Crystal Field Theory

1. Crystal Field Theory • Focus: energies of the d orbitals • Assumptions • 1. Ligands: negative point charges • 2. Metal-ligand bonding: entirely ionic • strong-field (low-spin): large splitting of d orbitals • weak-field (high-spin): small splitting of d orbitals

4. dxy dxz dyz dz2 dx2- y2 isolated metal ion _ _ _ _ _ d-orbitals d-orbital energy level diagram for tetrahedral _ _ _  _ _ E only high spin

5. isolated metal ion _ _ _ _ _ d-orbitals d-orbital energy level diagram square planar __ dx2- y2 __ dxy __ dz2 E __ __ dxz dyz only low spin

6. Crystal-Field Theory square planar Examples: Pd2+, Pt2+, Ir+, and Au3+.

7. Tetrahedral Complexes

10. High spin Low spin

12. Spectrochemical Series: An order of ligand field strength based on experiment: Weak Field • I- Br- S2- SCN- Cl- NO3- F-  C2O42- H2O NCS- CH3CN NH3 en  bipy phen NO2- PPh3 CN- CO Strong Field

13. Colors of Transition Metal Complexes • Compounds/complexes that have color: • absorb specific wavelengths of visible light (400 –700 nm) • wavelengths not absorbed are transmitted and appear as color

14. Color and Magnetism Color Color of a complex depends on; (i) the metal, (ii) its oxidation state & (iii) ligands (i.e., everything) For example, pale blue [Cu(H2O)6]2+ versus dark blue [Cu(NH3)6]2+. Partially filled d orbitals usually give rise to colored complexes because they can absorb light from the visible region of the spectrum.

15. Color and Magnetism Color

16. Visible Spectrum wavelength, nm (Each wavelength corresponds to a different color) 400 nm 700 nm higher energy lower energy White = all the colors (wavelengths)

18. Complexes and Color The larger the gap, the shorter the wavelength of light absorbed by electrons jumping from a lower-energy orbital to a higher one.

20. [Ti(H2O)6]3+ Absorbs in green yellow. Looks purple.

21. the spectrum for [Ti(H2O)6]3+ has a maximum absorption at 510 nm Absorbs green & yellow, transmits all other wavelengths, the complex is purple.

22. Crystal-Field Theory [Ti(H2O)6]3+

23. Electronic Configurations of Transition Metal Complexes • d orbital occupancy depends on  and pairing energy, P • e-’s assume the electron configuration with the lowest possible energy cost • If  > P ( large; strong field ligand) • e-’s pair up in lower energy d subshell first • If  < P ( small; weak field ligand) • e-’s spread out among all d orbitals before any pair up

24. d-orbital energy level diagramsoctahedral complex d1

25. d-orbital energy level diagramsoctahedral complex d2

26. d-orbital energy level diagramsoctahedral complex d3

27. d-orbital energy level diagramsoctahedral complex d4 low spin  > P high spin  < P

28. d-orbital energy level diagramsoctahedral complex d5 low spin  > P high spin  < P

29. d-orbital energy level diagramsoctahedral complex d6 low spin  > P high spin  < P

30. d-orbital energy level diagramsoctahedral complex d7 low spin  > P high spin  < P

31. d-orbital energy level diagramsoctahedral complex d8

32. d-orbital energy level diagramsoctahedral complex d9

33. d-orbital energy level diagramsoctahedral complex d10

35. Different composition! Coordination complexes: isomers Isomers: same atomic composition, different structures We’ll check out the following types of isomers: Hydrate Linkage Cis-trans Optical (Enantiomers)

36. Hydrate isomers: Water in outer sphere (water that is part of solvent) Water in the inner sphere water (water is a ligand in the coordination sphere of the metal)

37. Structural Isomerism 1 • Coordination isomerism: • Composition of the complex ion varies. • [Cr(NH3)5SO4]Br • and [Cr(NH3)5Br]SO4

38. Coordination-Sphere Isomers • Example [Co(NH3)5Cl]Br vs. [Co(NH3)5Br]Cl • Consider ionization in water [Co(NH3)5Cl]Br [Co(NH3)5Cl]+ + Br- [Co(NH3)5Br]Cl[Co(NH3)5Br]+ + Cl-

39. Structural Isomerism 2 • Ligand isomerism: • Same complex ion structure but point of attachment of at least one of the ligands differs. • [Co(NH3)4(NO2)Cl]Cl • and [Co(NH3)4(ONO)Cl]Cl

40. Linkage Isomers

41. Example: Linkage isomers Bonding to metal may occur at the S or the N atom Bonding occurs from N atom to metal Bonding occurs from S atom to metal

42. Linkage Isomers [Co(NH3)5(NO2)]Cl2 Pentaamminenitrocobalt(III) chloride [Co(NH3)5(ONO)]Cl2 Pentaamminenitritocobalt(III) chloride

43. Stereoisomers • Stereoisomers • Isomers that have the same bonds, but different spatial arrangements • Geometric isomers • Differ in the spatial arrangements of the ligands

44. Stereoisomerism 1 • Geometric isomerism (cis-trans): • Atoms or groups arranged differently spatially relative to metal ion • Pt(NH3)2Cl2

47. Geometric Isomers cis isomer trans isomer Pt(NH3)2Cl2

48. Geometric Isomers cis isomer trans isomer [Co(H2O)4Cl2]+

49. Cl- Cl- Stereoisomers: geometric isomers (cis and trans)

50. Stereoisomers • Optical isomers • isomers that are nonsuperimposable mirror images • said to be “chiral” (handed) • referred to as enantiomers • A substance is “chiral” if it does not have a “plane of symmetry”