Hexacap

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... 

Hexacapped Cubic Transition Metal Clusters and Derivatives - a Theoretical Approach... 

All calculations reported for 120-electron M8(//4-E)6L8 complexes are in agreement with these qualitative considerations. A HOMO-LUMO gap larger than 1 eV is computed for the 120-MVE Ni8(//4-PH)6(CO)s cluster. " The occupation of the strongly antibonding LUMO would probably result in the breaking of the hexacapped cubic framework. Accordingly, no Mg( 4-E)6Lg species with more than 120 MVEs has been reported. 

The hexacapped cubic framework of electron-deficient M8(/ 4-E)6Lg clusters are only moderately distorted away from the ideal Oh symmetry. Compared with that of the 120-MVE compounds, the slight reduction of the average Ni-Ni separations observed in the electron-deficient nickel species (Table 1) is consistent with the weak M-M antibonding character of some of the MOs which are depopulated. Most of these clusters have a small HOMO-LUMO gap and/or a high-spin configuration. Xa calculations performed by Karplus and coworkers have shown that the singlet and triplet states in electron-deficient species with a Cog( 4-S)6 core and an even number of electrons are nearly isoenergetic, and that the distortion away from... 

Several hexacapped eubic clusters containing a transition metal atom lodged at the center of the cubic core have been structurally characterized. These compounds of formula M9( 4-E)6Ls, listed in Table 1, are known for M = Ni or Pd. A typical example of this new class of electron-rich compound is the 124-MVE compound Ni9(/ 4-GeEt)6(CO)8 (3) characterized by Dahl and coworkers.With MVE counts varying from 121 to 130, they are more electron-rich that their non-centered Mg(/ 4-E)6L8 parents, which contain a maximum of 120 MVEs vide supra). 

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 ... 

Hexacapped cubic species with an interstitial main group element instead of a transition metal are rather scarce. Hitherto, only one example, namely the 119-MVE compound Nig(//g-As)(/i4-As)6(PPh3)8 (6) has been prepared. The structural arrangement of this cluster reported by Fenske and coworkers is strongly related to that of the metal-centered Ni9(//4-As)6(P-Bu"3)g with comparable Nis Nis and Nij-As separations. 

The empty hexacapped Mg(/i4-E)6Lv architecture is permitted for a broad range of electron counts. The upper limit (120 MVEs) corresponds to a closed-shell elec-... 

SEED PIECE PROTECTANT CAPTEX FLIT 406 HEXACAP KAFTAN MERPAN ORTHOCIDE OSOCIDE VANICIDE... 

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. 

Gautier R, Halet J-F, Saillard J-Y (1999) Hexacapped cubic transition metal clusters and derivatives a theoretical approach. In Braunstein P, Oro L, Raithby PR (eds) Metal clusters in chemistry, vol 3. Wiley, Weinheim, pp 1643-1663... 

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