Lecture_6_Isomerism

Lecture_6_Isomerism - Chem 310 Lecture Module 6 Isomerism...

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Chem 310 Lecture Module 6 Isomerism
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Linkage isomerism •Some ligands may form M-L bonds with different atoms. Examples: NO 2 - may be N- onded ( itro orO onded ( itrito SCN - ay be S onded (thiocyanato) or N onded bonded ( nitro ) or O-bonded ( nitrito ); SCN may be S-bonded (thiocyanato) or N-bonded (isothiocyanato); CO could be O bonded or C bonded (but its always C –bonded). History of the nitro / nitrito problem of Jörgenson: ONO - NO 2 was assigned by Jörgenson nearly 100 years ago based on colors of related complexes. The red isomer slowly converts into the yellow form. However, in the past the assumption of O- and N-bonding was questionable; some researchers tried to argue that the red solution contains unreacted starting material. Adell investigated the kinetics and found out that the conversion reaction was 1 st order, i.e. the rate depends lely on the concentration of the complex hint to the existence of the itrito mplex If the red isomer solely on the concentration of the complex - a hint to the existence of the nitrito complex. If the red isomer was unreacted starting material, the reaction should be 2 nd order, depending on the concentration of the complex and the nitrite ion:
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18 O experiment: Nitrito complex forms without rupture of the Co-O bond of the hydroxo complex. Best planation: explanation: Upon conversion into the nitro form, the 18 O remains part of the NO 2 - ligand, indicating an intramolecular reaction (which confirms 1 st order): Removal of 18 O is possible by hydrolysis of the nitro isomer:
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Thiocyanate/isothiocyanate linkage isomerism •Square planar Pt II complexes: the different linkages can be understood based on the ifferent onding abilities; only the S atom may participate in onding Note that N different π bonding abilities; only the S atom may participate in π bonding. Note that N bonds are linear and S bent.
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Lecture_6_Isomerism - Chem 310 Lecture Module 6 Isomerism...

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