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Transition Metals & Coordination Chemistry

Transition Metals & Coordination Chemistry. Uses of Transition Metals Iron for steel Copper for wiring and pipes Titanium for paint Silver for photographic paper Platinum for catalysts. Importance of Transition Metals. U.S. imports 60 “strategic and critical” minerals Cobalt

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Transition Metals & Coordination Chemistry

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  1. Transition Metals & Coordination Chemistry • Uses of Transition Metals • Iron for steel • Copper for wiring and pipes • Titanium for paint • Silver for photographic paper • Platinum for catalysts

  2. Importance of Transition Metals • U.S. imports 60 “strategic and critical” minerals • Cobalt • Manganese • Platinum • Palladium • Chromium • Important for economy and defense

  3. Transition Metals and Living Organisms • Iron – transport & storage of O2 • Molybdenum and Iron • Catalysts in nitrogen fixation • Zinc – found in more than 150 biomolecules • Copper and Iron – crucial role in respiratory cycle • Cobalt – found in vitamin B12

  4. Transition Metals: A survey • Representative elements • Chemistry changes across a period • Similarities occur within a group • Transition Metals • Similarities occur within a period as well as within a group • Due to last electrons being “d” (or “f”) orbital electrons

  5. Transition Metals: A Survey • “d” and “f” electrons cannot easily participate in bonding, so chemistry of transition elements are not affected by increased number of these electrons

  6. Transition Metal Behavior • Typical metals • Metallic Luster • Relatively high electrical conductivity • Relatively high thermal conductivity • Silver is the best conductor of heat and electricity • Copper is second best

  7. Properties of Transition Metals • Transition metals vary considerably in some properties • Melting point • W – 3400oC vs. Hg, a liquid at 25oC • Hardness • Iron and Titanium are very hard • Copper, gold, and silver are relatively soft

  8. Properties of Transition Metals • Chemical Reactivity • Reaction with oxygen • Some form oxides that adhere to the metal, protecting the metal from further corrosion • Cr, Ni, Co • Some form oxides that scale off, resulting in exposure of the metal to further corrosion • Fe • Some noble metals do not form oxides readily • Au, Ag, Pt, Pd

  9. Properties of Transition Metals • Forming Ionic Compounds • Transition Metals can form more than one oxidation state • Fe+2 and Fe+3 • Complex Ions • Formed by the cations • The transition metal ion is surrounded by a certain number of ligands (Lewis bases)

  10. Properties of Transition Metals • In forming ionic compounds • Most compounds are colored • Transition metal ion can absorb visible light • Most compounds are paramagnetic • The transition metal ion contains unpaired electrons

  11. Electron Configurations • Energies of the 4s and 3d electrons are very similar • Chromium is an exception to the diagonal rule, can be explained in terms of the similar energies of the 4s and 3d electrons • 4s __ 3d __ __ __ __ __ • Less electron-electron repulsion

  12. Electron Configurations • Transition metal ions • Energy of the 3d orbital in transition metal ions is lower than the energy of the 4s orbital • In other words, in forming a transition metal ion, the electrons are lost from the 4s orbital before the 3d orbitals. • Mn: [Ar]4s23d5 Mn+2: [Ar]3d5

  13. Oxidation States & I.E. • First five transition metals • Maximum possible oxidation state is the result of losing the 4s and the 3d electrons • Cr: [Ar]4s13d5; max. ox. state = +6 • At the end of the period, +2 is the most common oxidation state. • Too hard to remove the d electrons as they become lower in energy as the nuclear charge increases

  14. Standard Reduction Potentials • Metals act as reducing agents • M  M+n + ne- • Metal with the most positive reducing potential is the best reducing agent • Sc  Sc+3 + 3 e- Eored = 2.08 V • Ti  Ti+2 + 2e- Eored = 1.63 V • All the metals except Cu can reduce H+ to H2 • Reducing ability decreases going across the period

  15. 4d and 5d Transition Series • Radius increases in going from 3d to the 4d metals • Radius of the 4d metals is similar to the 5d metals due to the lanthanide contraction

  16. Lanthanide Contraction • Adding 4f electrons does not add to the size of the atom (as inner electrons) • However, nuclear charge is still increasing. • Increased nuclear charge offsets the normal increase in size in filling the next higher energy level • Chemistry of 4d and 5d elements are very similar

  17. 4d and 5d transition metals • Zr and ZrO2 – great resistance to high temperature, used for space vehicle parts exposed to high temperatures of reentry • Niobium and Molybdenum – important alloying materials for steel • Tantalum – resists attacks by body fluids, used for replacement of bones • Platinum group: Ru, Os, Rh, Ir, Pd, Pt • Used as catalysts

  18. Read • Pg. 971 – 977 • Look at pictures, note colors

  19. Coordination Compounds • Coordination compound • Formed by transition metal ions • Usually colored • Often paramagnetic • Consists of • A complex ion • Made up of the transition metal ion with its attached ligands • Counterions (the anions or cations needed to produce a neutral compound)

  20. Coordination Compounds • [Co(NH3)5Cl]Cl2 • Brackets hold the complex ion • (Co(NH3)5Cl+2 • The “Cl2” outside the brackets are the 2 Cl- counterions • In solution: • [Co(NH3)5Cl]Cl2 Co(NH3)5Cl+2 + 2 Cl-

  21. Coordination Compounds • Alfred Werner in the 1890’s • Transition metals have two types of valence (combining abilities) • Primary valence – ability to form ionic bonds with oppositely charged ions • Secondary valence – ability to to bind to Lewis bases (ligands) to form complex ions

  22. Coordination Compounds • Primary Valence = Oxidation State • Secondary Valence = Coordination Number • number of bonds formed between the metal ion and the ligands in the complex ion.

  23. Coordination Number • Coordination number • Varies from two to eight • Depends on the size, charge, and electron configuration of the transition metal • Most common coordination number is 6 • Next is 4, then 2 • Many metals show more than one coordination number • No way to predict which coordination number

  24. Coordination Compounds • 6 ligands – octahedral geometry • 4 ligands – square planar or tetrahedral geometry • 2 ligands - linear

  25. Ligands • Ligand • Neutral molecule or ion having a lone electron pair that can be used to form a bond with a metal ion • Metal-ligand bond • Interaction between a Lewis acid and a Lewis base • Also known as a coordinate covalent bond

  26. Ligands • Unidentate (one tooth) ligand • Can only form one bond with the metal ion • H2O, CN-, NH3, NO2-, SCN-, OH-, Cl-, etc • Bidentate ligand • Can form two bonds to a metal • Ethylenediamine, aka en, (H2N-CH2- CH2-NH2), oxalate

  27. Ligands • Polydentate ligands (chelating ligands) • EDTA, ethylenediaminetetraacetate • Surrounds the metal • Forms very stable complex ions with most metal ions • Used as a scavenger to remove toxic heavy metals, e.g., lead, from the body • Found in numerous consumer products to tie up trace metal ions

  28. Nomenclature • Cation is named before the anion • Ligands are named before the metal ion • Naming ligands • Add an o to the root name of an anion (fluoro, chloro, hydroxo, cyano, etc.) • Neutral ligand, use the name of the molecule except for the following: • H2O = aqua • NH3 = ammine • CH3NH2 = methylamine • CO = carbonyl • NO = nitro

  29. Nomenclature • Use prefixes to indicate number of simple ligands (mono, di, tri, tetra, penta, hexa) Use bis, tris, tetrakis for complicated ligands that already contain di, tri, etc) • Oxidation state of central metal ion is designated by a Roman numeral in parentheses • When more than one type of ligand is present, they are named alphabetically, where prefixes do not affect the order. • If the complex ion has a negative charge, add –ate to the name of the metal (eg. ferrate or cuprate)

  30. Nomenclature • [Co(NH3)5Cl]Cl2 • Pentaamminechlorocobalt(III) chloride • K3Fe(CN)6 • Potassium hexacyanoferrate(III) • [Fe(en)2(NO2)2]2SO4 • Bis(ethylenediamine)dinitroiron(III)sulfate

  31. Nomenclature • Triamminebromoplatinum(II) chloride • [Pt(NH3)3Br]Cl • Potassium hexafluorocobaltate(III) • K3[CoF6]

  32. The Crystal Field Model and Bonding in Complex Ions • Crystal field model focuses on the energies of the d orbitals • Color and magnetism of complex ions are due to changes in the energies of the d orbitals caused by the metal-ligand interaction

  33. The Crystal Field Model • Crystal Field Model assumes • Ligands are like negative point charges • Metal-ligand bonding is entirely ionic • In the free metal ion, all the d orbitals are degenerate, they have the same energies

  34. The Crystal Field Model • In the complex ion, the d orbitals are split into two sets with two different energies. • Lower energy set • The negative point charge ligands are farthest from the dxz, dyz, and dxy orbitals (the orbitals that point between the ligands) • Electron pair repulsions are minimized

  35. The Crystal Field Model • In the complex ion, the d orbitals are split into two sets with two different energies. • Higher energy set • dz2, dx2-y2 point at the ligands • More electron repulsions

  36. The Crystal Field Model • Splitting of the 3d orbital energies • Results in the color and magnetism of the complex ions

  37. The Crystal Field Model • Strong field case (or low spin case) • Splitting produced by the liqands is very large • Electrons will pair in the lower energy orbitals (the ones pointing between the ligands) • Result – a diamagnetic complex in which all electrons are paired

  38. The Crystal Field Model • Weak Field Case (or high spin case) • Splitting produced by the ligands is very small • Electrons will fill each of the five d orbitals (Hund’s rule) before pairing • Will result in paramagnetism with unpaired electrons

  39. The Crystal Field Model • Ligands have different abilities to produce d-orbital splitting • Strong Field ligands -----> Weak Fieldligands • Large D -------> Small D • CN- > NO2- > en > NH3 > H2O > OH- > F-> Cl- > Br- > I- • D increases as the charge on the metal ion increases • Larger charge on ion pulls the ligands closer, results in greater splitting to minimize repulsions

  40. The Crystal Field Model and Colors • Colors of complex ions • A complex ion will absorb certain wavelengths of light • The color we see is complementary to the color absorbed. • If yellow and green light is absorbed, then red and blue light passes through, so we would see violet.

  41. The Crystal Field Model and Colors • A complex ion will absorb a specific wavelength depending on the D between the d orbitals. • Different ligands on the same metal ion will result in different colors because of the different D’s. • DE = hc/l…for octahedral complex ions, the l is usually in the visible region

  42. Metallurgy • Steps in the process of separating a metal from its ore (metallurgy) • Mining • Pretreatment of the ore • Reduction to the free metal • Purification of the metal (refining) • Alloying

  43. Metallurgy • Ores are mixtures containing • Minerals (relatively pure metal compounds) • Gangue (sand, clay, and rock) • After mining, treat ores to remove the gangue and concentrate the mineral • Pulverize and process ore

  44. Metallurgy • Flotation process • Allows minerals to float to the surface of a water-oil-detergent mixture • Alter the mineral to prepare it for the reduction step • Carbonates and hydroxides are heated • CaCO3 CaO + CO2 • Mg(OH)2  MgO + H2O

  45. Metallurgy • Sulfides are converted to oxides by heating in air at temperatures below their melting points (roasting) • 2 ZnS + 3 O2 2 ZnO + 2 SO2

  46. Metallurgy • Smelting – method used to reduce the metal ion to the free metal • Depends on the affinity of the metal ion for electrons • Good oxidizing agents produce the free metal in the roasting process HgS + O2 Hg(l) + SO2

  47. Metallurgy • More active metals • Use coke (impure carbon), carbon monoxide, or hydrogen, as a strong reducing agent • Fe2O3 + 3 CO  2 Fe + 3 CO2 • WO3 + 3 H2  W(l) + 3 H2O • ZnO + C  Zn(l) + CO

  48. Metallurgy • Most active metals (Al and alkali metals) • must be reduced electrolytically from the molten salts.

  49. Metallurgy of Iron • Iron ores • pyrite (FeS2), siderite (FeCO3), hematite(Fe2O3, magnetite (Fe3O4) • Concentrate iron in iron ores • Separate Fe3O4 mineral from the gangue by magnets • Iron ores that are not magnetic are converted to Fe3O4, or are concentrated using the flotation process

  50. Metallurgy of Iron • Reduction process • Occurs in the blast furnace • Uses coke which is converted to CO in the blast furnace • Reduction occurs in steps: • 3Fe2O3 + CO  2 Fe3O4 + CO2 • Fe3O4 + CO  3 FeO + CO2 • FeO + CO  Fe + CO2

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