Hexacapped cube

Burger and Kliifers have reported a tetradecanuclear iron cluster stabilized by a deprotonated poly-ol ligand—me5o-butane-l,2,3,4-tetraol (known as erythritol trivially). The 14 Fe centers form a hexacapped cube which is surrounded by Ca and poly-ol ligands. 

The tetrakishexadron (Oh) can be considered as the combination of a cube and an octahedron. The coordination number is 14. Every face of the original cube is transformed into a tetragonal pyramid, so that the total number of faces is 24. The tetrakishexadron is thus a hexacapped cube (fig. 11). We consider only one radial distance, so that the points of the cube and the octahedron are lying on one sphere. Different tetrakishexadra are possible, the general formula is Ohk (in Miller-indices). The coordinates of the ligands are the same as those of the cube and the octahedron together. Both the fourfold or the threefold rotation axis can be chosen as the quantization axis. 

The number of cluster valence electrons is 66. Based on the examples of metalloid clusters in the text, we don t expect the borane paradigm to work for this closed cluster and it does not (An + 2 = 58 eve). It can be viewed as a hexacapped three-connect (highly distorted) cube giving, via the cluster fusion rule 5 x 8 + 6 x 24 — 6 x 24 [or — 6 x 22] = 40 [or 52] eve. This doesn t work and besides, four of the cube edges have very long Sn-Sn contacts. Finally, it can be viewed with the modified Schleyer approach (no lone pairs on Sn atoms) or the Schleyer approach... 

Another distortion of a body-centered Mg cube is encountered in the related 127-MVE clusters [Cog(//5-Bi)4(CO)i6] (5) recently characterized by Eveland and Whitmire4 If the structure of cluster 5 is viewed as a metal-centered elongated Co8 cube with four Bi atoms capping the four rectangular faces, it bears some structural resemblance to the hexacapped cubic Mg( 4-E)6L8 species such as 3 mentioned aboveEH and DFT calculations were recently performed on compound 5 and related models for comparison with the M9(jt<4-E)6L8 cubic clustersJ ... 

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