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Question
Which of the following is the correct order of increasing field strength of ligands to form coordination compounds?
Options
\[\ce{SCN^- < F^- < C_2O^{2-}_4 < CN^-}\]
\[\ce{SCN^- < F^- < CN^- < C_2O^{2-}_4}\]
\[\ce{F^- < SCN^- < C_2O^{2-}_4 < CN^-}\]
\[\ce{CN^- < C_2O^{2-}_4 < SCN^- < F^- }\]
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Solution
\[\ce{SCN^- < F^- < C_2O^{2-}_4 < CN^-}\]
Explanation:
The ligands can be ranked based on their field strength, which refers to how strongly they affect the splitting of the metal’s d-orbitals in a coordination complex. The field strength of ligands is largely determined by their ability to donate electrons and interact with the metal ion. Stronger field ligands create a larger splitting of d-orbitals (larger Δ), which typically leads to a low-spin complex.
Order of Field Strength:
- SCN− (thiocyanate): This is a weak field ligand.
- F− (fluoride): Slightly stronger than SCN− but still a weak field ligand.
- \[\ce{C_2O^{2-}_4}\] (oxalate): A moderately strong field ligand, stronger than F−.
- CN− (cyanide): A very strong field ligand, capable of causing the largest splitting of d-orbitals.
Thus, the correct order is:
\[\ce{SCN^- < F^- < C_2O^{2-}_4 < CN^-}\]
