lect20_ch24e_3pg

lect20_ch24e_3pg - Spectrochemical Series Low and High Spin...

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Unformatted text preview: Spectrochemical Series Low and High Spin Complexes Charge Transfer in d0 Oxyanions Chemistry 123 Spring 2008 Dr. Woodward eg eg Δ Δ t2g t2g Spectrochemical Series I- < Br- < Cl– < F- < H2O < NH3 < en < NO2- < CN- < CO Small Δ Large Δ Weak Field Ligand Weak M-L interaction Strong Field Ligand Strong M-L interaction 1 Which is [Cr(H2O)6]3+ and which is [CrF6]3- ? F is lower than H2O in the spectrochemical series. This decreases the energy splitting of the d-orbitals and shifts the absorption maximum to longer wavelengths. Which is [Cu(H2O)4]2+ and which is Cu[NH3]42+ ? 2.0 1.8 1.6 absorbance 1.4 2+ [Cu(H2O)4] 1.2 2+ [Cu(NH3)4] 1.0 0.8 0.6 0.4 0.2 0.0 200 300 400 500 600 700 800 900 wavelength (nm) NH3 is higher than H2O in the spectrochemical series. This increases the energy splitting of the d-orbitals and shifts the absorption maximum to shorter wavelengths. 2 Tetrahedral vs. Octahedral Coordination dxy dyz dxz Energy dz2 dx2-y2 x2- Δtetr Δoct dxy dyz dxz dz2 dx2-y2 x2- Spherical crystal field dz2 dx2-y2 x2- Tetrahedral crystal field dxy dyz dxz Octahedral crystal field Δtetrahedron ≈ (4/9) Δoctahedron Consequently tetrahedral complexes are always high spin. High spin & low spin states Small Δ Large Δ Δ < spin pairing energy Δ > spin pairing energy High Spin Configuration Low Spin Configuration Electrons are placed one in each orbital until we get to 6 electrons when we must start pairing electrons The t2g set of dorbitals are filled completely before any electrons are placed in the higher energy eg set of orbitals Paramagnetic Diamagnetic (unpaired electrons) (no unpaired electrons) Note: Low spin complexes are not always diamagnetic 3 Spin State Flow Chart Coordination Geometry Tetrahedron Square Planar Octahedron High Spin Low Spin 1st (3d), 2nd (4d) or 3rd (5d) row transition metal 1st Row Depends on Ligand & Metal F-, Cl-, Br-, I- = High Spin CN-, CO = Low Spin 2nd or 3rd Row Low Spin 4 ...
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