Copper trigonal bipyramidal complexes

Large numbers of five-coordinate copper(II) complexes in several stereochemistries are known. The spectra which have been most studied with a view to interpretation are those of the trigonal bipyramidal complexes, for which assignments have been proposed on the basis of molecular orbital, angular overlap, and crystal-field models. 

In contrast, the major Cu species in hydrated K-X is clearly coordinated to three waters and can be assigned as Cu jj in site SII. Partial dehydration at 30-60° C converts Cujjj to the trigonal bipyramidal complex, Cujj. Rehydration at room temperature converts most of the Cujj to Cum hut traces of the former are still present. Cum becomes the sole copper species on dehydration at 400° C and rehydration at room temperature. Complete dehydration at 400° C gives the same species as formed in Na-X which is assigned to Cuq in site SI. ... 

Rana and Teotia 116) have reported the synthesis of a novel tridentate macrocycle 136 by the reaction of 2,6-dipicolinic acid hydrazide and acetylacetone in the presence of cobalt(II), nickel(II), and copper(II) salts. As is frequently the case, water occupies the axial positions of these trigonal bipyramidal complexes and the chelating nitrogen atoms are essentially coplanar. 

A series of copper(II) complexes with ring-substituted phen-ligands have been synthesized and their molecular structural and electronic structural properties have been investigated.246 Each structure ((280) r = 0.72, (281) r = 0.81, (282) r = 0.88, (283) r = 0.83, and (284) r = 0.68) is characterized by a distorted trigonal-bipyramidal arrangement of ligands around copper. 

The pyrazole phosphazine ligand, hexakis(3,5-dimethylpyrazolyl)cyclotriphosphazene (16) forms a dizinc complex, that has been structurally characterized, and the analogous copper zinc complex.158 Two ZnCl2 units are coordinated, one distorted tetrahedral and one distorted trigonal-bipyramidal, separated by 7.51 A. Cu1 and ZnCl2 can also be coordinated giving a heteronuclear compound with a Zn Cu separation of 6.798 A. 

Although only four examples of trigonal bipyramidal copper(II) complexes have been studied in the literature so far, these investigations have shown that substitution generally occurs via an 7a mechanism with a six-coordinate transition state. In the case of the Me6tren complex, the steric hindrance prevents the formation of a six-coordinate transition state. The consequence is a dramatic reduction in la-mechanistic changeover toward an 7d mechanism. It... 

In general, it is not possible to predict the stereochemistry about the separate copper(II) ions in most cases they are the same and may or may not be related by a centre of symmetry. The actual stereochemistries produced are recognizably the same as those occurring in mononuclear copper(II) complexes (Figure 19.1). The most common is that of square-based pyramidal with rhombic coplanar, compressed tetrahedral, trigonal bipyramidal and elongated rhombic octahedral stereochemistries all occurring. 

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