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As the title states, I'm wondering why the $\ce{[CrO4]^2-}$ and $\ce{[MnO4]-}$ ions display different colors in solution. Both of the metal ions have a $\mathrm{d}^0$ electron configuration, have the same ligands, yet their respective absorption spectra max out about $100\mathrm{~nm}$ apart, with the chromium complex absorbing at the shorter wavelength of $420\mathrm{~nm}$, and the manganese absorbing at $526\mathrm{~nm}$.

What causes this difference?

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    $\begingroup$ chemistry.stackexchange.com/questions/39829/… Put very simply, the energy gap $\Delta E (= h\nu)$ between the $e$ and $t_1$ orbitals is different. And this difference stems from the fact that the "$\ce{Cr^6+}$" ion has d orbitals that are higher in energy than those of "$\ce{Mn^7+}$". $\endgroup$ – orthocresol♦ Oct 29 '15 at 18:52

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