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IR and Electronic Spectra of transition metal complexes watch

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    Does anyone have any resources on the IR or electronic spectra of transition metal complexes? Searching on Google doesn't really reveal anything, and I need to do this for a lab.
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    What exactly are you looking for? Most have UV/vis spectra which allow you to probe the size of the crystal field splitting.

    As for the IR, typically the most interesting things are to look for changes in vibrational frequencies of ligands in the complex relative to the free ligand (e.g. CO stretching frequencies which become lower when they're involved in pi back-bonding).
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    (Original post by Kyle_S-C)
    What exactly are you looking for? Most have UV/vis spectra which allow you to probe the size of the crystal field splitting.

    As for the IR, typically the most interesting things are to look for changes in vibrational frequencies of ligands in the complex relative to the free ligand (e.g. CO stretching frequencies which become lower when they're involved in pi back-bonding).
    I'm having a hard time interpreting the IR and UV/Vis spectra of Bis(triphenylphosphine)nickel(II ) dichloride http://www.sigmaaldrich.com/catalog/ProductDetail.do?N4=237116|ALDRI CH&N5=SEARCH_CONCAT_PNO|BRAND_KE Y&F=SPEC .

    I'm told that the IR absorptions in a certain region are the NiCl bonds, but I can't see how people even derive that, and why there are 2 absorptions in it; shouldn't the 2 NiCl bonds be the same?

    Also, what does the absorbance and hence \epsilon from the beer law tell you? What is it supposed to mean.
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    (Original post by Lifeisnice)
    I'm having a hard time interpreting the IR and UV/Vis spectra of Bis(triphenylphosphine)nickel(II ) dichloride http://www.sigmaaldrich.com/catalog/ProductDetail.do?N4=237116|ALDRI CH&N5=SEARCH_CONCAT_PNO|BRAND_KE Y&F=SPEC .

    I'm told that the IR absorptions in a certain region are the NiCl bonds, but I can't see how people even derive that, and why there are 2 absorptions in it; shouldn't the 2 NiCl bonds be the same?

    Also, what does the absorbance and hence \epsilon from the beer law tell you? What is it supposed to mean.
    Water has two identical O-H bonds, yet it still has more than one vibrational mode...
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    (Original post by Lifeisnice)
    I'm having a hard time interpreting the IR and UV/Vis spectra of Bis(triphenylphosphine)nickel(II ) dichloride http://www.sigmaaldrich.com/catalog/ProductDetail.do?N4=237116|ALDRI CH&N5=SEARCH_CONCAT_PNO|BRAND_KE Y&F=SPEC .

    I'm told that the IR absorptions in a certain region are the NiCl bonds, but I can't see how people even derive that, and why there are 2 absorptions in it; shouldn't the 2 NiCl bonds be the same?

    Also, what does the absorbance and hence \epsilon from the beer law tell you? What is it supposed to mean.
    IR is to do with vibrational modes. Since you know the point group of the molecule(either sq planar which is D4h or tetrahedral which is Td), use the character table to work out total no of vibrational modes. That will tell you which one is IR active and which one is not(refer to character table; ie you need to know group theory before doing this, i presume)
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    (Original post by shengoc)
    IR is to do with vibrational modes. Since you know the point group of the molecule(either sq planar which is D4h or tetrahedral which is Td), use the character table to work out total no of vibrational modes. That will tell you which one is IR active and which one is not(refer to character table; ie you need to know group theory before doing this, i presume)
    Hmm... I haven't done group theory yet though; this is for a practical. What about the \epsilon value obtained at the maximum absorbance through the Beer law? Is it just a characteristic constant, or can it be used in some other way, other than classifying the peak.
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    (Original post by Lifeisnice)
    Hmm... I haven't done group theory yet though; this is for a practical. What about the \epsilon value obtained at the maximum absorbance through the Beer law? Is it just a characteristic constant, or can it be used in some other way, other than classifying the peak.
    I am not sure really, but uv spectra(electronic excitation) usually just indicates high amount of conjugation.
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    (Original post by shengoc)
    I am not sure really, but uv spectra(electronic excitation) usually just indicates high amount of conjugation.
    In organic chemistry, perhaps, but with metal complexes, you can actually gain a fair amount of useful data from it.

    The absorption coefficient (epsilon) is, thinking quantum mechanically, a measure of the allowedness of the transition in question - i.e.

    \epsilon\propto\langle a|\hat{\mu}|b\rangle

    with mu the dipole moment operator, and a and b the two states. Consequently, the intensity of a peak in the spectrum gives you some indication of the type of transition in question.
 
 
 
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