Coordination geometry capped square antiprism

Bi-0 2.54(l)-2.68(2) A], In contrast, the nine-coordinate capped square antiprism geometry for bismuth in [Bi(N03)3(H20)3] (18-crown-6) does not involve the expected multidentate ether coordination to bismuth, but rather a hydrogen-bonded interaction of the crown ether with the hydrated bismuth center chelated by bidentate nitrate groups [Bi-0 2.38(2)—2.56(2) A] 32, implying that the hexado-... 

A second form of Nd2(malonate)3 6H2O complex has been reported [169]. In this complex neodymium is nine-coordinate surrounded by six carboxylate, and three water oxygen atoms and the geometry is intermediate between the distorted capped square antiprism and the distorted tricapped trigonal prism. 

Figure 10.3 Coordination geometry of a tricapped trigonal-prism (TTP) and a capped square-antiprism (CSAP) form of Gd-DTPA and Gd-DOTA, respectively [14].

Both these papers describe the nse of qnantum chemical and molecnlar dynamics simulations to stndy the stractnre of the first and second coordination spheres of Th(IV) and to determine the residence time of water in the second coordination sphere. In the second paper the authors discuss the entry of chloride into the second coordination sphere at different concentrations of chloride. The starting point in these studies is the determination of the geometry and relative energy of different hydration isomers of Th(IV) nsing ab initio quantnm mechanics. When the ratio (H20)/(Th" ) is nine, the most stable stractnre, [ Th(H20)g" ] has a geometry (a capped square antiprism). 

As is common with the higher coordination geometries, the interconversion of Dzh Cav niay be easily achieved. The monocapped square antiprism (C4 ) can be generated from the s-tricapped trigonal prism by raising the points a and b (Fig. 27) and lowering the two caps c and d so that the four form the basal plane of the square antiprism. 

Fig. 8.4. Coordination geometries for seven- and eight-coordination (a) pentagonal bipyramid, (b) capped trigonal prism, (c) capped octahedron, (d) cube, (e) square antiprism and (/) triangulated dodecahedron. Central atom-ligand bonds are shown by full lines dashed lines indicate the edges of the polyhedral figure.

---