I am wondering if there is any explanation for the dependence of solubility of Co(II) inorganic compounds in water on the counter ion. In particular, cobalt (II) cyanide is completely insoluble in water, unlike cobalt(II) bromide, chloride, nitrate, ... etc ?
Mr. Gabr,
Most probably there are data, but in the literature ftom 60s'-70s'.
I am not interested in solubility data of these compounds as I have them. I am more interested in a possible explanation for the effect of cyanide ion on Co(II) inorganic compounds that render water insoluble species unlike what is observed for Br-, Cl-, NO3-, ... etc
You may want to check the following discussions for its possible interest concerning to your query:
https://www.researchgate.net/post/How_to_remove_CoCl2_in_solution/1 https://www.researchgate.net/post/how_to_convert_cobalt_nitrate_to_cobalt_chloride
I think that the CN- ion has anti bonding Pi orbital that acts as Pi-acceptor ligand. As you know, the pi-acceptor ligands can coordinated to metal complex coalently. there for, the Co(II) complex with CN will be insoluble in water. in the other ions (Br- Cl-, ...) the complex has ionic properties.
Thanks Abolfazl. Are you aware of any examples in the literature that supports this point ?
Compounds with purely ionic character are usually more soluble in water than the ones with covalent character
Dear Moustafa, In 99% of complexes that containing CN, the CN ion dose not separate from the metal center. for example: the K3[Fe(CN)6] is soluble in water, but you can not find the K+, Fe3+,CN- in solution, because the K3[Fe(CN)6] in water is separated to K+ and [Fe(CN)6]3- .
Please note that K3[Fe(CN)6] is soluble in water (330 g /L) For details pl. see Wikipedia https://en.wikipedia.org/wiki/Potassium_ferricyanide
Regarding the cyanides of cobalt please note the foillwoing:
On reaction with cyanide Co(II) ions initially form the insoluble Co(CN)2 which dissolves in excess reagent to give a brown solution of hexacyanocobaltate(II) namely [Co(CN)6]-4 which is water soluble.
The relevant chemistry is available in all standard text books For example Vogel's Qualitative Inorganic Analysis
Co+2 + 2 CN- --> Co(CN)2 precipitate
Co(CN)2 + 4 CN- --> [Co(CN)6]4-
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