Chapter 5 - Coordination chemistry

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Crystal stabilization energy (CFSE)
CFSE = Energy lowering in the "crystal field" of the ligands,
e.g., in an octahedral or tetrahedral complex
Compare the CFSE for [Cr(CN)6]4- and [Cr(H2O)6]2+
What are the rules for high spin vs. low spin?
Crystal stabilization energy (CFSE)
Hydration enthalpies of M2+ ions
Can you explain the trends?
Magnetic Susceptibility
Molecules and ions that contain unpaired electrons are paramagnetic
We can count the number of spins by measuring the susceptibility
magnetic moment: µ ≈ µspin = [n(n+2)]1/2µBohr
What µs values would you expect for Ni2+ and Cu2+?
Non-octahedral complexes
When octahedra are distorted, the resulting geometries change
the energies of the eg and t2g orbitals (break degeneracy)
Octahedron
Elongated
octahedron
Square
pyramid
Square
plane
Non-octahedral complexes
d8 (and d9) are special electron counts for square planar complexes
dx2-y2
ΔO
dxy
dz2
dxz
dyz
Which metals (with which ligands) will form square planar complexes?
Non-octahedral complexes
Square planar complexes are important in homogeneous catalysis
Catalytic hydrogenation of
olefins using
Wilkinson's catalyst
Non-octahedral complexes
What splitting pattern would you predict for a tetrahedral complex?
Tetrahedral complexes
Co[CoCl4] + 12 H2O
(deep blue, tetrahedral CoCl42-)
--->
2 Co(H2O)6Cl2
(light pink, octahedral [Co(H2O)6]2+)
Why are tetrahedral complexes
more strongly colored than
octahedral ones?
Jahn-Teller Effect
Complexes with unequal populations of electrons in upper (antibonding)
orbitals distort to lower their energy
[Cu(OH2)6]2+
[Cu(OH2)5]2+
Chelate and Macrocyclic Effects
Multidentate ("chelating") ligands make very stable complexes
What is different about these reactions??
[Co(H2O)6]2+ + 6 NH3 ⇌ [Co(NH3)6]2+ + 6 H2O
[Co(H2O)6]2+ + 3 en ⇌ [Co(en)3]2+ + 6 H2O
Metal-en
complexation
Chelate and Macrocyclic Effects
Chelating ligands
EDTA
2,2'-bipyridine = bpy
acetylacetonate
= acac
Chelate and Macrocyclic Effects
Macrocyclic ligands
Valinomycin
18-crown-6
Heme b

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