The compound Ni(H2 O)6 Cl2 is green, whereas Ni(NH3)6 Cl2 is violet. Predict the predominant col

step 1 Now the question is, the compound nickel water 6 CL2 is green whereas nickel NH36 CL2 is violet.

The compound Ni(H2 O)6 Cl2 is green, whereas Ni(NH3)6 Cl2 is...

The compound $\mathrm{Ni}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6} \mathrm{Cl}_{2}$ is green, whereas $\mathrm{Ni}\left(\mathrm{NH}_{3}\right)_{6} \mathrm{Cl}_{2}$ is violet. Predict the predominant color of light absorbed by each compound. Which compound absorbs light with the shorter wavelength? Predict in which compound $\Delta$ is greater and whether $\mathrm{H}_{2} \mathrm{O}$ or $\mathrm{NH}_{3}$ is the stronger field ligand. Do your conclusions agree with the spectrochemical series?

Key Concepts

Complementary Colors in Transition Metal Complexes

The perceived color of a transition metal complex is due to the wavelengths of light that are transmitted or reflected after selective absorption during electronic (d-d) transitions. The color observed is typically the complement of the color of light absorbed. Hence, if a complex appears green, it generally absorbs light in the red region, and if it appears violet, it absorbs light in the yellow-green region. This concept is crucial to understanding the relationship between the electronic transitions dictated by ? and the resulting color of the complex.

Spectrochemical Series

The spectrochemical series is an empirically derived list that ranks ligands from weak-field to strong-field based on the magnitude of crystal field splitting they produce. Ligands found toward the strong-field end cause larger splittings in the d-orbitals, affecting the color displayed by the complex because the light absorbed, which is complementary to the observed color, shifts depending on ?.

Crystal Field Theory

Crystal field theory explains the splitting of the degenerate d-orbitals in transition metal complexes when ligands approach the central metal ion. In an octahedral complex, the five d-orbitals split into two groups (t2g and eg) due to the electrostatic interactions with the ligands. The energy difference between these sets of orbitals, denoted as ? or 10Dq, is key in determining many properties of the complex, including the wavelengths of light absorbed during d-d transitions.

Ligand Field Strength

Ligand field strength reflects the ability of a ligand to induce splitting in the d-orbitals of the central metal ion. Strong-field ligands produce a larger splitting (larger ?) while weak-field ligands cause a smaller splitting. The magnitude of ? influences the energy and wavelength of light absorbed; larger ? typically means absorption of higher-energy (shorter wavelength) light.

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