Formation of complexes by ferric ions is more frequent than ferrous ions. Why?

Looking at the electronic configurations of ferrous and ferric ions they are d6 and d5 systems respectively. Hence, ferric ions are more stable. But in octahedral complexes like hexathiocyanates, the electron count of ferric ions reaches only 17 while for ferrous it reaches 18. In the case of thiocyanate , ferric complexes with the ligands while ferrous does not react at all.


