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General Chemistry Principles, Patterns, and Applications, 2011

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Replacing another A lig<strong>and</strong> by B gives an MA3B3 complex for which there are also two possible isomers. In<br />

one, the three lig<strong>and</strong>s of each kind occupy opposite triangular faces of the octahedron; this is called<br />

the fac isomer (for facial). In the other, the three lig<strong>and</strong>s of each kind lie on what would be the meridian if<br />

the complex were viewed as a sphere; this is called the mer isomer (for meridional):<br />

E X A M P L E 6<br />

Draw all the possible geometrical isomers for the complex [Co(H 2O) 2(ox)BrCl] − , where ox is − O 2CCO 2− , which<br />

st<strong>and</strong>s for oxalate.<br />

Given: formula of complex<br />

Asked for: structures of geometrical isomers<br />

Solution:<br />

This complex contains one bidentate lig<strong>and</strong> (oxalate), which can occupy only adjacent (cis) positions, <strong>and</strong><br />

four monodentate lig<strong>and</strong>s, two of which are identical (H 2O). The easiest way to attack the problem is to go<br />

through the various combinations of lig<strong>and</strong>s systematically to determine which lig<strong>and</strong>s can be trans. Thus<br />

either the water lig<strong>and</strong>s can be trans to one another or the two halide lig<strong>and</strong>s can be trans to one another,<br />

giving the two geometrical isomers shown here:<br />

Saylor URL: http://www.saylor.org/books<br />

Saylor.org<br />

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