Cr(II) or Cr 2+ Consider the octahedral complex Cr[(en) 3 ] 2+ Octahedral complex with 4 d electrons. Octahedral complex with 4 d electrons

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1 Cr [Ar] 4s 1 3d 5 Cr 2+ [Ar] 3d 4 Consider the octahedral complex Cr[(en) 3 ] 2+ Cr(II) or Cr 2+ Pairing energy Octahedral complex with 4 d electrons Octahedral complex with 4 d electrons Δ is large 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 Which one? High Spin Crystal field splitting can result in high spin or low spin complexes, depending on the ligands 1

2 Crystal Field Splitting Energy d z 2 d x 2 -y 2 Δ Nature of the ligand determines Δ Strong Field Large Δ Ligands arranged in order of decreasing magnitude of the splitting of energies of d orbitals in coordination compounds d xy d xz d yz Weak Field Small Δ Strong Field Large Δ Strong-field ligands produce a Large Crystal Field Splitting, resulting in Low Spin complexes 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+ Strong Field Δ is Small 4 unpaired electrons en is a Strong Field ligand Weak Field 2

3 Strong-field ligands produce a large crystal field splitting, resulting in low spin complexes Distinction between high-spin and low-spin octahedral complexes can only be made for d 4 to d 7 Electron Configurations Cr(en) 3 2+ Low Spin d 0 -d 3 and d 8 -d 10 configurations have only one way of filling in e-. 2 unpaired electrons d 0 -d 3 configurations have only one way of filling in electrons d 3 Distinction between high-spin and low-spin octahedral complexes can only be made for d 4 to d 7 Electron Configurations d 7 High spin Δ < P Low spin Δ > P d 8 -d 10 configurations have only one way of filling in electrons How many unpaired electrons does [Re(H 2 O) 6 ]Cl 2 have? d 9 Is it a Low Spin or High Spin Complex? 3

4 Coordination Compounds Determine the Shape Determine Oxidation State of the metal Determine Number of of d electrons Determine if Ligand is Weak field or Strong field How many unpaired electrons does [Re(H 2 O) 6 ]Cl 2 have? [Re(H 2 O) 6 ]Cl 2 Octahedral Complex Draw energy level diagram How many unpaired electrons does [Re(H 2 O) 6 ]Cl 2 have? Re [Xe] 6s 2 5d 5 Re 2+ [Xe] 5d 5 [Re(H 2 O) 6 ] 2+ 2Cl - Oxidation State? Oxidation State = 2 (6 x 0) =2+ Re 2+ or Rhenium(II) How many unpaired electrons does [Re(H 2 O) 6 ]Cl 2 have? [Re(H 2 O) 6 ] 2+ 2Cl - d 5 E dz 2 dx 2 -y 2 dxy dxz dyz d-orbital splitting in an octahedral crystal field H 2 O is a weak field ligand 4

5 How many unpaired electrons does [Re(H 2 O) 6 ]Cl 2 have? [Re(H 2 O) 6 ] 2+ 2Cl - How many unpaired electrons does [Re(H 2 O) 6 ]Cl 2 have? [Re(H 2 O) 6 ] 2+ 2Cl - d 5 d z 2 d x 2 -y 2 Δ is small d 5 d z 2 d x 2 -y 2 5 unpaired e- dxy dxz dyz dxy dxz dyz High-spin complex MAGNETIC PROPERTIES Co [Ar] 4s 2 3d 7 Co 3+ [Ar] 3d 6 Why [CoF 6 ] -3 is paramagnetic and [Co(NH 3 ) 6 ] +3 is diamagnetic Octahedral Co 3+ d-orbital splitting in a Weak octahedral crystal field Δ is small Strong Field Weak Field F - is a Weak Field ligand 5

6 High-Spin complex Strong Field Paramagnetic NH 3 is a Strong Field ligand Weak Field High-Spin complex d-orbital splitting in a Strong octahedral crystal field High-Spin complex Low-Spin complex Δ is Large Paramagnetic Paramagnetic Diamagnetic The effects of ligands on the colors of coordination compounds The effects of ligands on the colors of coordination compounds [CoCl(NH 3 ) 5 ](NO 3 ) 2 [CoBr(NH 3 ) 5 ](NO 3 ) 2 6

7 The effects of ligands on the colors of coordination compounds The effects of ligands on the colors of coordination compounds [CoI(NH 3 ) 5 ](NO 3 ) 2 [CoNO 2 (NH 3 ) 5 ](NO 3 ) 2 The effects of ligands on the colors of coordination compounds The effects of ligands on the colors of coordination compounds [CoSO 4 (NH 3 ) 5 ]NO 3 [CoCO 3 (NH 3 ) 5 ]NO 3 Visible Spectrum (Each wavelength corresponds to a different color) Eye can detect photons from nm 400 nm Higher energy Lower energy Shorter Wavelength Longer Wavelength White = all the colors (wavelengths) 7

8 Cyan Magenta Yellow Cyan Magenta Yellow "White" light Cyan Yellow Yellow 8

9 Magenta Light Eye Compound Coordination compounds are highly colored because they can absorb photons in the visible region of the electromagnetic spectrum to produce the complementary color. 9

10 A solution of [CuCl 4 ] -2 is yellow. In what region of the electromagnetic spectrum does it absorb light? Yellow [CuCl 4 ] -2 A solution of [Cu(H 2 O) 4 ] +2 absorbs mostly at 580 nm. What should be its color? Yellow 10

11 [Cu(H 2 O) 4 ] +2 Coordination compounds are highly colored because they can absorb photons in the visible region of the electromagnetic spectrum to produce the complementary color. Explain the colors of: Cr [Ar] 4s 1 3d 5 Cr 3+ [Ar] 3d 3 [Cr(NH 3 ) 6 ]Cl 3 and [Cr(H 2 O) 6 ]Cl 3 Oxidation State: Cr 3+ [Cr(NH 3 ) 6 ]Cl 3 d z2 d x2-y2 Δ Large NH 3 is a stronger field ligand d xy d xz d yz 11

12 [Cr(NH 3 ) 6 ]Cl 3 absorbs at higher frequency (lower wavelength) i.e. in the blue. [Cr(NH 3 ) 6 ]Cl 3 absorbs at higher frequency (lower wavelength) i.e. in the blue. The complementary color is yellow [Cr(H 2 O) 6 ]Cl 3 d z2 d x2-y2 Δ Small H 2 O is a weaker field ligand d xy d xz d yz [Cr(H 2 O) 6 ]Cl 3 absorbs at lower frequency (higher wavelength) i.e. in the yellow. [Cr(H 2 O) 6 ]Cl 3 absorbs at lower frequency (higher wavelength) i.e. in the yellow. The complementary color is violet. 12