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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?
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+?
When octahedra are distorted, the resulting geometries changethe energies of the eg and t2g orbitals (break degeneracy)
Non-octahedral complexes
Octahedron Elongated octahedron
Square pyramid
Square plane
d8 (and d9) are special electron counts for square planar complexes
Non-octahedral complexes
ΔO
dx2-y2
dz2
dxy
dxz dyz
Which metals (with which ligands) will form square planar complexes?
Square planar complexes are important in homogeneous catalysis
Non-octahedral complexes
Catalytic hydrogenation of olefins using
Wilkinson's catalyst
Tetrahedral complexes
Co[CoCl4] + 12 H2O ---> 2 Co(H2O)6Cl2
(deep blue, tetrahedral CoCl42-) (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??
Metal-en complexation
[Co(H2O)6]2+ + 6 NH3 [Co(NH⇌ 3)6]2+ + 6 H2O
[Co(H2O)6]2+ + 3 en [Co(en)⇌ 3]2+ + 6 H2O