Question

How do I know which transition metal complex is most stable?

Answer 1

`"How do you compare apples and oranges.......?"`

Explanation:

I take it, and I fully accept that I may be wrong, that your question relates to ligand field theory, and the electronic configuration of a transition metal ion in an octahedral coordination complex......

You know that that when a transition metal ion is in octahedral coordination, the ligand field strongly differentiates between axial and non-axial `"d-orbitals"`. For octahedral coordination, this occurs for `d^4, d^5,` `d^6`, and `d^7` metal ions, which can generate low spin (differentiation between `t_"2g"` and `e_g` is large), and high spin (differentiation between `t_"2g"` and `e_g` is small) complexes.

Half-filled d-orbitals, `d^5`, and fully-filled d-orbital configurations, `d^10`, tend to have a special stability, but for each scenario it is hard to find a metric with which to make meaningful comparison.