Distortion twist

In fact the vast majority of 6-coordinate complexes are indeed octahedral or distorted octahedral. In addition to the twist distortion just considered distortions can be of two other types trigonal and tetragonal distortions which mean compression or elongation along a threefold and a fourfold axis of the octahedron respectively (Fig. 19.8). 

Figure 13. Calculated v(M—S) frequencies for trigonal-prismatic MS6 unit as a function of trigonal-twist distortion. Calculation based on a Urey-Bradley force field for M = Nb with the bidentate bite b = 1.31, K° = 1.57 mdyn A-1 and F = 0.22 mdyn A-1. [Reprinted with permission from K. Tatsumi, I. Matsubara, Y. Sekiguchi, A. Nakamura, and C. Mealli, Inorg. Chem., 28, 773 (1989). Copyright 1989 American Chemical Society.]...

Figure 4. Distortion of the leucite structure as induced by temperature or composition, viewed along [110], Smaller channel cations effect a twisting distortion about the c axis, resulting in axial elongation along c and radial compression along a. From Figure 9 in Palmer et al. (1997).

A more detailed analysis has to take into account the number of carbon atoms in the substituents and their branching. The a-donating and hyper-conjugative interaction of the alkyl substituents appears to play an important role in the dependency of the IP values on substitution pattern. With a few exceptions, the out-of-plane particularly twist distortions of tetrasubstituted ethylenes appear to be too small for a shift in ionization potential (213)... 

London penetration depth, At, is the penetration length of the twist distortion, and the equivalent of the coherence length, co, is the correlation length of the smectic phase. In a screw dislocation, the core of the defect approximates to the smectic correlation length and a twist of 90° to the penetration depth, see Fig. 14(b). 

Electric field effects are more complicated because of conduction. The Carr-Helfrich instability, which occurs in nematics of negative dielectric anisotropy (see 3.10.2), may be expected to take place in this case too, only the bend and twist distortions are now coupled. Moreover, the fluid motion along z can occur only by the process of permeation ( 4.5.1). 

Finally, in addition to predictions for the increments in Miesowicz and Leslie viscosities, the Brochard theory predicts [Brochard, 1979] the increment Syi in the viscosity associated with the twist distortion of a nematic solvent on dissolution of a polymeric solute ... 

Chen, F. L., and Jamieson, A. M., Molecular weight-dependent behavior of the twist distortion in a nematic monodomain containing a main-chain hquid crystal polymer. Macromolecules, 27, 1943-1948 (1994). 

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