The fac and mer Isomers of Transition Metal Complexes

In this section we will show how symmetry analysis can help decipher the spectrum by determining how many bands to expect for a given molecular geometry. This allows us to distinguish between possible isomers. For example, the general six-coordinate complex ML3(C0)3 can occur in one of two isomeric forms  

The analysis of the /flc-isomer is identical to the ammonia N—H stretching modes example of Section 6.6.2, so that the three basis vectors give rise to three vibrational modes with irreducible representations  

For the C2V case we have found three irreducible representations, all of which are IR active. 

Problem 6.17 For the C2., isomer, the basis vectors bi and 2 are symmetry related. Use the projection operator method to show that the Ai and B2 SALCs have the form 

The C=0 bond on the C2 axis, with basis vector bs, is separate from bi and 2 because it is not exchanged with them by any of the symmetry operations, b lies on the symmetry axis, so it can only have an Ai representation. This means it can only be involved in linear combinations with the Ai function found for the bi and 2 set, i.e. 

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