[alt-photo] Ferric ammonium citrate (fwd)

[Alberto Novo]

I have received a reply from Mike Ware off-list, and whith his permission I 
forward it and the further comments. 

Alberto
www.grupponamias.com
www.alternativephotography.com/wp/photographers/rodolfo-namias-group 

 ---------- Messaggio inoltrato ---------- 

Dear Alberto, 

I noticed your enquiry on the Alt Proc List, and since you seem not  to have 
received an adequate answer I thought I would send my  greetings and what 
information I have: 

I have the second English edition of Clerc on my shelves (1937),  and  a 
footnote on p.405 gives the formulae as (you will know where to  subscript 
the numbers!): 

green:   (C6H5O7)3Fe2(NH4)3
brown:  (C6H5O7)2H2Fe2(OH)3)(NH4). 3H2O 

As you will know, these differ somewhat from the formulae given by  Valenta 
(see p.157 of my book 'Cyanotype'). 

My third English edition of Clerc (1954) does not give any formulae  at all! 

With all good wishes, 

Mike 

Dr Mike Ware
20 Bath Road
Buxton
Derbyshire
SK17 6HH
UK 

+44 (0)1298 78604
mike at mikeware.co.uk
http://www.mikeware.co.uk 


 ----------
Dear Mike,
tank you so much! These information are what I exactly was looking for.
The green form looks like 2(Fe Citrate) + NH4 citrate, but the brown looks 
really odd.
May I forward your reply to the List?
Kind regards,
Alberto 

 ----------
Alberto -
Certainly forward it if you wish. You might add that the 'brown' formula 
could be cast in the more rational form
Fe Citrate + (NH4)H2 Citrate + Fe(OH)3 + 3H2O
but of course these formulations tell us nothing about the structure of 
these substances. The only modern structural chemistry I have come across is 
in Inorganic Chemistry, 33, (1994), 5161, where the iron (III)citrate 
complex anions are dimeric:  [Fe2(C6H4O7)2(H2O)2]2-  and  [Fe2(C6H5O7)3]3-  
which may be the photoactive dimeric species in solution.
Best wishes
Mike 

 ---------
Mike,
> You might add that the 'brown'  formula could be cast in the more rational form 
> Fe Citrate + (NH4)H2 Citrate + Fe(OH)3 + 3H2O 

I have the suspicion that these are not true formulae but the main 
components used to form the green and the brown form. Or, alternatively (for 
the brown form), what would have formed adding:
2 H3Citrate + 2 Fe(OH)3 + NH3
I know that it should be NH4OH, but NH3 keeps the resulting H2O =3 and not 
otherwise =4
I don't know what was the stoichiometry in 1930... 

Alberto