[JoshP]

Hey guys,

I'm at university, and in one of our lab sessions the other day we were preparing a thiocyanato-nickel complex. At the start, this involving dissolving the nickel nitrate hexahydrate in ethanol, as well as adding ethanol to an aqueous solution of KSCN. I was wondering, does this mean that molecules of ethanol would be surrounding the nickel/SCN-, rather than water? Seems like the answer woud obviously be 'yes', but I thought I'd check. Is this significant, if so? Why ethanol, as opposed to water? All I can think of is it being something to do with product solubilities, but H2O and ethanol are both polar protic solvents, so it doesn't seem like this would be the case...hope all this is clear. Thanks for an *delete me*

Josh 

[SirRoderick]

As the number of CH2 groups in ROH increases (H₂O still fits in there), the dielectric constant decreases. If you think of these molecules as containing a polar component (OH) and a non-polar component (R), then the polarity of a compound reflects the balance between these two components. As the relative amount of hydrocarbon character increases, the polarity decreases.

So presumably you need to have a lower diëlectric constant to succesfully solvate your complex. It's not a black-white thing (polar/apolar).

EXAMPLE
While KOH is very soluble in water, 1-bromobutane is not. Conversely, while 1-bromobutane will dissolve in hexane, KOH is completely insoluble. What's needed is a solvent that has just the right balance of polar and non-polar character. In fact, both methanol and ethanol are suitable choices.

[AWK]

Many different nickel complexes you can obtain  depending on the stoichiometry of reagents and solvent added. So this procedure allow you to isolate one of these possible complexes. You should know from your texbook - which one. My guess is K₂[Ni(SCN)₄]