin structure

(Graph Presented) Rate constants for acid-catalyzed butanol dehydration on Keggin-type polyoxometalate clusters H_8-nXⁿ⁺W ₁₂O₄₀ (X=P, Si, Al, Co) increase as the oxidation state of the central atom increases and the number of cluster protons concurrently decreases (see diagram). These trends reflect the lower deprotonation enthalpies of clusters with high valent central atoms and their stability as the anionic conjugate base in ionic transition states involved in dehydration catalysis.