Octahedral cluster

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Octahedral clusters are inorganic or organometallic hexameric cluster compounds based on an octahedral geometry. One important class of octahedral clusters are octahedral chalcohalide clusters of the type M₆X₁₂L₆ where M is a metal usually of group 6 or group 7, X is a ligand and more specifically an inner ligand of the chalcohalide group such as chlorine or sulfur and L is an outer ligand. The metal atoms are located on the edges of an octahedron with the interstitial position empty. Each face of the octahedron is capped with a chalcohalide and eight such atoms are at the corners of a cube. For this reason this geometry is called a face capped octahedral cluster. Examples of this type of clusters are the Re₆S₈Cl₆^4- anion and the W₆I₁₄^2- anion, the last one by reaction of tungsten hexacarbonyl with iodine at elevated temperatures.

A special class of compounds are molybdenum clusters of the type A_xMo₆X₈ with X sulfur or selenium and A_x an interstitial atom (for instance PbMo₆S₈) for which a so-called Chevrel phase can be found. These compounds are actively researched for their superconducting properties.

With metals in group 4 or 5 a so-called edge-capped octahedral cluster is found. Four more ligands are included in this cluster each one located at the center of an octahedral edge. Examples of this type of compounds are Nb₆F₁₅ or the Nb₆F₁₈^2- anion.

[edit] References

• Atomlike Building Units of Adjustable Character: Solid-State and Solution Routes to Manipulating Hexanuclear Transition Metal Chalcohalide Clusters Eric J. Welch and Jeffrey R. Long in Progress in Inorganic Chemistry, Volume 54 Kenneth D. Karlin ISBN 0-471-72348-7 2005