Octahedral geometry electronic structures

Type II copper enzymes generally have more positive reduction potentials, weaker electronic absorption signals, and larger EPR hyperfine coupling constants. They adopt trigonal, square-planar, five-coordinate, or tetragonally distorted octahedral geometries. Usually, type II copper enzymes are involved in catalytic oxidations of substrate molecules and may be found in combination with both Type I and Type III copper centers. Laccase and ascorbate oxidase are typical examples. Information on these enzymes is found in Tables 5.1, 5.2, and 5.3. Superoxide dismutase, discussed in more detail below, contains a lone Type II copper center in each of two subunits of its quaternary structure. 

The first hydride examined was naturally Os(CO)4H2. The cis structure presumed for this compound (and for all the other ( (CO RR ) from ir data was confirmed by Raman observation (methylcyclohexane solution) of os-h at 1971 (A i) and 1942 (B2) cm-1 and by an electron diffraction study on the compound in the gas phase (17). The structure departs only slightly from octahedral geometry, with the CO (axial)-Os-CO-(equatorial) angle being 96.3 0.7°. The structure of the Os(CO)4 unit is similar to those of the same units in Os3(CO)i2 (18). 

Porphyrin (8) and phthalocyanine complexes stabilize a square planar structure, probably as a result of extensive electron delocalization. Square planar complexes often give paramagnetic bis adducts with a Irans octahedral geometry. 

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