Chemistry 223 Chapter 24 Coordination Complexes

1. Chemistry 223 Chapter 24 Coordination Complexes

2. d-block elements a.k.a. transition metals • d-block elements are: • all metals • all have partially filled d subshells • exhibit horizontal & vertical similarities • alloys & compounds are important components • of materials in modern world • most first-row transition metals are essential • for life

3. General Trends among Transition Metals

4. 4th row Horizontal Periodic Trends

5. General Trends among Transition Metals Going across row from left toright, e-’s are added to 3d subshell to neutralize increase in (+) charge of nucleus as atomic # increases.

6. General Trends among Transition Metals • 3dsubshellfill based on • aufbau principle & Hund’s rule • with two important exceptions: • Crhas • Cuis • Anomalies due to

7. Reactivity: Sizeof neutral atoms of d-block elements gradually decreases left torightacross a row. Due to increase in Zeffwith increasing atomic # Atomic radius increases going down a column.

8. lanthanide contraction: ionic radii is ______________________ of lanthanide elements due to ______________________ of nuclear charge by 4f e-’s. increase in size btwn 3d & 4d metals is much > increase than btwn 4d & 5d metals

10. Reactivity: Zeffexperienced by valence e-’s in d-elements does not D as nuclear charge increases across a row Ionization energies of these elements increase very slowly going across a given row

11. Going from top left to bottom right corner of d block: • electronegativities increase • Densities increase • Electrical & thermal conductivities increase • Enthalpies of hydration of metal cations decrease

12. Transition metals become less reactive (more “Noble”) going from left to right across a row Relatively high ionization E & Electronegativities & relatively low Enthalpies of Hydration

13. Trends in Transition Metal Oxidation States: • All first-row transition metals (except Sc) • form stable compounds w/ 2+ ion. • Small difference btwn 2nd & 3rd ionization energies • all (except Zn) also form stable compounds w/ 3+ ion

15. Trends in Transition Metal Oxidation States: • Electronegativities of first-row transition metals • increase smoothly from Sc to Cu • Exceptions to overall trends attributable to stability associated with filled and half-filled subshells • e.g. Sc Ti V Cr Mn Fe Co Ni Cu Zn 1.36 1.54 1.63 1.66 1.55 1.83 1.88 1.91 1.901.65

16. Trends in Transition Metal Oxidation States: Transition metals form cations by initial loss of ns e-’s, even though ns orbital is lower in energy than (n–1)d subshell in the neutral atom.

17. Trends in Transition Metal Oxidation States: Small E difference btwn ns and (n-1)d plus screening effect means loss of 1 e- & (n-1)d orbital becomes lower in E. All transition-metal cations possess dnvalence e- configurations for 2+ ions of first-row.

18. Trends in Transition Metal Oxidation States: maxoxid states for 2nd & 3rd row transition metals in Groups 3 thru 8 increase from +3 for Y and La to +8 for Ru and Os

19. Trends in Transition Metal Oxidation States: Going farther to right, maximum oxidation state decreases, reaching +2 for elements of Group 12, which corresponds to

20. Trends in Transition Metal Oxidation States: Acid-base character of transition-metal oxides depend strongly on:

21. Trends in Transition Metal Oxidation States: • Oxides of metals in lower oxidation states • have ionic character and tend to be _______. • Oxides of metals in higher oxidation states • are more covalent and tend to be _________, • dissolving in strong base to form

22. A Brief Survey of Transition Metal Chemistry

23. Compounds of Mn in +2 to +7 oxidation states Different # of d electrons = different colors

24. Cobalt Blue

25. Coordination Compounds Metallic elements act as Lewis acids form complexes with various Lewis bases. Metal complex:

26. Coordination Compounds Central metal atom (or ion) bonded to one or more ligands. Ligands:

27. Coordination Compounds Complex ions:

28. Coordination Compounds Coordination compounds & complexes are distinct chemical species

29. History of Coordination Compounds Coordination compounds used since ancient times, but chem nature unclear. Werner: modern theory of coordination chemistry - based on studies of several series of

30. History of Coordination Compounds Werner postulated that metal ions have two different kinds of valence: primary valence(oxidation state) = secondary valence(coordination #) =

31. Measured Cl- amounts by adding Ag+ to make a ppt Alfred Werner (1866-1919)

32. Same chemical composition, same # of groups of same types attached to same metal. What made the two different colors?

33. Structures of Metal Complexes Coordination #’s of metal ions in metal complexes can range from _______________ Differences in Ebtwn different arrangements of ligands greatest for complexes w/ _______ coordination #’s & decrease as coordination #

34. Structures of Metal Complexes Only one or two structures possible for complexes w/ low coordination #’s. Several different energetically = structures are possible for complexes with high coordination #’s

36. Structures of Metal Complexes Coordination # 2 Rare for most metals; common for d10 metal ions, especially:

37. Structures of Metal Complexes Coordination # 3 Encountered with d10 metal ions e.g. Based on VSEPR: 3-coordinate complexes have

38. Coordination # 4 Two common structures: tetrahedral & sqplanar ______________: all 4-coordinate complexes of non-transition metals & d10ions and first-row transition metals, especially those with halide ligands.

39. Coordination # 4 Two common structures: tetrahedral & square planar _____________________: 4-coordinate complexes of 2nd & 3rd row transition metals with d8e- configurations, e.g. also encountered in some _____________ complexes

40. Structures of Metal Complexes Coordination # 5 Less common than 4 & 6. Found in two different structures: trigonal bipyramidal and square pyramidal. Many 5-coordinate complexes have distorted structures.

41. Structures of Metal Complexes Coordination # 6 Most common: six ligands at vertices of an _________________or a distorted octahedron. only other 6-coordinate structure is _______________________ uncommon in simple metal complexes.

43. Structures of Metal Complexes Coordination # 7 Uncommon usually only ____________ (e.g. 2nd & 3rd row transition metals, lanthanides, & actinides)

44. Structures of Metal Complexes Coordination # 7 3 different structures: two derived from an octahedron or a trigonal prism by adding a ligand to one face of polyhedron to give a “capped” octahedron or trigonal prism. Most common is

45. Structures of Metal Complexes Coordination # 8 Common for larger metal ions Simplest structure is the cube, rare because it does not minimize inter-ligand repulsive interactions. Common structures are square antiprism & dodecahedron, both of which can be generated from the cube.

46. Structures of Metal Complexes Coordination # 9 Found for larger metal ions Most common structure is tricappedtrigonal prism

48. Stability of Metal Complexes Thermodynamic stability of metal complex depends on:

49. Stability of Metal Complexes Metal-ligand interaction is an example of Lewis acid-base interaction. Lewis acid accepts pair of e-’s Lewis base donates lone pair of e-’s Lewis bases (Must have ________________ to donate)

50. Stability of Metal Complexes • Lewis bases (Must have lone pair e- to donate) • two categories: • Hard bases: • contain small, highly electronegative, relatively non-polarizable donor atoms