Rank the following complex ions in order of increasing wavelength of light absorbed. (Use the appropriate <, =, or > symbol to separate substances in the list.)
Co(H2O)63+, Co(CN)63-, CoI63-, Co(en)33+
To rank the complex ions in order of increasing wavelength of light absorbed, we need to consider the ligands and their respective spectrochemical series. In general, the nature of ligands determines the wavelength of light absorbed by a complex ion.
1. Co(H2O)63+: This complex ion has water (H2O) as a ligand. Water is a weak field ligand and is known to absorb light in the visible region of the electromagnetic spectrum. Therefore, it absorbs light with a shorter wavelength compared to other ligands.
2. Co(CN)63-: Here, cyanide (CN-) acts as a ligand. Cyanide is a strong field ligand, leading to greater splitting of the d-orbitals of the central metal ion. Consequently, the absorption of light occurs at a longer wavelength compared to water ligands.
3. CoI63-: Iodide (I-) ions are the ligands in this complex. Similar to cyanide, iodide is also considered a strong field ligand. Thus, the complex absorbs light at an even longer wavelength compared to cyanide complexes.
4. Co(en)33+: In this complex ion, ethylenediamine (en) is the ligand. Ethylenediamine is a bidentate ligand that forms a chelate complex with the central metal ion. It is considered a stronger field ligand than water, but weaker than cyanide and iodide. Consequently, the absorption of light occurs at a longer wavelength than water but shorter than cyanide and iodide complexes.
Ranking the complex ions in order of increasing wavelength of light absorbed:
Co(H2O)63+ < Co(en)33+ < Co(CN)63- < CoI63-