Cubane, symmetry

Nevertheless, there are situations where one wants to work with six four-membered rings in cubane (e.g., when considering the symmetry of the ring system). In this situation, one adds a sixth four-membered ring to obtain firom the SSSR the so-called extended set of smallest rings (ESSR). 

Although most molecules in point groups /ft, 0, Ta, C, C and C may be assigned by inspection, some appear unusual. Consider the cubic symmetry of cubane. CBH8. To... 

The class of cubane clusters (4w) is large and includes complexes of metals distributed throughout the Periodic Table, with diverse bridging ligands X and with 0-4 terminal ligands L. There is substantial variability of shape, symmetry and dimensions of the central core apart from dissymmetry due to partial substitution of M, X or L, the concentric interpenetrating M4 and X4... 

Structure (7c), two cubanes sharing a metal vertex with M(p3-X)6 octahedral coordination, is confirmed for Me4Zn7(OMe)8 and Et6Zn7(OMe)8.270 Structure (7d), which occurs in (p3-NMe)7-(AlMe)7271 with virtual C3v symmetry, is envisaged as two (MeNAlMe)4 cubanes, one excised of an AlMe vertex and the other excised of an NMe vertex, and connected on the resulting triangular faces by three A1—N bonds. 

The iron-selenium cubane-type cluster [Fe4Se4(NO)4] has been shown (52) to adopt a molecular structure of almost exact Td symmetry, whereas in the corresponding anion [Fe4Se4(N0)4] the symmetry is lowered to D2a, just as for the sulfur analogs (37). Upon one-electron reduction the size of the Fe4 cage increases in the neutral molecule the Fe-Fe and Fe-Se distances are 2.703 and 2.342 A, but in the anion the... 

In tackling problems of molecular and electronic structure such as those posed by these sulfur-bridged tetrametallic clusters, two approaches are possible. One is the construction, often heavily reliant upon symmetry arguments, of a general, essentially qualitative model intended to provide a broad description of a series of molecules the other is a detailed quantum mechanical study, at an appropriate level of theory, of individual molecules, followed by a search for generalization or patterns. A combination of both approaches is usually the most valuable for chemical understanding, and much effort along these lines has been expanded on cubane-type clusters and their derivatives. 

A special case of pyramidal M30 units involves the cubane framework (cf. 26) consisting of a tetrahedron of M atoms linked in threes by the four /x3-O ligands comprising the interpenetrating tetrahedron of oxygens. This framework is generally distorted, often having only Z)2 symmetry. It... 

Iron-sulfur clusters have been investigated extensively by EPR spectroscopy and the observation of a single line for the cubane-like structure [Fe4S4(SR)4]3 (Fig. 3.20) confirms the high symmetry of the molecule and reveals the extent of delocalisation of the electron spin. 

Oh This might be considered cubic symmetry . Example cubane, SF6. 

The geometrical parameters of equilibrium configurations of small fullerenes isolated molecules C , their dimers (Cn)2 and cuban-like clusters(Cn)8 are obtained for n = 20, 24, 28, 32. The Cuban like clusters can be considered as fragments of polymerized crystal structures with simple cubic symmetry. Total energy, heat of formation, energies of HOMO and LUMO orbitals, density of one-electron states (DOS) are determined for equilibrium configurations of all these objects. All the computations are performed by help of pocket PC Gamess in frames of optimized semi-empirical PM3-basis [4-5],... 

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