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Cr [Ar] 4s13d5 Cr2+ [Ar] 3d4 Consider the octahedral complex Cr[(en)3]2+ Cr(II) or Cr2+ Octahedral complex with 4 d electrons Octahedral complex with 4 d electrons Δ is large Pairing energy Δ is small Δ is large Typically, lower energy attained by pairing e- before populating higher E. Cr[(en)3]2+ Octahedral complex with 4 d electrons Low Spin High Spin Crystal field splitting can result in high spin or low spin complexes, depending on the ligands Which one? 1 Crystal Field Splitting Energy Spectrochemical Series dz2 dx2- y2 Strong Field Large Δ Δ Nature of the ligand determines Δ Ligands arranged in order of decreasing magnitude of the splitting of energies of d orbitals in coordination compounds dxy dxz dyz Weak Field Small Δ Strong-field ligands produce a Large Crystal Field Splitting, resulting in Low Spin complexes Spectrochemical Series Strong Field Large Δ Δ is Large Weak Field Small Δ 2 unpaired electrons Weak-field ligands produce a Small Crystal Field splitting, resulting in High Spin complexes Cr[(en)3]2+ Spectrochemical Series Strong Field Δ is Small Weak Field 4 unpaired electrons en is a Strong Field ligand 2 Strong-field ligands produce a large crystal field splitting, resulting in low spin complexes Cr(en)32+ Low Spin Distinction between high-spin and low-spin octahedral complexes can only be made for d4 to d7 Electron Configurations d0-d3 and d8-d10 configurations have only one way of filling in e-. 2 unpaired electrons d0-d3 configurations have only one way of filling in electrons Distinction between high-spin and low-spin octahedral complexes can only be made for d4 to d7 Electron Configurations d3 d7 High spin Δ<P d8-d10 configurations have only one way of filling in electrons Low spin Δ>P How many unpaired electrons does [Re(H2O)6]Cl2 have? d9 Is it a Low Spin or High Spin Complex? 3 Coordination Compounds How many unpaired electrons does [Re(H2O)6]Cl2 have? Determine the Shape Determine Oxidation State of the metal Determine Number of of d electrons [Re(H2O)6]Cl2 Determine if Ligand is Weak field or Strong field Octahedral Complex Draw energy level diagram Re [Xe] 6s25d5 Re2+ [Xe] 5d5 How many unpaired electrons does [Re(H2O)6]Cl2 have? [Re(H2O)6]2+ 2ClOxidation State? Oxidation State = 2 – (6 x 0) = 2+ Re2+ or Rhenium(II) How many unpaired electrons does [Re(H2O)6]Cl2 have? [Re(H2O)6]2+ 2ClE dz2 dx2-y2 dxy dxz dyz Spectrochemical Series d5 d-orbital splitting in an octahedral crystal field H2O is a weak field ligand 4 How many unpaired electrons does [Re(H2O)6]Cl2 have? How many unpaired electrons does [Re(H2O)6]Cl2 have? [Re(H2O)6]2+ 2Cl- [Re(H2O)6]2+ 2Cl- dz2 dx2-y2 d5 Δ is small dxy dxz dyz d5 dz2 dx2-y2 5 unpaired e- dxy dxz dyz Co [Ar] 4s23d7 High-spin complex Co3+ [Ar] 3d6 MAGNETIC PROPERTIES Why [CoF6]-3 is paramagnetic and [Co(NH3)6]+3 is diamagnetic Octahedral Co3+ d-orbital splitting in a Weak octahedral crystal field Spectrochemical Series Δ is small Strong Field Weak Field F- is a Weak Field ligand 5 High-Spin complex Spectrochemical Series Strong Field Weak Field NH3 is a Strong Field ligand Paramagnetic d-orbital splitting in a Strong octahedral crystal field Low-Spin complex High-Spin complex High-Spin complex Δ is Large Paramagnetic The effects of ligands on the colors of coordination compounds [CoCl(NH3)5](NO3)2 Paramagnetic Diamagnetic The effects of ligands on the colors of coordination compounds [CoBr(NH3)5](NO3)2 6 The effects of ligands on the colors of coordination compounds The effects of ligands on the colors of coordination compounds [CoI(NH3)5](NO3)2 [CoNO2(NH3)5](NO3)2 The effects of ligands on the colors of coordination compounds The effects of ligands on the colors of coordination compounds [CoSO4(NH3)5]NO3 [CoCO3(NH3)5]NO3 Visible Spectrum (Each wavelength corresponds to a different color) 400 nm Higher energy Shorter Wavelength 400 nm 500 nm 600 nm 700 nm Lower energy Longer Wavelength 700 nm Eye can detect photons from 400-700nm White = all the colors (wavelengths) 7 Blue Magenta Cyan Yellow Green Red Blue "White" light Magenta Cyan Yellow Green Red Blue Blue Cyan Red Yellow Yellow Green 8 Blue Blue Magenta Red Green Green Red Green Blue Blue Green Red Green Red Light Compound Coordination compounds are highly colored because they can absorb photons in the visible region of the electromagnetic spectrum to produce the complementary color. Eye 9 A solution of [CuCl4]-2 is yellow. In what region of the electromagnetic spectrum does it absorb light? Blue Yellow 500 nm 400 nm 600 nm 700 nm A solution of [Cu(H2O)4]+2 absorbs mostly at 580 nm. What should be its color? [CuCl4]-2 500 nm 400 nm Blue 600 nm 700 nm Blue Green Red Yellow Green Red 10 [Cu(H2O)4]+2 Explain the colors of: Coordination compounds are highly colored because they can absorb photons in the visible region of the electromagnetic spectrum to produce the complementary color. Cr [Ar] 4s13d5 Cr3+ [Ar] 3d3 [Cr(NH3)6]Cl3 and [Cr(H2O)6]Cl3 Oxidation State: Cr3+ [Cr(NH3)6]Cl3 Spectrochemical Series dz 2 dx2-y2 Δ Large NH3 is a stronger field ligand dxy dxz dyz 11 [Cr(NH3)6]Cl3 absorbs at higher frequency (lower wavelength) i.e. in the blue. 500 nm 400 nm 600 nm 700 nm [Cr(NH3)6]Cl3 absorbs at higher frequency (lower wavelength) i.e. in the blue. The complementary color is yellow 400 nm 500 nm 600 nm 700 nm [Cr(H2O)6]Cl3 Spectrochemical Series dz 2 dxy H2O is a weaker field ligand [Cr(H2O)6]Cl3 absorbs at lower frequency (higher wavelength) i.e. in the yellow. 400 nm 500 nm 600 nm 700 nm dx2-y2 dxz Δ Small dyz [Cr(H2O)6]Cl3 absorbs at lower frequency (higher wavelength) i.e. in the yellow. The complementary color is violet. 400 nm 500 nm 600 nm 700 nm 12
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