3-Fold axis

A ligand such as ethylenediamine is not planar and has a spiral form (gauche) giving rise to further forms. When the direction of one C—C bond in one ethylenediamine is parallel to the 3-fold axis the isomer is termed the le( form, when it is inclined to the axis it is termed the ob form. 

SnMe4 Snl4-like structure. Tetrahedral molecule with 3-fold axis of symmetry along a slightly shorter Sn—C bond. The different Sn—C bond lengths are in accord with NMR, INS and Mossbauer data (see Table 2). 131, 204... 

The remaining three antiparallel /3 structures form a miscellaneous category (see Fig. 84). Lactate dehydrogenase d2 and gene 5 protein each has several two-stranded antiparallel j8 ribbons, but they do not coalesce into any readily described overall pattern. The N-terminal domain of tomato bushy stunt virus protein has a unique /3 structure in which equivalent pieces of chain from three different subunits wrap around a 3-fold axis to form what has been called a /3 annulus (Harrison et ah, 1978). Each of the three chains contributes a short strand segment to each of three three-stranded, interlocking /3 sheets. This domain provides one of the subunit contacts that hold the virus... 

X-ray diffraction analyses revealed isostructural geometries for all trinuclear complexes, where three metal ions are coordinated to two ligand molecules (Fig. 7). Each metal ion is coordinated to two carbenoid carbon atoms each from a different ligand. The structure exhibits a Ds symmetry with the 3-fold axis passing through the anchoring C atoms of the two ligands. 

Folate coenzymes, 803, 804. See also Folic acid Folate receptors 805 3-Fold axis 333 Folding patterns... 

Assume F is a 10-gon. Because of the S-fold rotation mapping of F onto itself, every second vertex of F must meet a 3-fold axis. The three faces containing such a vertex must then all be 10-gons, because they are rotated onto each other. This means that F is completely surrounded by 10-gons, each of them in the same orbit as F. By induction, all the feces in the connected component, which contain F, are 10-gons. There is only one connected component so, there are only 10-gons, a contradiction. 

Figure 7. Chem-X model for a (WC>3)4 cubane-cluster encapsulated in an a-cage of zeolite Y, projected down a 3-fold axis of the host structure, displaying tungsten-dioxo anchoring to extraffamework site II Na+ cation six-ring binding sites.

The more in depth analysis of the SH reconstruction data of Kolb and coworkers [156] on Au(lll) has recently been performed by Lupke et al. [158]. In this work, the second order susceptibility tensor has been split into contributions due to 1-fold, 2-fold, 3-fold and oo-fold axes for a surface of Cs symmetry. Their results suggest that the SH rotational patterns cannot be completely analyzed by theoretical models without knowledge of the distribution of domains present in the reconstruction of the surface. They also conclude that rotation axes of lower symmetry create additional contributions via overtones or harmonics . Their symmetry analysis of the SH rotational patterns from Au(lll) reveals contributions from a 3-fold axis with a regular (lxl) structure and simultaneously from a 1-fold and a 2-fold axis due to the (1x23) reconstruction. 

FIGURE 23. SngSig core of hexastannaprismane 103 projection along the 3-fold axis... 

These molecules have a 3-fold axis going through A and hence have cylindri-cally symmetric field gradients. In a manner similar to that used for the planar molecules the field gradient is given by... 

When BH3 is compared to BF3 an important difference is that the bonding electrons in the latter case contributed by the ligand atoms are of p-type so that 2 x s2 and 2 x p4 electrons are available in the valence shell of the central atom. This distribution is consistent with the familiar 3 x (sp)2 formulation that defines a planar molecule with a 3-fold axis along z. The angular momentum is quenched by pairs of p-electrons rotating in opposite sense around 2. 

There are many other formally low-valent lanthanide compounds that doubtless display extensive metal—metal bonding or contain M cluster units, such as [M5Q] units in the M5QCI9 phases (M = La—Pr), where the M5Q units are trigonal bipyramidal M5 clusters with a Q unit inside on the 3-fold axis.50... 

Fig. 18. The P22 tailspike protein, (a) The main domain (Steinbacher et al, 1994). The protein is trimeric, and the 3-fold axis is parallel to the long axis of the monomer. The G-terminal sheets and the connecting loops link the subunits together, (b) A trimer of the N-terminal head-binding domain seen down the 3-fold axis (Steinbacher et al., 1997).

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