transition metal compounds have interesting magnetic ...courses.chem.psu.edu/chem112/summer/lecture...
TRANSCRIPT
Transition metal compounds have interesting magnetic properties.
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Diamagnetic Paramagnetic Ferromagnetic
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The magnetic properties of a complex depends on the number of unpaired electrons
Na+
Mn2+
Ti2+
Co3+
Experiment shows: [Co(CN)6]3– has no unpaired electrons [CoF6]3– has four unpaired electrons
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WHY do they have different numbers of unpaired electrons?
Presence of ligand electrons raises energy of metal d orbitals due to electrostatic repulsion
CRYSTAL FIELD THEORY can be used to explain this result.
M in spherical Oh Field
E
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d orbitals in free metal ion (all degenerate)"
d orbitals in uniform, “spherical” field of negative charge; all orbitals raised in
energy equally
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The octahedral ligand field (or crystal field) causes the d orbitals to split into two energy levels."
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e! config
# unpaired e!
P = spin pairing energy = energy needed to pair electrons in the same orbital.
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For an ion with a d4 electron configuration the number of unpaired electrons will depend on ".
Which one will be high spin (more unpaired e!)? Low spin (fewer unpaired e!)?
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The magnitude of " (=Crystal field splitting energy) influences the properties of metal complexes.
The magnitude of " depends on:
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How big is " ?
How does " affect properties of complexes?
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OCTAHEDRAL COMPLEXES"#92$."(5,9)%1"0'1*")@':5,G""
Which of the diagrams below corresponds to [CoF6]3– and which corresponds to [Co(CN)6]3–?
WHY?"
What properties of these complexes would be different?""
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Increasing"! "
Cl! < F! < H2O < NH3 < en < NO2! < CN!
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The color of a complex depends on: 1. The element 2. Its oxidation state 3. Identity of ligands
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Example: V(H2O)6
3+ green V(H2O)6
2+ violet
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When light of a certain wavelength is
absorbed by a complex, the complex
will appear the complementary color
of the wavelength absorbed (you see the light that is REFLECTED!)
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How do we explain the colors of metal complexes?
Visible absorption spectrum of [Ti(H2O)6]3+ : what color is it?
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Ni2+ (aq)
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[Ni(H2O)6]2+ + 6 NH3 h [Ni(NH3)6]3+ + 6 H2O
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The observed color is related to the amount of energy required to promote an electron.
Compare " to energy absorbed.
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Which of these complexes absorbs light at the shorter wavelength?
Which complex has the larger !o?"
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