1. CHEM1612 - Pharmacy Week 8: Complexes II Dr. Siegbert Schmid School of Chemistry, Rm 223 Phone: 9351 4196 E-mail: siegbert.schmid@sydney.edu.au

2. Unless otherwise stated, all images in this file have been reproduced from: Blackman, Bottle, Schmid, Mocerino and Wille, Chemistry, John Wiley & Sons Australia, Ltd. 2008 ISBN: 9 78047081 0866

3. Lecture 22-3 Complexes Blackman, Bottle, Schmid, Mocerino & Wille Chapters 13,10.4, 11.8 Complex ions Coordination compounds Geometry of complexes Chelates K stab Solubility and complexes Nomenclature Isomerism in complexes Biologically important metal-complexes Co(EDTA) -

4. Lecture 22-4 Rules for nomenclature of coordination compounds: Name cation, then anion, as separate words. Examples: [Pt(NH 3 ) 4 Cl 2 ](NO 2 ) 2 tetraamminedichloridoplatinum(IV) nitrite [Pt(NH 3 ) 4 (NO 2 ) 2 ]Cl 2 tetraamminedinitritoplatinum(IV) chloride Name the ligands then the metal, all in same word. Number of ligands as Greek prefixes (di-, tri-, tetra-, penta-, hexa-), except ligands that already have numerical prefixes which use Latin prefixes (bis, tris, tetrakis…)  e.g. bis(ethylenediamine) for (en) 2 Nomenclature I

5. Lecture 22-5 Nomenclature II Oxidation state in Roman numeral in parentheses after name of metal  e.g. [Ag(NH 3 ) 2 ]NO 3 diamminesilver(I) nitrate Anionic ligands end in '-ido‘: Neutral ligands named as molecule, except those listed here: (Please modify accordingly pp.518-519 of your book) Ligand NameFormula FluoridoF - ChloridoCl - BromidoBr - IodidoI - CyanidoCN - HydroxidoOH - Ligand NameFormula AmmineNH 3 AquaH 2 O CarbonylCO NitrosylNO

6. Lecture 22-6 Ligands named in alphabetical order (but prefixes do not affect the order)  e.g. [Co(NH 3 ) 5 Cl]SO 4 pentaamminechloridocobalt(III) sulfate Anionic complexes end in ‘-ate’  e.g. K 3 [CrCl 6 ] potassium hexachloridochromate(III) Some metals in anionic complexes use Latin -ate names: Nomenclature of Ligands Not Ironate Not Copperate Not Leadate Not Silverate Not Goldate Not Tinnate

7. Lecture 22-7 Nomenclature - Exercises [Co(H 2 O) 6 ]CO 3 hexaaquacobalt(II) carbonate [Cu(NH 3 ) 4 ]SO 4 tetraamminecopper(II) sulfate (NH 4 ) 3 [FeF 6 ] ammonium hexafluoridoferrate(III) K 4 [Mn(CN) 6 ] potassium hexacyanidomanganate(II)

8. Lecture 22-8 Example 1: Find O.N. of Co in : [Co(NH 3 ) 5 Cl]SO 4 pentaamminechloridocobalt(?) sulfate [Co(NH 3 ) 5 Cl] 2+ ammine is neutral, chloride is -1 O.N. -1 = +2 (sum of O.N.s = overall charge) O.N. = +3 Assigning oxidation numbers Example 2: Find O.N. of Mn in :K 4 [Mn(CN) 6 ] potassium hexacyanidomanganate(?) [Mn(CN) 6 ] 4- (CN) is -1 overall O.N. + 6x(-1) = -4 (sum of O.N.s = overall charge) ON = +2

9. Lecture 22-9 Isomerism in Complexes Complexes can have several types of isomers: Structural Isomers: different atom connectivities 1. Coordination sphere isomerism 2. Linkage isomerism Stereoisomers: same atom connectivities but different arrangement of atoms in space 3. Geometric isomerism 4. Optical isomerism

10. Lecture 22-10 Coordination Isomers Ligands and counter-ions exchange place: Example: [Pt(NH 3 ) 4 Cl 2 ](NO 2 ) 2 tetraamminedichloridoplatinum(IV) nitrite [Pt(NH 3 ) 4 (NO 2 ) 2 ]Cl 2 tetraamminedinitritoplatinum(IV) chloride Two sets of ligands are reversed: [Cr(NH 3 ) 6 ][Co(CN) 6 ]NH 3 is a ligand for Cr 3+ [Co(NH 3 ) 6 ][Cr(CN) 6 ]NH 3 is a ligand for Co 3+ ligands counterions

11. Lecture 22-11 Linkage isomers Occur when a ligand has two alternative donor atoms. thiocyanate ion cyanate ion cyanato NCO:→ isocyanato OCN:→ thiocyanato NCS:→ isothiocyanato SCN:→ Pentaammineisothiocyanatocobalt(III)pentaamminethiocyanatocobalt (III)

12. Lecture 22-12 Square planar complex. Four coordinate: cis- and trans-[Pt(NH 3 ) 2 Cl 2 ] Stereoisomers: Geometric Isomers No anti-tumour effect cisplatin – highly effective anti-tumour agent Figure from Silberberg, “Chemistry”, McGraw Hill, 2006.

13. Lecture 22-13 Stereoisomers: Geometric Isomers 2 Cl next to each other Octahedral complex. Six coordinate: cis- and trans- [Co(NH 3 ) 4 Cl 2 ] + violet green 2 Cl axial to each other

14. Lecture 22-14 [NiClBrFI] 2- Stereoisomers: Optical Isomers When a molecule is non-superimposable with its mirror image. Example: four different substituents about tetrahedral centre. Same physical properties, except direction in which they rotate the plane of polarized light.

15. Lecture 22-15 cis-[Co(NH 3 ) 4 Cl 2 ] + cis-[Co(en) 2 Cl 2 ] + + + Has no optical isomers Has optical isomers Stereoisomers: Optical isomers Metal atoms with tetrahedral or octahedral geometries (but not square planar) may be chiral due to having different ligands. For the octahedral case, several cases are possible, e.g. 1. Complex with four ligands of two types.

16. Lecture 22-16 [M(en) 3 ] n+ complexes have optical isomers: Not superimposable 3+ Mirror plane Stereoisomers: Optical isomers 2. Having three bidentate ligands of only one type - gives a propeller-type structure. www.pt-boat.com

17. Lecture 22-17 Octahedral complex - stereoisomerism rotation of I by 180° gives III ≠ II Mirror image Cis- Dichlorido Bis(ethylendiamine)cobalt(III) ion Figure from Silberberg, “Chemistry”, McGraw Hill, 2006.

18. Lecture 22-18 Octahedral complex - stereoisomerism rotation of I by 270° gives III = II Mirror image Trans- Dichlorido Bis(ethylendiamine)cobalt(III) ion Figure from Silberberg, “Chemistry”, McGraw Hill, 2006.

19. Lecture 22-19 Biologically Important Complexes Many biomolecules contain metal ions that act as Lewis acids. Give some examples of naturally occurring complexes. Heme Chlorophyll Vitamin B12 Enzyme Carbonic anhydrase

20. Lecture 22-20 Heme Heme is a square planar complex of Fe 2+ and the tetradentate ring ligand porphyrin (bonds to 4 donor N atoms). Present in hemoglobin, which carries oxygen in blood, and myoglobin, which stores oxygen in muscle. Porphyrin ring O 2 bound to Fe 2+ Myoglobin protein Blackman Figure 13.37

21. Lecture 22-21 Chlorophyll Chlorophyll is a photosynthetic pigment, that gives leaves the characteristic green colour. It is a complex of Mg 2+ and a porphyrin ring system (four N atoms are the chelae). Figure from Silberberg, “Chemistry”, McGraw Hill, 2006.

22. Lecture 22-22 Dorothy Crowfoot Hodgkin The Nobel Prize in Chemistry 1964 Nobelprize.org Vitamin B 12 Image download from Wikipedia

23. Lecture 22-23 CO 2(g) + 2H 2 O (l) H 3 O + (aq) + HCO 3 - (aq) Carbonic anhydrase Tetrahedral complex of Zn 2+. Catalyses reaction between water and carbon dioxide during respiration. Coordinated to 3 N, fourth site left free to interact with molecule whose reaction is being catalysed (here with water). By withdrawing electron density, makes water acidic to lose proton and OH - attacks partial positive C of CO 2 much more vigorously. Cd 2+ is toxic because it competes with zinc for this spot. Figure downloaded from Wikipedia

24. Lecture 22-24 Summary Concepts:  Complex formation  Stability constant and stepwise stability constant  Acidity of some metal ions in solution  Coordination compounds and geometry  Nomenclature of coordination compounds  Isomerism in Complexes Calculations  Complex Formation  Equilibria in solution: complex formation + solubility

25. Lecture 22-25 Question Does the square planar complex ion [Pt(NH 3 )(N 3 )BrCl] - have optical isomers? Br Pt N=N=N NH 3 Cl Br Pt NH 3 Cl N=N=N This complex has no optical isomers because it can be superimposed on its mirror image.

26. Lecture 22-26 Coordination Compound Complex Ion Counter Ions Coordination compounds Figure from Silberberg, “Chemistry”, McGraw Hill, 2006.

27. Lecture 22-27 Metal complex formation can influence the solubility of a compound. e.g. AgCl (s) + 2 NH 3 [Ag(NH 3 ) 2 ] + + Cl - This occurs in 2 stages: AgCl (s) Ag + + Cl - (1) Ag + + 2 NH 3 [Ag(NH 3 ) 2 ] + (2) Complex formation removes the free Ag + from solution and so drives the dissolution of AgCl forward. Complex Formation and solubility

28. Lecture 22-28 AgBr (s) Ag + (aq) + Br - (aq) K overall = K sp x K stab = = 5.0·10 -13 x 1.7·10 7 = 8.5·10 -6 1.0 M NH 3 Ag + (aq) + 2NH 3(aq) [Ag(NH 3 ) 2 ] + (aq) AgBr (s) + 2NH 3(aq) [AgNH 3 ] + (aq) + Br - (aq) (1) (2) (1)+(2) Solubility of AgBr in Ammonia [Ag(NH 3 ) 2 + ][Br - ] [NH 3 ] Initial Conc. Change Equilibrium Conc. 1.0 M -2x 1.0 - 2x 0 +x x 0 +x x Substitute: K overall = x 2 /(1.0-2x) 2 = 8.5·10 -6 x = 2.9·10 -3 M Solubility of AgBr in NH 3 is 2.9·10 -3 M (c.f. in thiosulfate 0.45 M) K stab (Ag(NH 3 ) 2 + )= 1.7·10 7 )

29. Lecture 22-29 NO 2 - nitro O 2 N:→ nitrito ONO:→ Linkage Isomers NN O O O O [Co(NH 3 ) 5 (NO 2 )]Cl 2 Pentaamminenitrocobalt(III) chloride [Co(NH 3 ) 5 (ONO)]Cl 2 Pentaamminenitritocobalt(III) chloride Figure from Silberberg, “Chemistry”, McGraw Hill, 2006.