Dihedral angles distortion

Figure 15.6 Various representations of the molecular structure of ryclc-Si2 showing S atoms in three parallel planes. I he idealized point group symmetry is and the mean dihedral angle is 86.1 5.5 . In the crystal the symmetry is slightly distorted to C21, and the central group of 6 S atoms deviate from eoplanarily by 14pm.

If the BF2 groups in Ni(dmg-BF2)2 are substituted by BPh2 units (122), the complex also adopts the saddle-shaped conformation of type D (Fig. 32), in which the two dimethylglyoxime fragments are bent down from the N4 plane with a dihedral angle of about 27° between the two least-squares planes of the dioxime units. The coordination geometry around the nickel ion is distorted square-pyramidal, but there are no intermolecular Ni Ni interactions [167]. 

It is difficult to decide whether the discrepancy between the calculated and experimental data is due to a different conformational preference of the thietane dioxides in the liquid and the solid phase, or to the crude approximations included in the Karplus-Barfield equation. However, the relationship between vicinal coupling constants and dihedral angles appears qualitatively valid in thietane oxides and dioxides, particularly if trends instead of exact values are discussed . At any rate thietane dioxides, 1,3-dithietane dioxides and tetroxides maintain either planarity or a slightly distorted average vibrating conformation with a low barrier to ring planarity . 

The only known complex with a (RSb)5 ligand is cyclo-[ i-(Me3SiCH2Sb)5-Sb1,Sb3- W(CO)5 2].125 The molecular structure is depicted in Fig. 25. The antimony ring adopts a slightly distorted envelope conformation with a Sb4/Sb3 dihedral angle of 129.1°. The metalcarbonyl units are in 1-3 positions trans to each other. 

The structure of the Z-isomer was determined (Figure 21) indicating considerable pyramidal distortion at the germanium, reflected in the large dihedral angle (36°) at these atoms. Kinetic investigations H-NMR) of the Z-E isomerization in CgDg indicated that the equilibrium is shifted to the Z-isomer [(E)/(Z) values are 0.490 at 40.1 °C and 0.368 at 17.0 °C],... 

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