Which of the following octahedral complexes absorbs the photon with the longest wavelength, λ? I wonder which of the following absorbs photons with the longest wavelength, $\ce{[Cr(CN)6]^3-}$, $\ce{[Cr(SCN)6]^3-}$ and $\ce{[Cr(H2O)6]^3+}$.
I know the one to absorb the highest wavelength should also have the highest spin. Since all of these are coordination isomers, I think the strong-field ligands should have higher energies (making the answer $\ce{[Cr(CN)6]^3-}$).
I hope someone can clarify the relation between ligand field strength and energy. Any help is much appreciated!
Since CN- is a strong field /pi-acceptor ligand, therefore, it will create larger splitting. So for transition higher energy will be needed. It means that in case of Complexes with CN- higher energied photons i.e. photons with shorter wave length will be absorbed.