# Energy diagram of copper iodide complex

We did an experiment where copper iodide 4-methylpyridine and copper iodide imidazole was formed and now we are asked what orbital the electron is excited from and to.

After much research we still struggle to answer this question. We came to the conclusion that the structure of our two products are tetrahedral and thus the electron should be excited from $$\mathrm{e_g}$$ to $$\mathrm{t_{2g}}$$. However, since copper is a $$\mathrm{d^{10}}$$ metal, isn't the $$\mathrm{t_{2g}}$$ orbital full? So, to which orbital would the electron be excited? Have we misunderstood anything?

All help as well as links to helpful information is much appreciated!