Magpie - 4-6-2008 at 22:21
I have been searching for Kf, the formation constant, for the hexafluoroferrate(III) complex, [FeF6]3- but have not had any luck. If anyone can
provide this I would much appreciate it.
12AX7 - 5-6-2008 at 03:04
I have only the first three,
Fe + F <--> FeF pKf = -6.04
FeF + F <--> FeF2 pKf = -4.43
FeF2 + F <--> FeF3 pKf = -3.15
Magpie - 5-6-2008 at 13:20
Thanks Tim. I went to the library today and found those Kf's also, but nothing higher. Perhaps they are unknown.
What got me interested in this was the use of KF as a complexing agent for Fe+++. It is specified in the qualitative analysis test for nitrogen using
sodium fusion of an organic unknown.
Edit: It is also used as a complexing agent for Fe+++ in the Group III qualitative test for Co++ to prevent the formation of [Fe(NCS)]++.
[Edited on 5-6-2008 by Magpie]
kmno4 - 5-6-2008 at 14:18
pK for Fe(3+)F(-)^6/FeF<sub>6</sub>(3-) from my tables is -16,1
[Edited on 6-6-2008 by kmno4]
chemrox - 5-6-2008 at 17:27
What book or paper did that constant come from? If you don't mind sharing the information.
kmno4 - 6-6-2008 at 06:57
This value is taken from paper book, titled "Chemical tables" (it is translation, oginal book is written in my native language), 1997 y. These tables
are the best ones I ever seen. I use it very often and all (almost) book is a set of separete pages 
.
Magpie - 6-6-2008 at 18:30
I received some NaF today so gave it a try for complexing the Fe+++ in aqueous FeCl3. If I added enough it prevented the formation of Prussian blue
upon addition of potassium ferrocyanide.