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 tot he 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. Naming Coordination Compounds • determine the name of the noncomplex ion • determine the ligand names and list them in alphabetical order • determine the name of the metal cation • name the complex ion by: • 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 • write the name of the cation followed by the name of the anion Tro, Chemistry: A Molecular Approach

17. Common Ligands Tro, Chemistry: A Molecular Approach

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

19. 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

21. Linkage Isomers Tro, Chemistry: A Molecular Approach

22. 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

23. 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

24. [Co(en)3]3+ Optical Isomers • optical isomers are stereoisomers that are nonsuperimposable mirror images of each other Tro, Chemistry: A Molecular Approach

25. Ex 24.7 – Determine if the cis-trans isomers of [Co(en)2Cl2]+ are optically active • draw the mirror image of the given isomer and check to see if they are superimposable cis isomer mirror image is nonsuperimposable trans isomer identical to its mirror image no optical isomerism optical isomers Tro, Chemistry: A Molecular Approach

26. Bonding in Coordination CompoundsValence Bond Theory • bonding take 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

27. Tro, Chemistry: A Molecular Approach

28. 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 the complex and kinds of ligands • crystal field splitting energy • strong field splitting and weak field splitting Tro, Chemistry: A Molecular Approach

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

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

31. Complex Ion Color • the observed color is the complimentary color of the one that is absorbed Tro, Chemistry: A Molecular Approach

32. 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

33. 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

34. 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

35. 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

36. 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

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

38. 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

39. 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

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

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