Chapter 24 Transition Metals and Coordination Compounds

1. Chemistry: A Molecular Approach, 1st Ed.Nivaldo Tro Chapter 24Transition Metals and Coordination Compounds Roy Kennedy Massachusetts Bay Community College Wellesley Hills, MA 2007, Prentice Hall

2. Gemstones • the colors of rubies and emeralds are both due to the presence of Cr3+ ions – the difference lies in the crystal hosting the ion Some Al3+ ions in Be3Al2(SiO3)6 are replaced by Cr3+ Some Al3+ ions in Al2O3 are replaced by Cr3+ Tro, Chemistry: A Molecular Approach

3. Properties and Electron Configuration of Transition Metals • the properties of the transition metals are similar to each other • and very different to the properties of the main group metals • high melting points, high densities, moderate to very hard, and very good electrical conductors • in general, the transition metals have two valence electrons – we are filling the d orbitals in the shell below the valence • Group 1B and some others have 1 valence electron due to “promotion” of an electron into the d sublevel to fill it • form ions by losing the ns electrons first, then the (n – 1)d Tro, Chemistry: A Molecular Approach

4. Atomic Size • the atomic radii of all the transition metals are very similar • small increase in size down a column Tro, Chemistry: A Molecular Approach

5. Ionization Energy • the first ionization energy of the transition metals slowly increases across a series • third transition series slightly higher 1st IE • trend opposite to main group elements Tro, Chemistry: A Molecular Approach

6. Electronegativity • the electronegativity of the transition metals slowly increases across a series • except for last element in the series • electronegativity slightly increases down the column • trend opposite to main group elements Tro, Chemistry: A Molecular Approach

7. Oxidation States • often exhibit multiple oxidation states • vary by 1 • highest oxidation state is group number for 3B to 7B Tro, Chemistry: A Molecular Approach

8. Coordination Compounds • when a complex ion combines with counterions to make a neutral compound it is called a coordination compound • the primary valence is the oxidation number of the metal • thesecondary valence is the number of ligands bonded to the metal • coordination number • coordination number range from 2 to 12, with the most common being 6 and 4 CoCl36H2O = [Co(H2O)6]Cl3 Tro, Chemistry: A Molecular Approach

9. Coordination Compound Tro, Chemistry: A Molecular Approach

10. Complex Ion Formation • complex ion formation is a type of Lewis acid-base reaction • a bond that forms when the pair of electrons is donated by one atom is called a coordinate covalent bond Tro, Chemistry: A Molecular Approach

11. Ligands with Extra Teeth • some ligands can form more than one coordinate covalent bond with the metal atom • lone pairs on different atoms that are separate enough so that both can reach the metal • chelate is a complex ion containing a multidentate ligand • ligand is called the chelating agent Tro, Chemistry: A Molecular Approach

12. Tro, Chemistry: A Molecular Approach

13. EDTAa Polydentate Ligand Tro, Chemistry: A Molecular Approach

14. Complex Ions with Polydentate Ligands Tro, Chemistry: A Molecular Approach

15. Geometries in Complex Ions Tro, Chemistry: A Molecular Approach

16. Common Ligands Tro, Chemistry: A Molecular Approach

17. phenanthroline Tro, Chemistry: A Molecular Approach

18. [Fe(en)(NH3)4]Cl3 • Fe is +3 • 3 moles of AgCl would form

19. Common Metals found in Anionic Complex Ions Tro, Chemistry: A Molecular Approach

20. Naming Coordination Compounds • List ligand names in alphabetical order • name each ligand alphabetically, adding a prefix in front of each ligand to indicate the number found in the complex ion • follow with the name of the metal cation, indicate the oxidation number with Roman numerals. • If the complex is an anion, the suffix “ate” is added to the metal name.

21. Ligands Names • anions ending with ate or ide change to “o” as in nitrate to nitrato or cyanide to cyano • anions with ite change to “e” • molecules uses common name except for: • water changes to aqua • ammonia to ammine • CO to carbonyl • multiple simple ligands are prefixed with di, tri, tetra, penta, or hexa. • Complex ligands are prefixed with bis, tris, tetrakis, pentakis, or hexakis.

22. Practice Tetracyanonicklate(II) potassium K2[Ni(CN)4] Na[Cr(C2O4)2(H2O)2] [Ru(phen)4]Cl3 Diaquobis(oxylato)chromate(III) sodium Tetrakis(phenanthroline)ruthunium(III) chloride

23. Practice aquachlorobis(ethylenediamine) cobalt(III) chloride Pentacarbonyliron(0) Triaminechloroetheylenediamenecobalt(III) [Co(H2O)(Cl)(en)2]2Cl Fe(CO)5 [Co(NH3)3(Cl)(en)]2+

24. Isomers • Structural isomers are molecules that have the same number and type of atoms, but they are attached in a different order • Stereoisomersare molecules that have the same number and type of atoms, and that are attached in the same order, but the atoms or groups of atoms point in a different spatial direction Tro, Chemistry: A Molecular Approach

26. Linkage Isomers Tro, Chemistry: A Molecular Approach

27. Geometric Isomers • geometric isomers are stereoisomers that differ in the spatial orientation of ligands • cis-trans isomerism in octahedral complexes MA4B2 • fac-mer isomerism in octahedral complexes MA3B3 • cis-trans isomerism in square-planar complexes MA2B2 Tro, Chemistry: A Molecular Approach

28. Ex. 24.5 – Draw the structures and label the type for all isomers of [Co(en)2Cl2]+ the ethylenediamine ligand (en = H2NCH2CH2NH2) is bidentate each Cl ligand is monodentate octahedral MA4B2 Tro, Chemistry: A Molecular Approach

29. Bonding in Coordination CompoundsValence Bond Theory • bonding takes place when the filled atomic orbital on the ligand overlaps an empty atomic orbital on the metal ion • explain geometries well, but doesn’t explain color or magnetic properties Tro, Chemistry: A Molecular Approach

30. Tro, Chemistry: A Molecular Approach

31. Bonding in Coordination CompoundsCrystal Field Theory • bonds form due to the attraction of the electrons on the ligand for the charge on the metal cation • electrons on the ligands repel electrons in the unhybridized d orbitals of the metal ion • the result is the energies of orbitals the d sublevel are split • the difference in energy depends on the complex and kinds of ligands • crystal field splitting energy • strong field splitting and weak field splitting Tro, Chemistry: A Molecular Approach

32. Splitting of d Orbital Energies due to Ligands in a Octahedral Complex Tro, Chemistry: A Molecular Approach

33. Strong and Weak Field Splitting Tro, Chemistry: A Molecular Approach

35. How we see color If we see black, the material absorbs all color If we see white, the material reflect all color Tro, Chemistry: A Molecular Approach

36. Complex Ion Color • Absorbs all colors-but- the one you see or • Reflects most colors but absorbs the the complimentary Tro, Chemistry: A Molecular Approach

37. Complex Ion Color and Crystal Field Strength • the colors of complex ions are due to electronic transitions between the split d sublevel orbitals • the wavelength of maximum absorbance can be used to determine the size of the energy gap between the split d sublevel orbitals Ephoton = hn = hc/l = D Tro, Chemistry: A Molecular Approach

38. Ligand and Crystal Field Strength • the strength of the crystal field depends in large part on the ligands • strong field ligands include: CN─ > NO2─ > en > NH3 • weak field ligands include: H2O > OH─ > F─ > Cl─ > Br─ > I─ • crystal field strength increases as the charge on the metal cation increases Tro, Chemistry: A Molecular Approach

39. Magnetic Properties andCrystal Field Strength • the electron configuration of the metal ion with split d orbitals depends on the strength of the crystal field • the 4th and 5th electrons will go into the higher energy dx2-y2 and dz2 if the field is weak and the energy gap is small – leading to unpaired electrons and a paramagnetic complex • the 4th thru 6th electrons will pair the electrons in the dxy, dyz and dxz if the field is strong and the energy gap is large – leading to paired electrons and a diamagnetic complex Tro, Chemistry: A Molecular Approach

40. diamagnetic paramagnetic low-spin complex high-spin complex Low Spin & High Spin Complexes only electron configurations d4, d5, d6, or d7 can have low or high spin Tro, Chemistry: A Molecular Approach

41. Tetrahedral Geometry andCrystal Field Splitting • because the ligand approach interacts more strongly with the planar orbitals in the tetrahedral geometry, their energies are raised • most high-spin complexes Tro, Chemistry: A Molecular Approach

42. Square Planar Geometry andCrystal Field Splitting • d8 metals • the most complex splitting pattern • most are low-spin complexes Tro, Chemistry: A Molecular Approach

43. Applications of Coordination Compounds • extraction of metals from ores • silver and gold as cyanide complexes • nickel as Ni(CO)4(g) • use of chelating agents in heavy metal poisoning • EDTA for Pb poisoning • chemical analysis • qualitative analysis for metal ions • blue = CoSCN+ • red = FeSCN2+ Tro, Chemistry: A Molecular Approach

44. chlorophyll Applications of Coordination Compounds • commercial coloring agents • prussian blue = mixture of hexacyanoFe(II) and Fe(III) • inks, blueprinting, cosmetics, paints • biomolecules • porphyrin ring • cytochrome C • hemoglobin • chlorphyll Tro, Chemistry: A Molecular Approach

45. Applications of Coordination Compounds • carbonic anhydrase • catalyzes the reaction between water and CO2 • contains tetrahedrally complexed Zn2+ Tro, Chemistry: A Molecular Approach

46. Applications of Coordination Compounds • Drugs and Therapeutic Agents • cisplatin • anticancer drug Tro, Chemistry: A Molecular Approach