[francesco]

 When I was studyng difference in group 12 on Greenwood Chemistry of the Elements I was in doubt. I read:

"The increasing polarizing power and covalency of their compounds in the sequence, Mg(II) < Zn(II) < Cd(II)  < Hg(II), is a reflection of the decreasing nuclear shielding and conseguent increasing of power distortion in the sequence: filled p shell < filled d shell < filled f shell"

 I've not understood the nature of power of distortion and I think that the  reason of stability of Hg-C bond is the major softness character of Hg in respect to Cd and Zn. And f orbital are not innerer than d orbital? Why I'm wronging?      And I've read in
Henry Strasdeit Angew. Chem. Int. Ed. 2001, 40(4) 707 "Nevertheless, the enzyme activities here are significantly reduced as well, probably because the less Lewis acidic Cd(2+) ion has a weaker polarizing effect on its environment. Can you explain me?
I'm very grateful! Scuse me for my bad english?
F. O.