1. University Chemistry Chapter 15: The Chemistry of Transition Metals Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. What are the transition metals ? Element with typical electron configurations ns 2 (n-1)d x incompletely filled d orbitals Properties “metallic” due to loosely bound ns electrons. Various colors Various reduction/oxidation potentials Possess catalytic activities

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5. 17.1 The d-block Metals: Energies, Charge States and Ioinc Radii Charge states (oxidation states) Early transition metalsLate transition metals Early d elements: Formation of oxyions by polar-covalent bonding with O, Cl, F Metal ions (mostly coordination complex ions) ** * High oxidation states do not mean the ionic charges of the metals. Just oxidation numbers! Late d elements: resistant to further oxidation beyond M 2+ or M 3+

6. 6 Ionization Energies for the 1 st Row Transition Metals

7. 17.1 The d-block Metals: Energies, Charge States and Ioinc Radii Ionic radii Similar to neutral ones. Not a so smooth change as for the p elements.

8. 17.2 chemistry of the early transition metals: oxyions Oxyions : metals combined with oxygen to form a polyatomic molecular ion. dichromate Oxidizing agents examples Cr 2 O 7 2- MnO 4 - permanganate CrO 4 2- + H 2 O Cr 2 O 7 2- H 2 SO 4 CrO 3 H2OH2O H 2 CrO 4 Sc 2 O 3 TiO 2 V2O5V2O5 Oxidation states: higher oxidation state– more covalent bond character lower oxidation state – more ionic bond character Mn(OH) 2, Mn(OH) 3, H 2 MnO 3, H 2 MnO 4, HMnO 4 basic acidic

9. 17.2 chemistry of the early transition metals: oxyions Spectroscopy and structure of oxyanions Comparison of isoelectronic species MnO 4 - CrO 4 2- VO 4 3- Absorption spectra Follows octet rule. Tetrahedral structure according to VSEPR. *

10. 17.2 chemistry of the early transition metals: oxyions MnO 4 - CrO 4 2- VO 4 3- follow octet rule, Tetrahedral structure Molecular orbitals 4p and 4s AO are spatially more extended than 3d, to interact with oxygen MO’s. 3d AO’s remain as nonbonding.

11. 17.2 chemistry of the early transition metals: oxyions MnO 4 - CrO 4 2- VO 4 3- follow octet rule, Tetrahedral structure Molecular orbitals Charge-transfer transitions : electron jumps from O to M like orbitals. This can absorb light very strongly.

12. 17.3 chemistry of the late transition metals: coordination complexes Stoichiometry, Isomerism, and Geometry of Complexes CoCl 3. 6NH 3 CoCl 3. 5NH 3 CoCl 3. 4NH 3 CoCl 3. 3NH 3 Chemical formula(19thC.)Color orange-yellow purple green [Co(NH 3 ) 6 ] 3+ Cl - 3 Chemical formula (Werner) [Co(NH 3 ) 5 Cl] 2+ Cl - 2 [Co(NH 3 ) 4 Cl 2 ] + Cl - [Co(NH 3 ) 3 Cl 3 ] Octahedral structure 1 Isomers 1 2 1 cis trans These two are geometrical isomers

13. 17.3 chemistry of the late transition metals: coordination complexes Fe 2+ (aq) Color of aqueous solution of ions CuSO 4 : greenish white Coordination complex : Cu(H 2 O) 4 2+ CuSO 4.4H 2 O : blue v.s. Fe 3+ (aq) Co 2+ (aq) Co 3+ (aq)Ni 2+ (aq)Cu 2+ (aq) coordination Ligand coordination complex m : coordination number Making coordination complex charge of a complex = sum of charges of metals and ligands charge of a complex + charges of counter ions = 0 coordination number = numbers of donor atoms Oxidation numbers of 2 and 3 (1 is possible for Cu). Formation of common oxides: Fe 3 O 4, Fe 2 O 3, CoO, Co 3 O 4, NiO, Cu 2 O, CuO, ZnO Oxides are easily soluble in acid to form colored solution. d 10 (Cu, Zn) are colorless. These colors are due to the formation of coordination complexes.

14. 14 Coordination Compounds A coordination compound typically consists of a complex ion and a counter ion. A complex ion contains a central metal cation bonded to one or more molecules or ions. The molecules or ions that surround the metal in a complex ion are called ligands. A ligand has at least one unshared pair of valence electrons H O H H N H H Cl - C O Primary valence corresponds to the oxidation number and secondary valence to the coordination number of the element.

15. 15 The atom in a ligand that is bound directly to the metal atom is the donor atom. H O H H N H H The number of donor atoms surrounding the central metal atom in a complex ion is the coordination number. Ligands with: one donor atom monodentate two donor atoms bidentate three or more donor atoms polydentate H 2 O, NH 3, Cl - ethylenediamine EDTA

16. 16 H 2 N CH 2 CH 2 NH 2 bidentate ligand polydentate ligand (EDTA) Bidentate and polydentate ligands are called chelating agents

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18. 18 EDTA Complex of Lead Net charge of a complex ion is the sum of the charges on the central metal atom and its surrounding ligands. Pb 2+ EDTA 4- Complex: 2-

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20. 17.3 chemistry of the late transition metals: coordination complexes Nomenclature 1. Cation Anion b 2. In the complex: names of ligands come first and then name of metal. Among ligands: alphabetical order. 3. Names of ligands: anion – change the last letter to o. neutral – same as the original ones. 4. Counting number of ligands: di, tri, tetra, penta, hexa, hepta….. if the ligand contains these names in it, use: bis, tris, tetrakis, pentakis…… 5. If the compex is an anion: at the end of the name put ate. 6. Oxidation number of metal: in parenthesis with Roman letter - (IV). Examples Pentaamminechlorocobalt(III) chloridePotassium hexacyanoferrate(II) [Co(NH 3 ) 5 Cl]Cl 2 K 4 [Fe(CN) 6 ]

21. 21 Naming Coordination Compounds The cation is named before the anion. Within a complex ion, the ligands are named first in alphabetical order and the metal atom is named last. The names of anionic ligands end with the letter o. Neutral ligands are usually called by the name of the molecule. The exceptions are H 2 O (aquo), CO (carbonyl), and NH 3 (ammine). When several ligands of a particular kind are present, the Greek prefixes di-, tri-, tetra-, penta-, and hexa- are used to indicate the number. If the ligand contains a Greek prefix, use the prefixes bis, tris, and tetrakis to indicate the number. The oxidation number of the metal is written in Roman numerals following the name of the metal. If the complex is an anion, its name ends in –ate.

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26. 26 Structure of Coordination Compounds Coordination numberStructure 2 4 6 Linear Tetrahedral or Square planar Octahedral

27. Structure of coordination complexes Linear[Ag(NH 3 ) 2 ] + [Zn(NH 3 ) 4 ] 2+ Atomic orbital of metal coordination number 2 structure Tetrahedral 4 [Pt(NH 3 ) 4 ] 2+ Square Planar 4 [Co(NH 3 ) 6 ] 3+ Octahedral 6 d 10 d8d8 d6d6 17.3 chemistry of the late transition metals: coordination complexes * (b) and (c) are geometrical isomers.

28. 28 Stereoisomers are compounds that are made up of the same types and numbers of atoms bonded together in the same sequence but with different spatial arrangements. Geometric isomers are stereoisomers that cannot be interconverted without breaking a chemical bond. cis-[Pt(NH 3 ) 2 Cl 2 ] trans-[Pt(NH 3 ) 2 Cl 2 ]

29. 29 cis-[Co(NH 3 ) 4 Cl 2 ] trans-[Co(NH 3 ) 4 Cl 2 ] cis trans same compounds Rotate 90 o

30. 30 Optical isomers are nonsuperimposable mirror images. cis-[Co(en) 2 Cl 2 ]trans-[Co(en) 2 Cl 2 ] optical isomers chiral not optical isomers achiral Rotate 180 o

31. 17.3 chemistry of the late transition metals: coordination complexes Multidentate ligands (or chelating ligands) bidentate ligands tetradentate These are non-superimposable mirror images to each other. So they are optical isomers. hexadentate

32. 32 The porphine molecule plays an important role in some biological compounds. Coordination Compounds in Living Systems hemoglobin chlorophyll Cytochrome c

33. 17.3 chemistry of the late transition metals: coordination complexes Magnetism: paramagetic v.s. diamagnetic (paramagnetic if there are unpaired electrons) [Co(NH 3 ) 6 ] 3+ diamagnetic – no unpaired electrons [CoF 6 ] 3- paramagnetic – 4 unpaired electrons Zn 2+ always diamagnetic – no unpaired electronsd 10 d6d6 d6d6 low spin complex high spin complex Lability: Some ligands bind to metals more tightly than others, replacing weakly bound ligands. Replacement of a strong ligand by a weak one is labile. CO, CN -, H 2 NCH 2 CH 2 NH 2 > H 2 O K f is called the formation constant of a complex (see Table 17.3). ability to undergo a reaction (should meet both the kinetic and thermodynamic requirements).

34. 17.4 The spectrochemical series and bonding in complex Color changes of complexes more stable Spectrochemical Series: Arrangement of ligands in order of increasing stability of complex. Magnetic properties also follow this series. weak field ligands strong field ligands a high-spin complex a low-spin complex Example: Fe(CN) 6 4- Example: Fe(H 2 O) 6 2+ paramageticdiamagnetic Strong-field ligands form a high-spin complex that are paramagnetic, whereas weak-field ligands form a paramagnetic low-spin complex.

36. 17.4 The spectrochemical series and bonding in complex Are there ways to explain and eventually predict colors, spectrochemical series and magnetism? Crystal field theory : ionic description of the metal-ligand bonds Only considering the electrostatic interaction between ligand and metal atom: charge-charge, charge-dipole. Then, consider changes in the energy levels of metal d orbitals according to the interaction during coordination. Let’s Begin with octahedral geometry

37. 37 Bonding in Coordination Compounds All d orbitals equal in energy in the absence of ligands! Crystal field theory explains the bonding in complex ions purely in terms of electrostatic forces. the attraction between the positive metal ion and the negatively charged ligand or the partially negatively charged end of a polar ligand electrostatic repulsion between the lone pairs on the ligands and the electrons in the d orbitals of the metals

38. 38 Isolated transition metal atom Splitting in Octahedral Complexes Bonded transition metal atom Crystal field splitting (  ) is the energy difference between two sets of d orbitals in a metal atom when ligands are present The lobes of the and are pointed directly at the ligands, increasing their energy.

39. Crystal field theory for the octahedral structure  o : crystal field splitting energy Overall stabilization through splitting : crystal field stabilization energy (CFSE)

40. 40 Color of Coordination Compounds Absorbs all wavelengths: Black Transmits all wavelengths: Colorless (white) If one color is absorbed, the complementary color is seen. A solution of CuSO 4 absorbs orange wavelengths so the solution appears blue. Energy of absorbed photon = 

41. 41 Different values of , result in different colors exhibited by complex ions. Aquo complexes of first row transition metal ions. Ti 3+ Co 2+ Cr 3+ Mn 2+ Fe 3+ Cu 2+ Ni 2+ Complexes will be colorless if no light is absorbed or if the absorbed wavelength is not in the visible region.

42. 42 Spectroscopic Determination of  =498 nm

43. 43 I - < Br - < Cl - < OH - < F - < H 2 O < NH 3 < en < CN - < CO Spectrochemical Series Strong-field ligands Large  Weak-field ligands Small  A list of ligands arranged in increasing order of their abilities to split the d-orbital energy levels. increasing 

44. 44 Magnetic Properties weak-field ligandstrong-field ligand Actual number of unpaired electrons can be determined by electron spin spectroscopy ( ESR). The arrangement of the electrons is determined by the stability gained by having maximum parallel spins versus the investment in energy required to promote electrons to higher d orbitals.

45. 45 Orbital diagrams for the high- spin and low-spin octahedral complexes corresponding to the electron configurations d 4, d 5, d 6, and d 7. No such distinctions can be made for d 1, d 2, d 3, d 8, d 9, and d 10.

46. Summary of Octahedral Complexes magnetism d 1 ~ d 5 : always paramagnetic d 7 ~ d 9 : always paramagnetic d 10 : always diamagnetic d 6 : depending on the ligands

47. Tetrahedral Complexes ??? Reversal of octahedral !!!

48. Tetrahedral complexes Reversal of octahedral !

49. 49 Splitting in Tetrahedral Complexes The d xy, d yz, and d xz orbitals are more closely directed at the ligands

50. Square planar??? Removal of axial ligands from octahedral

52. 52 Splitting in Square Planar Complexes The orbital possesses the highest energy and the d xy orbital the next highest. However, the relative placement of the and the d xz and d yz orbitals must be calculated.

54. 54 Ligand Field Theory Molecular orbital approach to the electronic structure of coordination compounds. Based on the idea that atomic orbitals that are close in energy will mix more effectively in molecular orbitals than those that are far apart. The remaining d orbitals—d xy, d yz and d xz —are oriented in between the ligands and will remain nonbonding orbitals and orbitals on the metal center will mix with the ligand lone-pair orbitals to form two bonding and two antibonding molecular orbitals. Weak point of crystal field theory 1. Coordination is not fully ionic. 2. Spectrochemical series is all empirical. Ligand field theory 3. Does not consider nature of the ligands.

55. 55 Provides an understanding of the dependence of the crystal field splitting on the ligand type. Arrangement of the highest occupied molecular orbitals (3d xy, 3d yz, 3d xz, and the two  * d orbitals) is identical to that predicted by crystal field theory

56. I - < Br - < Cl - < F -, OH - < H 2 O < NCS - < NH 3 < en < CO, CN - Now, we can explain Spectrochemical Series Weak field Ligands Strong field Ligands small  o large  o Interaction between d xy of metal and p y of halide: charge repulsion Increases energy level of t 2g Makes smaller  o for I - and less smaller one for F -  back-bonding  back-bonding of ligand can overlap  with d xy orbital Lowers the energy level of t 2g Makes larger  o for CO, CN -

57. 57 Ligand exchange (or substitution) reactions kinetic lability - tendency to react labile complex—undergo rapid ligand exchange reactions. inert complex—a complex ion that undergoes very slow exchange reactions A thermodynamically unstable species is not necessarily chemically reactive. A thermodynamically stable species (that is, one that has a large formation constant) is not necessarily unreactive. instantaneous *CN: 14 C labeled several days

58. 58 Applications of Coordination Compounds Metallurgy extract and purify metals, Therapeutic Chelating Agents EDTA is used in the treatment of lead poisoning. Certain platinum-containing compounds can effectively inhibit the growth of cancerous cells.

59. 59 Chemical Analysis Detergents Tripolyphosphate ion is an effective chelating agent that forms stable, soluble complexes with Ca 2+ ions. Characteristic colors are used in qualitative analysis to identify nickel and palladium. dimethylglyoxime bis(dimethylglyoximato)nickel(II)

60. 60 Cisplatin – The Anticancer Drug Cisplatin works by chelating DNA (deoxyribonucleic acid), the molecule that contains the genetic code. Consequently, the double-stranded structure assumes a bent configuration at the binding site which is thought to inhibit replication.