Trigonal bipyramidal geometry, copper

Finally, we examine azurin, a blue protein (FW = 14 000) devoted to bacterial electron transport, the copper centre of which has a penta-coordinate trigonal bipyramidal geometry, at variance with all the other cupredoxins, Figure 39.73... 

Fig. 3. Geometries of the type 1 copper sites of various blue copper proteins. The trigonal planar geometry is the type 1 site of laccase from Coprinus cinereus (PDB Code 1A65). The trigonal bipyramidal geometry shown is the copper site of azurin from Pseudomonas aeruginosa (PDB Code lAZU). The trigonal pyramidal/distorted tetrahedral sites are of the stellacyanin from Cucumis sativus (PDB Code IJER), NNSO site, and of the plastocyanin from Populus nigra (PDB Code IPLC) NNSS site.

There are several reasons for the extensive use of copper Lewis acids in stereoselective transformations (i) predictable coordination geometry about the metal, (ii) ready availability, (iii) two oxidation states, and (iv) moderate Lewis acidity. Copper(II) complexes usually adopt a square planar, square pyramidal, or trigonal bipyramidal geometry, whereas Cu(I) complexes have a preference for tetrahedral geometry (Figure 1). 

The Near-IR/vis absorption spectrum of complex 73 in water-NaOH solution was fully consistent with a trigonal-bipyramidal geometry of the copper(II) ion and the EPR spectrum is in agreement with a five-coordination sphere with the cation bound to the four nitrogen atoms of the tren unit and to one solvent molecule, a structure similar to that proposed for the parent complex 71 soluble in organic solvents. Thus it appears that the water solubilization retains the geometry of the complex around the metal center, but it was found that the redox properties were... 

---