Chiral antiprism

Upon complexation with a lanthanide ion, these complexes may form square antiprism or twisted square antiprism (TS APR) structures with a vacant coordination site in the cap position, which is assumed to be occupied by a solvent molecule. Just as in the chelated complexes described previously, two distinct types of chiral stereochemistry are present. In analogy with OC-6 species, the sense of rotation of the pendant arms is denoted as A or A depending upon if the arms rotate clockwise (A) or counterclockwise (A) as one proceeds down the direction of the C4 axis. There is also chirality (or helicity) associated with the nonplanar 12-membered ring. If one looks along the skew-line connecting the coordinated nitrogens, the carbon atoms... 

Although the number of examples of chiral assemblies formed by the first method have been increasing steeply, and include helicates, trigonal antiprisms, tetrahedral, trigonal bipyramid and cuboctahedra, interest in stereoselective syntheses in coordination chemistry has only been developed in recent years and only a few examples have been reported. 

It has generally been observed that the overall chirality of the electronic transitions from these DOTA-type lanthanide complexes appears to be quite sensitive to the square antiprism... 

The structure of the dimethylformamide adduct of a chiral shift reagent based on 3-trifluoroacetyl-d-camphor has been determined (Cunningham and Sievers, 1975). This compound is a dimeric species, (facam)3Pr(DMF)3Pr(facam)3 in which the three DMF molecules serve as bridging groups. The two praseodymium atoms are nine-coordinate with the oxygen atoms occupying the vertices of a distorted monocapped square antiprism. This structure is particularly... 

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