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+?

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

What splitting pattern would you predict for a tetrahedral complex?

Non-octahedral complexes

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

Chelate and Macrocyclic Effects

Chelating ligands

EDTA2,2'-bipyridine = bpy

acetylacetonate= acac

Chelate and Macrocyclic Effects

Macrocyclic ligands

Valinomycin 18-crown-6 Heme b