Tetragonal complexes

From the survey of coordination chemistry presented in Chapter 16, it was seen that there are numerous complexes in which the ligands lie in a square plane around the metal ion. A square planar complex can be considered as a tetragonal complex in which the ligands along the z-axis have been... 

Whereas Co, Ni and Cu11 form planar (or tetragonal) complexes with weakly bonded water molecules and are extractable into chloroform, Fe11, Zn and Mg prefer octahedral coordination and the firmly attached water in, for example, Mg0x2(H20)2 makes it hydrophilic and incapable of being solvent extracted. However, in the presence of excess oxine it, and other alkaline earth complexes, become soluble in chloroform as the water is displaced by the more hydrophobic oxine molecules. Anhydrous ZnOx2 dissolves easily in chloroform but on equilibration with water Zn0x2(H20)2 separates at the interface. 

These experimental results prompted reconsideration of the inscrutable result reported for Cu(SC5H4-p-N02)(HB(3,5-Me2pz)3) (36). The absorption spectrum of the complex was reasonably similar to that of type I copper, whereas the EPR spectrum was typical for a tetragonal complex. Because the EPR was recorded in THF at 77 K, our observa-... 

Referring to the orbital splitting pattern for an axially elongated tetragonal complex shown in Fig. 8.3.2, if we continue the elongation, the splittings... 

Nevertheless, the spectra of a number of tetragonal complexes have been interpreted to reveal both in-plane and out-of-plane ligand field strengths. 

The reliability of the data obtained in discussion of tetragonal complexes above must also be considered. In calculating the out-of-plane field strengths, Dt, as determined from the splitting of the first spin-allowed... 

A values, denoted and and Ay and respectively. The parallel component is the one coinciding with the V=0 director and the direction of the magnetic field B. In a tetragonal complex (octahedral, square pyramidal), and Ay > A. A typical... 

The properties of Type 2 copper in blue-copper oxidases contrast sharply with those of Type 1 copper in this class of enzymes. The optical (weak visible absorbance) and EPR (0.015 cm Aj <0.020 cm ) spectra clearly resemble those encountered for Cu(II) copper in low molecular weight tetragonal complexes. Despite its prosaic spectroscopy, Type 2 copper chemistry appears to be richer than that of Type 1 copper. Type 2 copper will bind exogeneous ligands at both axial and equitorial positions and is accessible to water in the solvent milieu. In blue copper oxidases, this lability to ligand exchange is used to stabilize an intermediate in the course of O2 reduction (see below). 

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