Cluster distortions

The preceding three reduced molybdenum clusters indicate that rhomboidal cluster units are common among this kind of oxide, and the Mo-Mo distances in the cluster units are dependent on CVE assignable to the Mo4 units. MO calculations on Mo4 molecular cluster compounds containing 10 CVE and 8 CVE have shown that the 8-electron clusters distort from a second-order Jahn-Teller effect (116). Such a distortion has been observed in the 8-electron W4(OEt)16 (117). 

To estimate the vibronic coupling constant, we performed CF calculations for the UOg cluster distorted along the eg, f2g( 1) and t2g(2) Jahn-Teller modes (Fig. 10). A similar approach was previously applied for calculations of vibronic coupling constants in a series of UXg octahedral complexes (X = F, Cl, Br, and I) and in the U(NCS)g cubic complex in compound (NEt4)4U(NCS)8 [14]. 

When the metal-oxygen bond is sufficiently strong, e.g., as for Ni and Pd, the formation of new interface bonds may compensates the loss of metal-metal bonds and the cluster distorts from its gas-phase geometry (Fig. 2.10i). For weaker metal-oxide bonds, as found for Co, Cu, and Ag, the metal-metal interactions prevail over the metal-MgO ones so that the cluster maintains, to a large extent, its electronic and geometric structure (Fig. 2.10f). Ni4 and Pd4, which form relatively strong bonds with MgO, tend to adhere with more metal atoms to the surface leading to a distorted tetrahedron while in the... 

Full geometry optimizations were also performed for the C58 and C59 clusters. Optimized structures of these complexes are presented in Fig. 9. It is shown that in the case of the C59 cluster, distortions of the ideal structure are much larger than in the case of Csg. 

Hgme 5. Changes in the one-electron energy levels around the HOMO-LUMO gap in Nb I as a function of temperature (or cluster distortion). 

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