Octahedral complexes containing period 5 or 6 metal centers, or high oxidation n
ID: 975339 • Letter: O
Question
Octahedral complexes containing period 5 or 6 metal centers, or high oxidation numbers, are less kinetically labile than complexes of period 4 metals or metals with lower oxidation numbers. Assuming these reactions proceed via a dissociative mechanism, select the reason for this. Select all that apply.
a. Period 5 and 6 d-block metals form stronger metal–ligand bonds than period 4 d-block metals.
b. Metal ions with high oxidation numbers form stronger bonds to ligands than metal ions with low oxidation numbers.
c. Metal ions with low oxidation numbers form bonds to ligands that have more covalent character than those formed by metal ions with high oxidation numbers.
d. Period 5 and 6 d-block metals have larger ionic radii than period 4 d-block metals, resulting in a sterically crowded transition state.
Explanation / Answer
Ans:
a. Period 5 and 6 d-block metals form stronger metal–ligand bonds than period 4 d-block metals.
b. Metal ions with high oxidation numbers form stronger bonds to ligands than metal ions with low oxidation numbers.
If ligand substitution takes place by a d mechanism, the strength of the metal-leaving group bond is directly related to the substitution rate. Metal centers with high oxidation numbers will have stronger bonds to ligands than metal centers with low oxidation numbers. Furthermore, period 5 and 6 metals have stronger metal ligand bonds Therefore, for reactions that are dissociatively activated, complexes of period 5 and 6 metals are less labile than complexes of period 4 metals, and complexes of metals in high oxidation states are less labile than complexes of metals in low oxidation states.
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