Metal coordination geometry

In 1937 Jahn and Teller applied group-theoretical methods to derive a remarkable theorem nonlinear molecules in orbitally degenerate states are intrinsically unstable with respect to distortions that lower the symmetry and remove the orbital degeneracy.37 Although Jahn-Teller theory can predict neither the degree of distortion nor the final symmetry, it is widely applied in transition-metal chemistry to rationalize observed distortions from an expected high-symmetry structure.38 In this section we briefly illustrate the application of Jahn-Teller theory and describe how a localized-bond viewpoint can provide a complementary alternative picture of transition-metal coordination geometries. 

Figure 13 Common transition metal coordination geometries.

In order to answer some of these outstanding questions, this chapter presents and analyzes a variety of chiral architectures based on metal-ligand coordinative interactions. Although there are a number of ways in which chirality can be introduced into coordination assemblies [2], we will concentrate on ensembles formed from achiral components, where chirality arises from metal coordination geometries or asymmetric ligand arrangements. Particular focus lies with assemblies that show host-guest encapsulation potential and maintain their chirality in solution. 

Monodentate ligands directing of hydrogen bond formation by metal coordination geometry... 

Solids with octahedral, tetrahedral, square planar, and linear metal coordination geometries, including many different types of polyhedra connectivity modes, are amenable to dimensional reduction. Tulsky and Long compiled an enormous database of over 300 different allowed combinations of M and X and over 10,000 combinations of A, M, and X. The formalism may be extendable to quaternary phases as well. However, frameworks containing anion-anion linkages, anions other than halides, oxide, or chalcogenides, nonstoichiometric phases, and mixed-valence compounds were excluded from their initial study. 

Metal coordination geometry and ligand environment via analysis of vibrational frequencies. 

The cascade reaction for the preparation of anilines is particularly well suited to the synthesis of potential ligands, as is illustrated by the scorpion ligand A,A-4-tris(pyridin-2-ylmethyl)aniline (37), which forms a range of Cu complexes with widely varying solid-state structures.Clearly, from the metal coordination geometries illustrated in Figure 6.9, Horning-crown macrocycles may fulfill similar roles. 

Table 20-1 Comparison of metal coordination geometry in different metal-substituted desulfor-edoxins...

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