Welcome to the Sunday ChemistryViews Quiz!

We explore a chemistry topic in this fun and short quiz which will be out in irregular intervals on a Sunday morning. Test your knowledge and learn something new in just a few minutes.

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The Keggin ion is a type of polyoxometalate with a tetrahedral central atom surrounded by twelve metal-oxygen octahedra—true or false? 🤔

See answer

✅ True

🔬 Structure

The α-Keggin ion is a polyoxometalate (POM) with the general formula [XM₁₂O₄₀]ⁿ⁻, where: X = P⁵⁺, Si⁴⁺, B³⁺, As⁵⁺, Co²⁺, Co³⁺, Cu⁺, Cu²⁺, Fe³⁺, etc. and M = Mo⁶⁺, W⁶⁺, V⁵⁺, Ti⁴⁺

The tetrahedron is enclosed by 12 octahedral MO₆ units, which are connected through neighboring oxygen atoms. There are a total of 24 bridging oxygen atoms linking the 12 addenda atoms. The metal centers in the 12 octahedra are arranged in four M₃O₁₃ units on a sphere, nearly equidistant from each other, giving the entire structure a tetrahedral overall symmetry.

The structure self-assembles in acidic aqueous solutions and is the most stable form of polyoxometalate catalysts.

🔎 Discovery
In 1826, Jöns Jakob Berzelius (1779–1848) first reported the α-Keggin anion, ammonium phosphomolybdate ([NH₄]₃[PMo₁₂O₄₀]).

💥 Characterization
In 1933, James Fargher Keggin (1905–1993) experimentally determined the structure of α-Keggin anions using X-ray diffraction [1]. It remains one of the most studied POM structures in chemistry.

[1] James Fargher Keggin, Structure of the Molecule of 12-Phosphotungstic Acid, Nature 1933, 131, 908–909. https://doi.org/10.1038/131908b0

⚙️ Applications
o α-Keggin anions act as catalysts in hydration, polymerization, and oxidation reactions.
o POMs are valuable in multiple disciplines, including physics, materials science, catalysis, biology, and medicine.

👉 Fun Facts

o In 1929, Linus Pauling (1901–1994) proposed a structure for the Keggin ion and thereafter tried to attract the interest of the Bragg group at the University of Manchester, UK, then the leading center for crystal structure elucidation.
o James Fargher Keggin was a young researcher in the lab of Nobel laureate Lawrence Bragg (1890–1971) at Manchester.
o His short paper in Nature, which reported the structure that now bears his name, made his legacy unforgettable.