I've been doing a bit of vanadium chemistry lately, and decided to experiment with making ferrocyanides of vanadium to see what they look like. I made
one that I believe to be vanadyl ferrocyanide, although I am not completely sure. I prepared it by adding a solution of sodium ferrocyanide to a
solution of vanadyl sulfate prepared from reducing vanadium pentoxide with sodium metabisulfite. This resulted in the precipitation of a forest green
compound and the solution going colorless. I vacuum filtered this and rinsed it with distilled water a few times, and then put it in my desiccator to
dry. I removed it this morning, and found that the cake had shrunk up into one solid piece, and was quite hard. I was able to snap it in half and it
broke cleanly, leaving a smooth, glossy surface where it was broken. It appears to be black in color now that it has dried, although when some is
ground into a powder, it is clear that it is really still the original green color. I'll post a picture later.
Now what I would like to know is what this compound really is. Vanadyl ferrocyanide seems reasonable to me, since vanadyl is neither oxidizing nor
reducing, so it is unlikely to be a ferricyanide or a salt of a different vanadium oxidation state, but at the same time, I don't know for sure, and
there is practically nothing on the internet about it currently. After some digging I was able to come up with a couple of references that are both
over 100 years old and not of much help. One was to a green "vanadium ferrocyanide" (very non-specific) that was used sometimes for old timey color
photography toning, and the other was a single line in a reference book that noted only that vanadyl ferrocyanide exists and it is insoluble.
This may explain to you about the colored ferrocyanides. Vanadyl ion forms a nice green compound with ferrocyanide.
Ah, thank you woelen. I'm surprised that didn't come up on my search. That makes me feel much more confident that what I have made
is indeed vanadyl ferrocyanide. I will do some more experiments with it. Also, I found a different vanadium ferrocyanide that is a dark red color. It
formed from V<sup>3+</sup> solution so I think it may be vanadium(III) ferrocyanide, though I'd like to try making a larger amount of it.
[Edited on 8-10-2015 by zts16]woelen - 9-8-2015 at 21:54
I never tried vanadium(III) with ferrocyanides. Last week I ordered some V2O3 (still waiting for it) and with this I can make vanadium(III) salts
easily and then I'll try this myself. How stable is the red precipitate? Is it easily oxidized by air?Texium - 10-8-2015 at 06:51
I never tried vanadium(III) with ferrocyanides. Last week I ordered some V2O3 (still waiting for it) and with this I can make vanadium(III) salts
easily and then I'll try this myself. How stable is the red precipitate? Is it easily oxidized by air?
It is
stable under water, but I haven't tried drying it yet.
