savetheprawns
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I know that the ion Cu2+ is blue/green...

But why is [CuCl4]2- yellow?

Have i got it wrong in thinking that it's Cu is +2 in this?

Thanks,

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phen
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I have never speculated on anything close to this before, but I'm guessing this is because the Cl atoms affect the electrons on the Cu atom in a sort of 'covalent' way (i.e. not just electrostatic bonding), which causes the thing to become yellow, because the electrons around the Cu atom will interact differently with photons (I'm guessing this is in solution).

Seriously though, don't go by my speculation.

(Original post by EierVonSatan)
.
Maybe this helps. :P

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charco
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(Original post by savetheprawns)
I know that the ion Cu2+ is blue/green...

But why is [CuCl4]2- yellow?

Have i got it wrong in thinking that it's Cu is +2 in this?

Thanks,

x
This is crystal field theory.

It's yellow because the chloride ligands 'split' the 'd' orbitals so as to produce two sets of non-degenerate orbitals that differ in energy by the same energy as the colour removed from white light to leave yellow.

The complex is tetrahedral and splits the 'd' orbitals to give two with lower energy (slightly different) and three with higher. The 'd' electrons can make transitions between these orbitals by absorbing wavelengths (energy) from light.
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Aaron Harding00
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[Cu(Cl)4] 2- is a complex ion, your right in saying the copper ion is 2 . The chlorine bonded are what's known as ligands (chlorines have shared a pair of electrons to the copper through it's empty d-orbitals) which change the energy required for copper to hold it's own electrons in it's particular d-orbitals (splitting of the d-orbitals). That basically means the copper ion complex and the bonded electrons in it absorb different frequencies of light to the typical copper 2 ion so of the white light shined on the complex ion, the mix of colours left over mix to make the yellow It does rather than the blue your used to seeing
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charco
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(Original post by Aaron Harding00)
[Cu(Cl)4] 2- is a complex ion, your right in saying the copper ion is 2 . The chlorine bonded are what's known as ligands (chlorines have shared a pair of electrons to the copper through it's empty d-orbitals) which change the energy required for copper to hold it's own electrons in it's particular d-orbitals (splitting of the d-orbitals). That basically means the copper ion complex and the bonded electrons in it absorb different frequencies of light to the typical copper 2 ion so of the white light shined on the complex ion, the mix of colours left over mix to make the yellow It does rather than the blue your used to seeing
... more than 9 years ago :eek:

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Victor Volkov
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TDDFT: ub3lyp: 6-31 g(d,p) and LANL2DZ CuCl4transition wavelength absorption contribution 8 524.0245 0.0008 ligand10 472.8792 0.0197 ligandCu(NH3)42 606.27967 0.0001 d-d3 604.38819 0.0001 d-d
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