Trigonal antiprismatic geometry

Two similar systems of trigonal antiprismatic geometry are represented by dimeric calixarene capsules that are also based on only five building units [141,142], This is illustrated for capsule 28 [141], where two ligands 27, each with three meta-pyridyl substituents, are connected via coordination to three palladium(II) ions. Due to the meta-substitution at the coordinating pyridyl rings, the resulting capsule 28 is helically twisted (Fig. 19). The... 

Compounds 32a-c are insoluble in non-polar solvents and in the solid state the Ln(II) centers of 32a and 32c are bound by six N-donors and exhibit trigonal antiprismatic geometries and symmetry elements [73,74], Reactivity studies of 32a have been extensive and include the reduction of unsaturated organic substrates and of d-transition metal carbonyl complexes [72], The facile oxidation of 32a is highlighted by its reaction with... 

The X-ray structure analysis of compound 2 has shown that the bismuth center is surrounded by six sulfur atoms to form a trigonal antiprismatic geometry. All three dithiocarboxylate ligands are non-equivalent and the Bi-S bonds can be divided into two types short (2.617(2), 2.626(1) and 2.647(1) A) and long (2.963(2), 3.040(1) and 3.108(2) A). One of the sulfur atom coordinates weakly to the neighboring bismuth center (3.689 A) to form a dimeric structure in the solid state [87IC1453]. 

Reduction of [Eu(OTf)(Tp )2] yielded the six-coordinate [Eu-(Tp )2] with a trigonal antiprismatic geometry and planes of the k3-TP ligands parallel to one another.615... 

Three types of bismuth atoms occur in the crystal structure of BifBijSg) , although all are Bi . Two types occur in (BiiS ) chains, and adopt five- and sk-co-ordination by sulphur atoms, with Bi-S bond lengths in the ranges 2.60— 2.94 A (five-co-ordination) and 2.63—3.13 A (six-coordination). The third type of Bi atom has a flattened trigonal-antiprismatic geometry with three Bi-S bonds of length 2.824 A and three of 3.116 A. 

The cluster Sng 4 has a monocapped square antiprismatic geometry. On the other hand, the cluster SM5 ]2, 68b, has a trigonal bipyramidal geometry, as shown by X-ray crystallography107. 

In contrast to the monoclinic tris-malonato complexes, M2(OOCCH2COO)s 8 H2O (M=Nd) which contain nonacoordinated lanthanide ions in a monocapped square antiprismatic polyhedron, the orthorhombic tris-malonates Pnma) have a tricapped trigonal prismatic geometry for the coordination polyhedron. A rep-... 

Transition Metals complex is transformed into trigonal prismatic or square antiprismatic geometry. Furthermore, the complexes tend to be labile in solution. Table 14.4 presents a summary of these differences based on properties of typical transition metal complexes. 

The anion (Fig. 33) comprises two parallel rhombs of metal atoms at an interplanar distance of 2.12 A. The two layers are staggered so as to produce an antiprismatic geometry, which may be derived from the trigonal prismatic starting material by the capping of two tetragonal faces and the breaking of the Co-Co bond common to these two faces (shown as a dotted line in Fig. 33). 

The malonate complex of Eu(III), Eu2(malonate)3 8H2O is interesting since there are two different coordination geometries, and only five of the water molecules are coordinated [167], One of the Eu ions is eight-coordinate in the form of a distorted square antiprism and the other Eu ion is nine-coordinate, distorted tricapped trigonal prism. In the analogous neodymium complex, six water molecules are coordinated because of the difference in ionic radius. The neodymium complex is nine-coordinate with monocapped antiprismatic geometry [168]. 

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