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Chapter 22 Transition Elements

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  1. Chapter 22Transition Elements Valdosta State University

  2. Transition Elements – d- and f-block • Used in construction and manufacturing (iron), coins (nickel, copper, zinc), ornamental (gold, silver, platinum). • Densest elements (osmium d=22.49 g/cm3, iridium d=22.41g/cm3). • Highest melting point (tungsten, mp=3410oC) and lowest melting point (mercury, mp=-38.9oC).

  3. Metal Chemistry • Radioactive elements with atomic number less than 83 (technetium 43; promethium 61). • All elements are solids, but mercury. • Have metallic sheen, conduct electricity and heat. • Are oxidized and form ionic compounds. • Some are essential to living organisms: Cobalt (vitamin B12), iron (hemoglobin and myoglobin), molybdenium and iron (nitrogenase). • Compounds are highly colored and used as pigments: Fe4[Fe(CN)6)3 14 H2O (prussian blue), TiO2 (white). • Ions give color to gemstons: Iron(II) ions give yellow color in citrine and chromium(III) ions produce the red color of a ruby. Valdosta State University

  4. Electron Configurations • General: • [noble gas core] nsa (n-1) db • Valance electrons for transition elements reside in the ns and (n-1) d subshells.

  5. Reactions • All metals undergo oxidation with oxygen, halogens, aqueous acids. • First the outermost electron is removed, followed by one or more d electrons. • Some generate cations with unpaired electrons = paramagnetism. • Are colored. • For first transition series common oxidation numbers are +2 and +3. Fe: [Ar]3d64s2 Fe2O3 Fe3+ [Ar]3d5 Fe + O2 Fe + Cl2 Fe + HCl FeCl3 Fe3+ [Ar]3d5 Fe + Cl2 FeCl2 + H2 Fe2+ [Ar]3d6 Fe + HCl Fe + O2

  6. Most common Trends: Oxidation number Valdosta State University

  7. Trends: Atom Radius Valdosta State University

  8. Trends: Density Valdosta State University

  9. Trends: Melting Point

  10. Metallurgy: Element Sources Valdosta State University

  11. Pyrometallurgy • Involves high temperature, such as Fe • C and CO used as reducing agents in a blast furnace • Fe2O3 + 3 C ---> 2 Fe + 3 CO • Fe2O3 + 3 CO ---> 2 Fe + 3 CO2 • Lime added to remove impurities, chiefly SiO2 SiO2 + CaO ---> CaSiO3 • Product is impure cast iron or pig iron Valdosta State University

  12. Hydrometallurgy • Use aqueous solutions (flotation). Some use bacteria. • Add CuCl2(aq) to ore such as CuFeS2 (chalcopyrite)CuFeS2(s) + 3 CuCl2(aq) --> 4 CuCl(s) + FeCl2(aq) + 2 S(s) • Dissolve CuCl with xs NaClCuCl(s) + Cl-(aq) --> [CuCl2]- • Cu(I) disproportionates to Cu metal2 [CuCl2]- --> Cu(s) + CuCl2 (aq) + 2 Cl- Native copper Azurite, 2CuCO3•Cu(OH)2 Valdosta State University

  13. •• H H N H •• H O H •• Coordination Compounds • combination of two or more atoms, ions, or molecules where a bond is formed by sharing a pair of electrons originally associated with only one of the compounds. Valdosta State University

  14. Coordination Chemistry Pt(NH3)2Cl2 “Cisplatin” - a cancer chemotherapy agent Co(H2O)62+ Cu(NH3)42+

  15. Coordination Chemistry An iron-porphyrin, the basic unit of hemoglobin Valdosta State University

  16. Myoglobin / Hemoglobin p.1084

  17. Co atom Coordination Chemistry Vitamin B12 A naturally occurring cobalt-based compound Valdosta State University

  18. Coordination Chemistry • Biological nitrogen fixation contributes about half of total nitrogen input to global agriculture, remainder from Haber process. • To produce the H2 for the Haber process consumes about 1% of the world’s total energy. • A similar process requiring only atmospheric T and P is carried out by N-fixing bacteria, many of which live in symbiotic association with legumes. • N-fixing bacteria use the enzyme nitrogenase — transforms N2 into NH3. • Nitrogenase consists of 2 metalloproteins: one with Fe and the other with Fe and Mo. Valdosta State University

  19. Coordination Chemistry Nickel ion: coordination compounds

  20. Nomenclature • [Ni(NH3)6]2+ • A Ni2+ ion surrounded by 6, neutral NH3 ligands • Gives coordination complex ion with 2+ charge. Ligand: monodentate Coordinate to the metal via a single Lewis base atom.

  21. Inner coordination sphere Nomenclature + Ligand: polydentate also chelating ligands Coordinate with more than one donor atom. (Bidentate) Cl- Co3+ + 2 Cl- + 2 neutral ethylenediamine molecules Cis-dichlorobis(ethylenediamine)cobalt(II) chloride

  22. Bipyridine (bipy) Acetylacetone (acac) Oxalate (ox) Ethylenediamine (en) Bidentate Ligands

  23. Bidentate Ligands Acetylacetonate Complexes Commonly called the “acac” ligand. Forms complexes with all transition elements.

  24. Multidentate Ligands EDTA4- - ethylenediaminetetraacetate ion Multidentate ligands are sometimes called CHELATING ligands

  25. Multidentate Ligands Co2+ complex of EDTA4-

  26. Give the formula of a coordination compound A Co3+ ion bound to one Cl- ion, one ammonia molecule, and two ethylenediamine (en) molecules. • Determine the net charge (sum the charges of the various components). • Place the formula in brackets and the net charge attached. [Co(H2NCH2CH2NH2)2(NH3)Cl]2+

  27. Determine the metal’s oxidation number and coordination number Pt(NH3)2(C2O4) Oxalate: (C2O4)2- Ammonia: NH3 Pt must be 2+ (oxidation number = +2) Coordination number = 4 (two from oxalate and each ammonia filling one). [Co(NH3)5Cl]SO4 Chloride: Cl- Sulfate: SO42- Overall complex must be 2+ Co must be 3+ (oxidation number = +3) Coordination number = 6 (sulfate is not coordinated to the metal).

  28. Nomenclature 1. Positive ions named first 2. Ligand names arranged alphabetically 3. Prefixes -- di, tri, tetra for simple ligands bis, tris, tetrakis for complex ligands 4. If M is in cation, name of metal is used 5. If M is in anion, then use suffix -ate CuCl42- = tetrachlorocuprate 6. Oxidation no. of metal ion indicated in roman numerals. Cis-dichlorobis(ethylenediamine)cobalt(III) chloride

  29. Nomenclature Co(H2O)62+ Hexaaquacobalt(II) Cu(NH3)42+ H2O as a ligand is aqua Tetraamminecopper(II) diamminedichloroplatinum(II) Pt(NH3)2Cl2 NH3 as a ligand is ammine Valdosta State University

  30. Nomenclature Tris(ethylenediamine)nickel(II) IrCl(CO)(PPh3)2 [Ni(NH2C2H4NH2)3]2+ Vaska’s compound Carbonylchlorobis(triphenylphosphine)iridium(I)

  31. Geometry of Coordination Compounds Defined by the arrangement of donor atoms of ligands around the central metal ion. Valdosta State University

  32. Isomerim of Coordination Compounds • Two forms of isomerism • Constitutional • Stereoisomerism • Constitutional • Same empirical formula but different atom-to-atom connections • Stereoisomerism • Same atom-to-atom connections but different arrangement in space. Geometric and Optical

  33. Constitutional Isomers Aldehydes & ketones 3C, 1O, 6H • Coordination isomerism: it is possible to exchange a ligand and the uncoordinated counterion. • Example: [Co(NH3)5Br]SO4 and [Co(NH3)5SO4]Br • (violet)(red) • Linkage isomerism: it is possible to attach a ligand to the metal through different atoms. • Usually: SCN- and NO2-

  34. sunlight Constitutional Isomers Such a transformation could be used as an energy storage device. Pentaamminenitritocobalt(III) Pentaamminenitrocobalt(III) Valdosta State University

  35. cis trans Stereoisomerism • One form is commonly called geometric isomerism or cis-trans isomerism. Occurs often with square planar complexes. Note: there are VERY few tetrahedral complexes. Would not have geometric isomers.

  36. Geometric Isomers Cis and trans-dichlorobis(ethylenediamine)cobalt(II) chloride

  37. Geometric Isomers For octahedral complexes (MX3Y3): fac isomer has three identical ligands lying at the corners of a triangular face of octahedron (fac=facial). mer isomer ligands follow a meridian (mer=meridional). fac isomer mer isomer

  38. Stereoisomers • Enantiomers: stereoisomers that have a non-superimposable mirror image. • Diastereoisomers: stereoisomers that do not have a non-superimposable mirror image (cis-trans isomers). • Asymmetric: lacking in symmetry—will have a non-superimposable mirror image. • Chiral: an asymmetric molecule. Valdosta State University

  39. Enantiomers [Co(NH2C2H4NH2)3]2+

  40. Stereoisomers [Co(en)(NH3)2(H2O)Cl]2+ These two isomers have a plane of symmetry. Not chiral. These two are asymmetric. Have non-superimposable mirror images.

  41. Stereoisomers [Co(en)(NH3)2(H2O)Cl]2+ These are non-superimposable mirror images: enantiomers

  42. Bonding in Coordination Compounds • Model must explain • Basic bonding between M and ligand • Color and color changes • Magnetic behavior • Structure • Two models available • Molecular orbital • Electrostatic crystal field theory • Combination of the two ---> ligand field theory Valdosta State University

  43. Bonding • As ligands L approach the metal ion M+, • L/M+ orbital overlap occurs • L/M+ electron repulsion occurs • Crystal field theory focuses on the latter, while MO theory takes both into account

  44. energy ­ ­ e g 2 2 2 d(x -y ) dz D0 ­ ­ ­ t 2g d d d xy xz yz Ligand Field Theory All electrons have the same energy in the free ion • Consider what happens as 6 ligands approach an Fe3+ ion: Orbitals split into two groups as the ligands approach. Value of ligand field sppliting: ∆o depends on L: e.g., CN- > H2O > Cl-

  45. Octahedral Ligand Field

  46. Tetrahedral and Square Planar Ligand Fields

  47. ­ ­ ­ e energy d d d xy xz yz ­ ­ t 2 2 2 2 d(x -y ) dz Crystal Field Theory • Tetrahedral ligand field. • Note that ∆t = 4/9 ∆o and so ∆t is small. • Therefore, tetrahedral complexes tend to absorb “red wavelengths” and be colored blue. Dt

  48. Ways to Distribute Electrons • For 4 to 7 d electrons in octahedral complexes, there are two ways to distribute the electrons. • High spin — maximum number of unpaired e- • Low spin — minimum number of unpaired e- • Depends size of ∆o and P, the pairing energy. • P = energy required to create e- pair.

  49. e e n n e e r r g g y y ­ ­ e e g g 2 2 2 2 2 2 d d ( ( x x - - y y ) ) d d z z D E s m a l l ­ ­ ­ ­ ­ ­ ­ t t 2 2 g g d d d d d d x x y y x x z z y y z z e n e r g y e g 2 2 2 d ( x - y ) d z D E l a r g e ­ ­ ­ ­ ­ ­ t 2 g d d d x y x z y z Magnetic Properties of Fe2+ • High spin • Weak ligand field strength and/or lower Mn+ charge • D0 is smaller than P • [Fe(H2O)6]2+ Paramagnetic • Low spin • Stronger ligand field strength and/or higher Mn+ charge • D0 is larger than P • [Fe(CN)6]4- Diamagnetic

  50. High and Low Spin Octahedral Complexes High or low spin octahedral complexes only possible for d4, d5, d6, and d7 configurations.