Transition Metals

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
• Fe2 and Fe3
• 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 Ar4s23d5 Mn2 Ar3d5

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 Ar4s13d5 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 ? Mn ne-
• Metal with the most positive reducing potential
  is the best reducing agent
• Sc ? Sc3 3 e- Eored 2.08 V
• Ti ? Ti2 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)5ClCl2
• Brackets hold the complex ion
• (Co(NH3)5Cl2
• The Cl2 outside the brackets are the 2 Cl-
  counterions
• In solution
• Co(NH3)5ClCl2? Co(NH3)5Cl2 2 Cl-

21
Coordination Compounds

• Alfred Werner in the 1890s
• 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)5ClCl2
• Pentaamminechlorocobalt(III) chloride
• K3Fe(CN)6
• Potassium hexacyanoferrate(III)
• Fe(en)2(NO2)22SO4
• Bis(ethylenediamine)dinitroiron(III)sulfate

31
Nomenclature

• Triamminebromoplatinum(II) chloride
• Pt(NH3)3BrCl
• Potassium hexafluorocobaltate(III)
• K3CoF6

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
  (Hunds 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 Field ligands
• 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 Ds.
• DE hc/lfor 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

51
Metallurgy of Iron

• The iron can reduce the CO2
• Fe CO2 ? FeO CO
• So the excess CO2 needs to be removed by adding
  excess coke
• CO2 C ? 2 CO