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Chemistry 481(01) Spring 2014

Chemistry 481(01) Spring 2014. Instructor: Dr. Upali Siriwardane e-mail: upali@latech.edu Office: CTH 311 Phone 257-4941 Office Hours: M,W 8:00-9:00 & 11:00-12:00 am; Tu,Th , F 10:00 - 12:00 a.m . April 10 , 2014: Test 1 (Chapters 1,  2, 3,)

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Chemistry 481(01) Spring 2014

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  1. Chemistry 481(01) Spring 2014 • Instructor: Dr. Upali Siriwardane • e-mail: upali@latech.edu • Office: CTH 311 Phone 257-4941 • Office Hours: • M,W 8:00-9:00 & 11:00-12:00 am; • Tu,Th, F 10:00 - 12:00 a.m. • April 10 , 2014: Test 1 (Chapters 1,  2, 3,) • May 1, 2014: Test 2 (Chapters  5, 6 & 7) • May 20, 2014: Test 3 (Chapters. 19 & 20) • May 22, Make Up: Comprehensive covering all Chapters

  2. Chapter 7. An introduction to coordination compounds The language of coordination chemistry 7.1 Representative ligands 7.2 Nomenclature Constitution and geometry 7.3 Low coordination numbers 7.4 Intermediate coordination numbers 7.53Higher coordination numbers 7.6 Polymetallic complexes Isomerism and chirality 7.7 Square-planar complexes 7.8 Tetrahedral complexes 7.9 Trigonal-bipyrmidal and square-pyramidal complexes 7.10 Octahedral complexes 7.11 Ligand chirality

  3. Chapter 7. An introduction to coordination compounds Thermodynamics of complex formation 7.12 Formation constants 7.13 Trends in successive formation constants 7.14 Chelate and macrocyclic effects 7.15 Steric effects and electron delocalization

  4. Coordination compound A compound formed from a Lewis acid and Lewis base. Ametal or metal ion acting Lewis acid (being an electron pair acceptor) and a atom or group of atoms with lone electron pairs Lewis base electron pair donor forms an adduct with dative or coordinative covalent bonds. Ni(ClO4)2 (aq)+ 6NH3 → [Ni(NH3)6](ClO4)2 (aq) The Lewis bases attached to the metal ion in such compounds are called ligands.

  5. The coordination number (CN) CN of a metal ion in a complex is defined as the number of ligand donor atoms to which the metal is directly bonded. [Co(NH3)5Cl]2+ CN is 6, 1 chloride and 5 ammonia ligands each donating an electron pair. For organometallic compounds. An alternative definition of CN would be the number of electron pairs arising from the ligand donor atoms to which the metal is directly bonded.

  6. 1) What is a coordination compound?

  7. Coordination sphere • Coordination sphere - the sphere around the central ion made up of the ligands directly attached to it. Primary and secondary coordination sphere.

  8. Preparation of Complexes • The figure at left shows cyanide ions (in the form of KCN), being added to an aq. solution of FeSO4. • Since water is a Lewis base, the Fe2+ ions were originally in the complex [Fe(H2O)6]2+ • The CN- ions are driving out the H2O molecules in this substitution reaction that form the hexacyanoferrate(II) ion, [Fe(CN)6]4- . [Fe(H2O)6]2+ + 6 CN- [Fe(CN)6]4 + 6 H2O

  9. Various Colors of d-Metal Complexes The color of the complex depends on the identity of the ligands as well as of the metal.. Impressive changes of color often accompany substitution reactions.

  10. Structures and symmetries • Six-coordinate complexes are almost all octahedral (a). • Four-coordinate complexes can be tetrahedral (b) or square planar (c). • (Square planar usually occurs with d8 electron configurations, such as in Pt2+ and Au3+.)

  11. Representing Octahedral Shapes • Instead of a perspective drawing (a), we can represent octahedral complexes by a simplified drawing that emphasizes the geometry of the bonds (b).

  12. Ligands The Brønsted bases or Lewis base attached to the metal ion in such compounds are called ligands. These may be Simple ions such as Cl–, CN– Small molecules such as H2O or NH3, Larger molecules such as H2NCH2CH2NH2 N(CH2CH2NH2)3 Macromolecules, EDTA and biological molecules such as proteins.

  13. Representative Ligands and NomenclatureBidentate Ligands Polydentate Ligands • Some ligands can simultaneously occupy more than one binding site. • Ethylenediamine (above) has a nitrogen lone pair at each end, making it bidentate. It is widely used and abbreviated “en”, as in [Co(en)3]3+.

  14. Ethylenediaminetetraacetate Ion(EDTA) • EDTA4- is another example of a chelating agent. It is hexadentate. • This ligand forms complexes with many metal ions, including Pb2+, and is used to treat lead poisoning. • Unfortunately, it also removes Ca2+ and Fe2+ along with the lead. • Chelating agents are common in nature.

  15. Porphyrins and phthalocyanins

  16. Chelates • The metal ion in [Co(en)3]3+ lies at the center of the three ligands as though pinched by three molecular claws. It is an example of a chelate, • A complex containing one or more ligands that form a ring of atoms that includes the central metal atom.

  17. Naming Transition Metal Complexes • Cation name first then anion name. • List first the ligands, then the central atom • The ligand names are made to end in -O if negative • Anion part of the complex ends in -ate Eg. Cu(CN)64- is called the hexacyanocuprate(II) ion • The ligands are named in alphabetic order • Number of each kind of ligand by Greek prefix • The oxidation state of the central metal atom shown in parenthesis after metal name • Briding is shown with  ( -oxo)

  18. Some Common Ligand Names

  19. Names of Ligands (continued)

  20. Coordination Sphere Nomenclature • Cationic coordination sphere • -ium ending Anionic coordination sphere • -ate ending

  21. Examples • [Co(NH3)4Cl2]Cl: • dichlorotetramminecobalt(III) chloride • [Pt(NH3)3Cl]2[PtCl4]: di(monochlorotriammineplatinum(II)) tetrachloroplatinate(II). • K3[Fe(ox)(ONO)4] : • potassium tetranitritooxalatoferrate(III)

  22. Use bis and tris for di and trifor chelating ligands • [Co(en)3](NO3)2 : • tris(ethylenediamine)cobalt(II) nitrate • [Ir(H2O)2(en)2]Cl3 • bis(ethylenediamine)diaquairidium(III) chloride • [Ni(en)3]3[MnO4] : • Tris(ethylenediamine)nickel(II) tetraoxomanganate(II)

  23. Naming • [Cu(NH3)4]SO4 tetraaminecopper(II) sulfate • [Ti(H2O)6][CoCl6] hexaaquatitanium(III) • hexachlorocobaltate(III) K3[Fe(CN)6] • potassium hexacyanoferrate(III)

  24. 2) Give the formula of following coordination compounds a)Dichlorobis(ethylenediammine)nickle b) Potasiumtrichloro(ethylene)platinate(1-)

  25. c) Tetrakis(pyridine)platinum(2+) tetrachloroplatinate(2-) d) Tetraamminebis(ethylenediamine) --hydroxo--amidodicobalt(4+) chloride

  26. 3) Give the names of following coordination compounds a)       [Co(NH3)6]Cl3; b)       trans-[Cr(NH3)4(NO2)2]+ ; c)       K[Cu(CN)2] ; d)       cis-[PtCl2(NH3)2] ; e)       fac-[Co(NO2)3(NH3)3]Cl3

  27. The Eta(h) System of Nomenclature • For forp bonded ligands number of atoms attached to the metal atom is shown by hn (h5-cyclopentadienyl) tricarbonyl manganese tetracarbonyl (h3-allyl) manganese, Mn(C3H5)(CO)4

  28. Isomers • Both structural and stereoisomers are found. • The two ions shown below differ only in the positions of the Cl- ligand, but they are distinct species, with different physical and chemical properties.

  29. 4)       What is the geometry and coordination number of compounds in the problem above? a)       [Co(NH3)6]Cl3; b)       trans-[Cr(NH3)4(NO2)2]+ ; c)       K[Cu(CN)2] ; d)       cis-[PtCl2(NH3)2] ; e)       fac-[Co(NO2)3(NH3)3]Cl3

  30. 5)  Draw the formula and find the BITE of following ligands. a)       2,2'-bipyridine (bipy) ; b)       terpy; c)       cyclam; d)       edta;

  31. Ionization Isomers • These differ by the exchange of a ligand with an anion (or neutral molecule) outside the coordination sphere. [CoSO4(NH3)5]Br has the Br- as an accompanying anion (not a ligand) and [CoBr(NH3)5]SO4 has Br - as a ligand and SO42-as accompanying anion.

  32. IonizationIsomers The red-violet solution of [Co(NH3)5Br]SO4 (left) has no rxn w/ Ag+ ions, but forms a ppt. when Ba2+ ions are added. The dark red solution of [CoSO4(NH3)5]Br (right) forms a ppt. w/ Ag+ ions, but does not react w/ Ba2+ ions.

  33. Hydrate Isomers • These differ by an ex-change between an H2O molecule and another ligand in the coordination sphere. • The solid, CrCl3. 6H2O, may be any of three compounds. • [Cr(H2O)6]Cl3 (violet) • CrCl(H2O)5]Cl2.H2O (blue-green) • CrCl2 (H2O)4Cl.2H2O (green) • Primary and secondary coordination spheres

  34. Linkage Isomers The triatomic ligand is the isothiocyanato, NCS-. In (b) it is the thiocyanato, SCN-. Other ligands capable or forming linkage isomers are NO2- vs. ONO - CN - vs. NC - . (a) NSC- ligand (the N is closest to the center); (b) SCN- ligand (S is closest the center)

  35. Coordination Isomers • These occur when one or more ligands are exchanged between a cationic complex and an anionic complex. • An example is the pair [Cr(NH3)6][Fe(CN)6] and[Fe(NH3)6][Cr(CN)6].

  36. Stereoisomers • Ionization, hydrate, linkage, and coordination isomers are all structural isomers. • In stereoisomers, the formulas are the same. The atoms have the same partners in the coordination sphere, but the arrangement of the ligands in space differs. • The cis- and trans- geometric isomers shown in next slide differ only in the way the ligands are arranged in space. • There can be geometric isomers for octahedral and square planar complexes, but not for tetrahedral complexes.

  37. Square Planar ComplexesGeometric Isomers • Properties of geometric isomers can vary greatly. • The cis- isomer below is pale orange-yellow, has a solubility of 0.252 g/100 g water, and is used for chemotherapy treatment. • The trans- isomer is dark yellow, has a solu-bility of 0.037 g/100 g water, and shows no hemotherapeutic effect.

  38. 6)  Describe the geometrical isomerism in following compounds: a)       [Co(NH3)4Cl2]+ ; b)       [IrCl3(PPh3)3] ; c)       [Cr(en)2Cl2] ;

  39. cis and trans-PtCl2(NH3)2

  40. Trans Effect & Influence

  41. Preparation Geometrical Isomers

  42. Optical Isomerism The two complexes at left are mirror images. (The gray rectangle represents a mirror, through which we see somewhat darkly.) No matter how the complexes are rotated, neither can be superimposed on the other. Note only four of the six ligands are different.

  43. Combined Stereoisomerisms • Both geometrical and optical isomerism can occur in the same complex, as below. The trans- isomer is green. • The two cis- isomers, which are optical isomers of each other, are violet.

  44. Identifying Optical Isomerism If a molecule or ion belong to a point group with a Sn axis is not optically active

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