[xshadow]

Hi
I have a doubt

I've studied that for group 13,14,15 the high oxidation states become less stable when we go down a group...this is due to the inert doublet effect (relativistic effect)

Now for transition metal I've read the opposite...the haviest transition metals (5d serie) have  the high oxidation state that are much more stable compared with the series 1 and 2


Also the ionization energy for the third transition serie is higher than the first two series....highest oxidation states  should be more difficult to reach for heavy transition metal because  bigger I.E.  !!!   
What is the  reason for this trend??
thankss