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Topic: color; ligands vs regular anions  (Read 2368 times)

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Offline kiwitses

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color; ligands vs regular anions
« on: May 30, 2017, 06:42:35 PM »
hello there, i have a few questions, hope someone is kind enough to tell me how this goes, my native language is spanish, so excuse me for any mistakes i make beforehand

in the lab, i had a sample of copper to which i add concentrated nitric acid 70% w/m, forming copper (ii) nitrate

the solution had a greenish/blueish color, i assume this was due to water acting as a ligand distorting the d orbitals of copper, so if i were to obtain the anhydrous solid, it'd be colorless

now, it turns out the anhydrous solid has the same color as the solution

my question is, is the nitrate anion acting as a ligand here, distorting the orbitals of copper and causing a display of color, even though it doesn't bind itself to the copper through a dative bond like regular ligands do?

it seems that every time someone explains the color of ionic transition metals according to crystal field theory, the explanation involves ligands, as in ions or molecules that gave electron pairs to the d metal cation, rather than taking electrons from it in a redox reaction, so i'm at a loss here and kind of having a meltdown, wondering if i should treat regular transition metal salts as complexes when they're in aqueous solution


afterwards, i added concentrated sodium hydroxide to the copper (ii) nitrate solution and it went from greenish blue to deep sea blue, i assumed at first that the hydroxide substituted the water ligands, but seeing as regular ionic attraction might also be able to cause changes in color, i have no idea if i should treat the formed compound as an hydroxide copper complex or as a regular salt

Offline Enthalpy

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Re: color; ligands vs regular anions
« Reply #1 on: May 31, 2017, 05:05:50 AM »
¬°Bienvenido, kiwitses!

I have somehow in mind that if the colour is partly greenish, you obtained copper (I) mixed with copper (II) before adding NaOH. But I could be horribly wrong.

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