Coordination compounds preferred geometries 68

TABLE 2.10 Preferred Geometries in Simple Coordination Compounds ... 

From the results obtained for the model species 3, it is concluded that the TBP, with oxygen atoms in the axial positions, is the energetically preferred geometry of the Si coordination polyhedra of the title compounds. As the pseudorotation according to path 1 needs only a small amount of energy, package effects in the crystal (which are individual for each compound) can easily cause distortions of the TBP toward the SP. This assumption is in agreement with the results obtained in experimental studies [1]. 

The crystal packing of organomagnesium compounds has shown that intramolecular coordination is preferred over solvent coordination. These compounds have a tetrahedral geometry. The crystal structure of [MeO(CH2)4]aMg [Compound 27] indicates that the... 

A representative compound that utilizes pyrazole dicarboxylate to produce a 2-dimensional, U(VI)/Cu(II) compound is U02Cu(C5H2N204)2(H20)2 (Figure 23). Here the U02 center is in square bipyramidal geometry with four monodentate carboxylate oxygen atoms from four distinct linker molecules. Cu(II) is coordinated to two bidentate N/0 donors and two H2O groups to yield an overall octahedral geometry. Coordination site preferences can be seen in this compound as the uranyl cation is bound strictly to... 

The concepts rely also on our understanding of preferred coordination numbers and geometries. For example, for many metal ions six-coordination is common, but some stable examples of both five- and seven-coordination are known. Therefore, it isn t too much of a jump to consider a short-lived five- or seven-coordinate species existing for a species stable only in six-coordination - in other words, a transition state of lower or higher coordination number. As an example, six-coordinate octahedral is the overwhelmingly dominant coordination mode for stable cobalt(ni) complexes. Yet, in recent years, rare examples of isolable but usually very reactive compounds with five-coordination and seven-coordination have been prepared. It doesn t take too much of an act of faith to assert that such geometries form as short-lived transition state species in substitution reactions of this whole family of complexes. 

Using data from Table 16.4, calculate the CFSEs for every d" configuration in both the tetrahedral (always HS) and square pyramidal geometries. Explain why LS d coordination compounds will always prefer the square planar geometry. 

Tetraorganoantimony(V) alkoxides and triorganoantimony(V) dialkoxides are monomeric, five-coordinate compounds, e.g. PluSbOMe and Ph3Sb(OMe)2 [420]. This is not surprising, because the trigonal bipyramidal geometry found in these compounds is a preferred coordination mode of antimony(V). Despite this, tri-phenyl(4-nitrocatecholato)antimony(V) was found to dimerize via Sb- - -O second-... 

---