What is the configuration of dimethyl[tris(trifluoromethyl)]-λ⁵-phosphane? I know that $\ce{(CH3)2P(CF3)3}$ is geometry of trigonal bipyramid and according to Bent's rule $\ce{CH3}$  goes to axial positions and $\ce{CF3}$s remains on equatorial positions. However, as per Bent's rule more electronegative ligand goes to axial position.

Now my question is how to determine which is more electronegative between $\ce{CH3}$ and $\ce{CF3}$?
You can note that $\ce{-CH3}$ shows electron releasing (+I) effect while $\ce{-CF3}$ shows strong electron withdrawing effect. Now, you can treat inductive effect as the organic analogue of electronegativity, giving axial positions to $\ce{-CF3}$  and equatorial ones to $-\ce{CH3}$ in accordance with Bent's rule.