Second-order rate constant for the reaction between $[Co(NH_3)_5X]^{n+}$ ($n = 3$ for $X = NH_3$ and $H_2O$; $n = 2$ for $X = Cl^-$) and $[Cr(H_2O)_6]^{2+}$ at room temperature varies with the $X$ as
The given problem involves determining the order of the second-order rate constant for the reaction between complexes of the form \([Co(NH_3)_5X]^{n+}\) and \([Cr(H_2O)_6]^{2+}\), where the ligand \(X\) changes. We need to evaluate how the second-order rate constant varies with different ligands: \(NH_3\), \(H_2O\), and \(Cl^{-}\).
Let's consider what affects the rate of such reactions:
- The lability of the ligand \(X\) in the complex affects how readily it can be replaced. The more labile the leaving group, the higher the rate constant for its involvement in a reaction.
- Leaving group ability is influenced by factors such as charge, size, and the type of interactions it forms with the central metal ion.
Let’s analyze each case:
- \(Cl^{-}\) is a very commonly known good leaving group due to its ability to stabilize the negative charge effectively when it leaves, and it forms weaker interactions with the central metal compared to other ligands like \(NH_3\).
- \(H_2O\) is a polar ligand and has moderate leaving group ability due to its ability to form hydrogen bonds and its neutral charge.
- \(NH_3\) is a strong field ligand which strongly binds to metals, making it a poor leaving group.
Based on these observations, the expected order of reactivity with \([Cr(H_2O)_6]^{2+}\) based on the lability of the ligand \(X\) is:
\(Cl^{-} \gt H_2O \gt NH_3\)
Thus, the correct answer is: \(Cl^- \gt H_2O \gt NH_3\), which corresponds to the option correctly providing this order.
Important Questions from Electron Transfer Reactions
Consider the following statements for the self‐exchange electron transfer reaction in [Cr(H2O)6]2+/3+
a. σ* orbitals are only involved in electron transfer
b. It involves large inner‐sphere reorganization energy
c. It involves no change in M–L bond lengths
d. Rate of self‐exchange electron transfer is fast
The correct statements are
In 3‐iron ferredoxins, the number of sulfide bridges and cysteinyl ligands, respectively, are:
The second order rate constants for the outer sphere self- exchange electron transfer reactions for [Ru(NH3)6]2+/[Ru(NH3)6]3+ and [Co(NH3)6]2+/[Co(NH3)6]3+ are 9.2 × 102 M-1 sec-1 and ≤ 10-9 M-1 sec-1, respectively.
The correct rationale for the above data is
In the following electron transfer reactions, the one in which the bridging ligand comes from the reductant is
Of the following assertions regarding the mechanism of electron transfer,
A. An outer-sphere mechanism involves electron transfer from the reductant to the oxidant, with the coordination shells or spheres of each staying intact.
B. In the inner-sphere mechanism, the reductant and oxidant share a ligand in their inner or primary coordination sphere which assists in electrons being transferred.
C. In the inner-sphere mechanism, an oxidant possesses at least one ligand capable of binding simultaneously to two metal ions.
D. In the inner-sphere mechanism, ligands of reductant are substitutionally inert.
The correct statements are
