# Variable oxidation state of transition metal ions

Transition metals can form stable ions with different oxidation states. But I am confused why doesn't only the most stable state exist. Let me clarify my question more:

$$\ce{Ti^{2+} -> Ti^{3+} + e^-}$$ With $E^0 = +0.5~\mathrm{V}$.

This just shows that $\ce{Ti^{3+}}$ is more stable. So my question is that why doesn't $\ce{Ti^{3+}}$ only exist in its most stable form?

• Understanding Latimer, Pourbaix and Frost diagrams might help you understand the relative interconversion of different oxidation states. here and here is a good link. I will post an answer if you still want any clarifications. – Satwik Pasani Feb 9 '14 at 10:59
• if you look at the electron configurations of the Titanium cations you can see what is stable (titanium 4+ is most stable because it has the same electron configuration as Argon) and Ti(3+) has a half filled 4s-orbital and is relatively stable... – user2117 Feb 9 '14 at 13:52

Thermodynamics proposes, kinetics disposes. The most stable form can have a high activation energy barrier surrounding it. The medium matters. Hard Lewis bases (water) stabilize high oxidation states (Cu(II), tungstate). Soft Lewis bases (acetonitrile) stabilize low oxidation states (Cu(II); $\ce{W(CO)6}$ and http://www.google.com/patents/EP1995347A1?cl=en).
$\ce{Ti^{+4}}$ is the basement, especially with oxygen. Now rationlalize titanium suboxide Magnéli phases. They are spectacular as inert electrodes under extreme conditions, re Ebonex.