Iron (VIII)

[ferrocene2]

Some years ago, I created a topic about the existence or otherwise of iron (VIII). What follows is an update after I was able to download as a pdf all but one volume of J. W. Mellor's "A Comprehensive Treatise on Inorganic and Theoretical Chemistry". In Volume XIII Fe (Part II) on page 936 it says:

O. Baudisch and P. Mayer 2 assumed that perferric acid, FeO₃(OH)₂, or H₂FeO₄ [it means H₂FeO₅], is produced when freshly precipitated ferrous hydroxide is oxidized by oxygen. D. K. Goralevich said that iron tetroxide, or perferric anhydride, FeO₄, or perferric acid, H₂FeO₅, is probably formed as a volatile, unstable compound when barium perferrate, BaFeO₅, is treated with an excess of dil. sulphuric acid, at a low temp. Perferric anhydride is insoluble in water, but soluble in dil. acids. He prepared bright green potassium perferrate, K₂Fe0₅.nH₂0, by fusing ferric oxide with potassium hydroxide and an excess of potassium nitrate, or, better, chlorate. The salt can be purified by sublimation; it decomposes very slowly "when kept in air; explosively, when warmed, on treatment with conc. sulphuric acid, or on impact if mixed with sulphur, phosphorus, or charcoal. It is quite stable in alkaline soln., but acids readily decompose it with evolution of oxygen and, in the case of hydrochloric acid, chlorine. Oxidizing agents like chlorine and hydrogen peroxide give a deep red soln. of potassium ferrate, with evolution of oxygen. Neutral soln. of the perferrate give no reaction for ferric ions until, on the addition of acid, decomposition has commenced. Similarly with sodium perferrate, the alkaline earth perferrates were obtained as white precipitates on adding a soln. of a salt of an alkaline earth to a soln. of potassium perferrate ; with barium salt, barium perferrate, BaFeO₅.7H₂O, is produced; and with a strontium salt, strontium perferrate, SrFe0₅.7H₂0. These salts are white and insoluble in water, alcohol, and ether.

This is all it says on Fe (VIII) despite devoting six pages to Fe (VI).

Questions:

1 Does Fe (VIII) exist? If it did, one might it to be less stable than Ru (VIII) and RuO₄ isn't very stable. Going across the period from Sc - Ni, Ti (IV) and V(V) are stable, Cr (VI) less stable than Cr (III), Mn (VII) less stable than Cr (VI), and Fe (VI) pretty unstable unless dry and stored in the absence of moisture and CO2.

2 Were all these observations wrong? As I wrote previously "I remember clearly that a dark green melt was produced, that it turned white when it cooled and solidified. [I also noted that water had no obvious effect] all contrary to what Mellor said. I cannot think of any iron compound which would behave in such a way under those conditions. There are a number of iron compounds which are white, but I can't think of any which would fit this particular bill". 

3 Mellor has numerous errors. For example, it describes the properties of OsF₈ which we know doesn't exists; the perbromates and PbF₄ didn't exist according to Mellor although we know they do.

4 Is anyone in a position to try these experiments? I performed them as a teenager in 1968 when I could easily get hold of the chemicals in question.

 

[studiot]

3 hours ago, ferrocene2 said:

Some years ago, I created a topic about the existence or otherwise of iron (VIII). What follows is an update after I was able to download as a pdf all but one volume of J. W. Mellor's "A Comprehensive Treatise on Inorganic and Theoretical Chemistry". In Volume XIII Fe (Part II) on page 936 it says:

Some years ago  ?

It say you joined 3 hours ago.

 

Mellor died in 1938.

 

See the attachments for more recent history of the development of ferrocene theory including the 1973 Nobel.

Apologies for the poor quality of the scans but Greenwood and Earnshaw is a very thick book.

 

[exchemist]

3 hours ago, ferrocene2 said:

Some years ago, I created a topic about the existence or otherwise of iron (VIII). What follows is an update after I was able to download as a pdf all but one volume of J. W. Mellor's "A Comprehensive Treatise on Inorganic and Theoretical Chemistry". In Volume XIII Fe (Part II) on page 936 it says:

O. Baudisch and P. Mayer 2 assumed that perferric acid, FeO₃(OH)₂, or H₂FeO₄ [it means H₂FeO₅], is produced when freshly precipitated ferrous hydroxide is oxidized by oxygen. D. K. Goralevich said that iron tetroxide, or perferric anhydride, FeO₄, or perferric acid, H₂FeO₅, is probably formed as a volatile, unstable compound when barium perferrate, BaFeO₅, is treated with an excess of dil. sulphuric acid, at a low temp. Perferric anhydride is insoluble in water, but soluble in dil. acids. He prepared bright green potassium perferrate, K₂Fe0₅.nH₂0, by fusing ferric oxide with potassium hydroxide and an excess of potassium nitrate, or, better, chlorate. The salt can be purified by sublimation; it decomposes very slowly "when kept in air; explosively, when warmed, on treatment with conc. sulphuric acid, or on impact if mixed with sulphur, phosphorus, or charcoal. It is quite stable in alkaline soln., but acids readily decompose it with evolution of oxygen and, in the case of hydrochloric acid, chlorine. Oxidizing agents like chlorine and hydrogen peroxide give a deep red soln. of potassium ferrate, with evolution of oxygen. Neutral soln. of the perferrate give no reaction for ferric ions until, on the addition of acid, decomposition has commenced. Similarly with sodium perferrate, the alkaline earth perferrates were obtained as white precipitates on adding a soln. of a salt of an alkaline earth to a soln. of potassium perferrate ; with barium salt, barium perferrate, BaFeO₅.7H₂O, is produced; and with a strontium salt, strontium perferrate, SrFe0₅.7H₂0. These salts are white and insoluble in water, alcohol, and ether.

This is all it says on Fe (VIII) despite devoting six pages to Fe (VI).

Questions:

1 Does Fe (VIII) exist? If it did, one might it to be less stable than Ru (VIII) and RuO₄ isn't very stable. Going across the period from Sc - Ni, Ti (IV) and V(V) are stable, Cr (VI) less stable than Cr (III), Mn (VII) less stable than Cr (VI), and Fe (VI) pretty unstable unless dry and stored in the absence of moisture and CO2.

2 Were all these observations wrong? As I wrote previously "I remember clearly that a dark green melt was produced, that it turned white when it cooled and solidified. [I also noted that water had no obvious effect] all contrary to what Mellor said. I cannot think of any iron compound which would behave in such a way under those conditions. There are a number of iron compounds which are white, but I can't think of any which would fit this particular bill". 

3 Mellor has numerous errors. For example, it describes the properties of OsF₈ which we know doesn't exists; the perbromates and PbF₄ didn't exist according to Mellor although we know they do.

4 Is anyone in a position to try these experiments? I performed them as a teenager in 1968 when I could easily get hold of the chemicals in question.

 

I'm afraid I am not au fait with what may have been tried recently in this area but I'd have thought there are reasons to expect Fe VIII not to exist, chiefly the effect of increasing nuclear charge as one goes across the period which will lower the energy of the valence shell orbitals, raising the ionisation energy and pulling them in, making them less available for covalent bonding as well. How recent is the work you cite that suggests Fe VIII ?

I imagine Ru VIII and Os VIII might be expected to be similar to one another (due the effect of the lanthanide contraction on Os), and both of them to form high oxidation states more readily than Fe, due to having more diffuse (less strongly bound) valence orbitals. 

But I can't claim any practical knowledge of this. Maybe someone else here can. 

Edited September 19, 2022 by exchemist

[ferrocene2]

Studiot: I joined many years ago using the name "ferrocene". I re-joined yesterday using the name "ferrocene2" as I couldn't log-on using my previous name. And, yes, I realise that Mellor died many years ago but I first came across his work in the late sixties at Manchester Public Library (the round building) where all volumes were freely available for reference. If he was completely wrong about iron (VIII) and the perferrates - which he may well have been - can anyone explain what may have been going on or account for my own observations which were not quite the same as he described?

I am no longer in a position to repeat the experiments outlined but other people must be.

(As for the compound ferrocene itself, I studied it at (BSc) degree level in 1971-72)

[exchemist]

2 hours ago, ferrocene2 said:

Studiot: I joined many years ago using the name "ferrocene". I re-joined yesterday using the name "ferrocene2" as I couldn't log-on using my previous name. And, yes, I realise that Mellor died many years ago but I first came across his work in the late sixties at Manchester Public Library (the round building) where all volumes were freely available for reference. If he was completely wrong about iron (VIII) and the perferrates - which he may well have been - can anyone explain what may have been going on or account for my own observations which were not quite the same as he described?

I am no longer in a position to repeat the experiments outlined but other people must be.

(As for the compound ferrocene itself, I studied it at (BSc) degree level in 1971-72)

Did you have any evidence that you made an Fe compound with an oxidation state of VIII? Or was it just a mystery reaction product that was not analysed?

As far as Mellor is concerned, if he died in 1938 it seems likely that understanding of transition metal atoms and their chemistry when he was writing was less complete than today. The physics of QM only got going in the 1920s, after all, let alone its application to chemistry, and many of today's spectroscopic and other analytical techniques did not exist. 

I was at university about the same time as you and my Cotton & Wilkinson from that era says that for oxidation states of iron higher than III, "only for the states IV and VI are there substantiated reports of compounds." They go on to describe the tetrahedral, paramagnetic, ferrate ion.....  

Edited September 20, 2022 by exchemist

[ferrocene2]

I was not in a position to analyse the product - I was a schoolboy trying out on the kitchen table something I'd read which intrigued me - and still does.

I am reporting what was written in Mellor's book and what I found. Of course I'm aware that chemistry has moved on and that there are countless compounds that have been produced that people hadn't even dreamed of. And, yes, he made mistakes - some of which I mentioned previously e.g. OsF₈ doesn't exist and PbF₄ does - and so do many other transitional metal fluorides which didn't receive a mention. Who'd have predicted in the 1930s the existence of xenon compounds including some of Xe(VIII)?)

What I am asking - and have yet to receive an answer to - is what was going on in Mellor's report and what was the bright green melt in the possible (and I emphasise the word possible) equation - and I cannot think of any iron compound which could behave in this way:

5KNO₃ + Fe₂0₃ + 4KOH = 5KNO₂ + 2K₂FeO₅ + 2H₂0

If you don't know - as appears to be the case - and/or aren't in the position to try the experiments described, just say so.

I well remember Cotton and Wilkinson although I no longer have a copy. Were they aware, I wonder, of Fe (-II) and Fe (0)?

 

[exchemist]

33 minutes ago, ferrocene2 said:

I was not in a position to analyse the product - I was a schoolboy trying out on the kitchen table something I'd read which intrigued me - and still does.

I am reporting what was written in Mellor's book and what I found. Of course I'm aware that chemistry has moved on and that there are countless compounds that have been produced that people hadn't even dreamed of. And, yes, he made mistakes - some of which I mentioned previously e.g. OsF₈ doesn't exist and PbF₄ does - and so do many other transitional metal fluorides which didn't receive a mention. Who'd have predicted in the 1930s the existence of xenon compounds including some of Xe(VIII)?)

What I am asking - and have yet to receive an answer to - is what was going on in Mellor's report and what was the bright green melt in the possible (and I emphasise the word possible) equation - and I cannot think of any iron compound which could behave in this way:

5KNO₃ + Fe₂0₃ + 4KOH = 5KNO₂ + 2K₂FeO₅ + 2H₂0

If you don't know - as appears to be the case - and/or aren't in the position to try the experiments described, just say so.

I well remember Cotton and Wilkinson although I no longer have a copy. Were they aware, I wonder, of Fe (-II) and Fe (0)?

 

OK fair enough then: I don't know. But I guarantee it was not an Fe VIII compound. 

Maybe @John Cuthber will have a comment. He seems to be the best on inorganic chemistry that we have on this forum. I was hoping this discussion might bring him out of the woodwork, but anyway this will now ping him whenever he next logs in.

Edited September 21, 2022 by exchemist

[John Cuthber]

On 9/19/2022 at 6:53 PM, ferrocene2 said:

K. Goralevich said that iron tetroxide, or perferric anhydride, FeO₄, or perferric acid, H₂FeO₅, is probably formed as a volatile, unstable compound when barium perferrate, BaFeO₅, is treated with an excess of dil. sulphuric acid, at a low temp.

Where does one get the BaFeO5 from?
It's hard enough to get 

https://en.wikipedia.org/wiki/Barium_ferrate
And someone is suggesting taking another couple of electrons of the iron.

I don't doubt the existence of Fe 8+ ions in the sun, but I don't imagine they have any chemistry.

Much as I like reading old textbooks, I don't always accept their claims at face value.
The difficulty with doing analysis to determine the oxidation state of the iron would be great today and I simply don't think they would have been able to guarantee accuracy back then. (This might be one of the examples of Mossbauer spectroscopy actually being useful.)

Certainly the WIKI page doesn't say anything about Fe(VIII)
https://en.wikipedia.org/wiki/High-valent_iron

55 minutes ago, ferrocene2 said:

I well remember Cotton and Wilkinson although I no longer have a copy. Were they aware, I wonder, of Fe (-II) and Fe (0)?

 

They were. I have a copy from 1962. It mentions the carbonyl complexes as examples.

[exchemist]

5 hours ago, ferrocene2 said:

I was not in a position to analyse the product - I was a schoolboy trying out on the kitchen table something I'd read which intrigued me - and still does.

I am reporting what was written in Mellor's book and what I found. Of course I'm aware that chemistry has moved on and that there are countless compounds that have been produced that people hadn't even dreamed of. And, yes, he made mistakes - some of which I mentioned previously e.g. OsF₈ doesn't exist and PbF₄ does - and so do many other transitional metal fluorides which didn't receive a mention. Who'd have predicted in the 1930s the existence of xenon compounds including some of Xe(VIII)?)

What I am asking - and have yet to receive an answer to - is what was going on in Mellor's report and what was the bright green melt in the possible (and I emphasise the word possible) equation - and I cannot think of any iron compound which could behave in this way:

5KNO₃ + Fe₂0₃ + 4KOH = 5KNO₂ + 2K₂FeO₅ + 2H₂0

If you don't know - as appears to be the case - and/or aren't in the position to try the experiments described, just say so.

I well remember Cotton and Wilkinson although I no longer have a copy. Were they aware, I wonder, of Fe (-II) and Fe (0)?

 

By the way, didn't Geoffrey Wilkinson get his Nobel Prize for his work on organometallics, including ferrocene? If so, who better to know the unconventional (formal) oxidation states that can be involved?  

[ferrocene2]

If it wasn't iron (VIII) in the accounts above (see post of Monday at 6.35) then what was it?

In the original post, I quote Mellor who describes how (what he says was) barium perferrate and the other iron (VIII) compounds were obtained.

I've said numerous times in these exchanges that there are many mistakes in Mellor's work (but Wikipedia isn't error free either).