George Mason University

1
George Mason University General Chemistry
212 Chapter 23 Transition Elements Acknowledgemen
ts Course Text Chemistry the Molecular Nature
of Matter and Change, 6th ed, 2011, Martin S.
Silberberg, McGraw-Hill The Chemistry 211/212
General Chemistry courses taught at George Mason
are intended for those students enrolled in a
science /engineering oriented curricula, with
particular emphasis on chemistry, biochemistry,
and biology The material on these slides is taken
primarily from the course text but the instructor
has modified, condensed, or otherwise reorganized
selected material.Additional material from other
sources may also be included. Interpretation of
course material to clarify concepts and solutions
to problems is the sole responsibility of this
instructor.
2
Transition Elements

• Properties of the Transition Elements
• The Inner Transition Elements
• Highlights of Selected Transition Elements
• Coordination Compounds
• Theoretical Basis for the Bonding and Properties
  of Complexes

3
Transition Elements

• Main-Group vs Transition Elements
• Most important uses of Main-Group elements
  involve the compounds made up of these elements
• Transition Elements are highly useful in their
  elemental or uncombined form

4
Transition Elements

• Properties of Transition Elements
• Recall The A (Main Group) elements make up the
  s and p blocks
• Transition Elements make up the
• d block (B group)
• f block elements (Inner Transition Elements)
• As ions, transition metals (elements) provide
  fascinating insights into chemical bonding and
  structure
• Transition metals play an important role in
  living organisms

5
Transition Elements
6
Transition Elements

• Electron Configurations of the Transition Metals
• In the Periodic Table, the Transition metals,
  designated d-block (B-Group) elements, are
  located in
• 40 elements in 4 series within Periods 4 -7
• Lie between the last ns-block elements in group
  2A(2) (Ca Ra) and the first np-block elements
  in group (3A(13) (Ga element 113 (unnamed)
• Each series represents the filling of the 5 d
  orbitals
• l 2 ? ml -2 -1 0 1 2
• (5 orbitals per period x 2 electrons per orbital
  x 4 Periods
• 40 Elements

7
Transition Elements

• Condensed d-block ground-state electron
  configuration
• noble gas ns2(n-1)dx, with n 4 -7 x 1-10
• (several aufbau build-up exceptions)
• Partial (valence shell) electron configuration
• ns2(n-1)dx
• Recall Chromium (Cr) and Copper (Cu) are
  exceptions to the above aufbau configuration
  setup
• Expected Cr Ar 4s23d4 Cu Ar 4s23d9
• Actual Cr Ar 4s13d5 Cu Ar 4s13d10
• Reasons change in relative energies of 4s 3d
  orbitals and the unusual stability of ½ filled
  and filled sublevels (level 4 relative to level
  3)

8
Transition Elements
Note Aufbau build up exceptions for Cr Cu
9
Transition Elements

• The Inner Transition elements
• Lie between the 1st and 2nd members of the
  d-block elements in Periods 6 7 (n6 n7)
• Condensed f-block ground-state electron
  configuration (Periods 6 7)
• noble gas ns2 (n-2)f14(n-1)dx, with n 6 -7
• The 28 f orbitals are filled as follows
• l 3 ? ml -3 -2 -1 0 1 2
  3
• 7 orbitals per period x 2 electrons per orbital x
  2 periods
• 28 Elements

10
Transition Elements

• Transition Metal Ions
• Form through the loss of the ns
  electronsbefore the (n-1)d electrons
• Ex. Ti2 Ar 3d2 4s2 ? Ar 3d2 2e-
  (not Ar 4s2)
• (Ti2 also called d2 ion)
• Ions of different transition metals with the same
  electron configuration often have similar
  properties
• Ex. Mn2 and Fe3 are both d5 ions
• Mn2 Ar 3d54s2 ? Ar 3d5 2e-
• Fe3 Ar 3d64s2 ? Ar 3d5 3e-
• Both Ions have pale colors in aqueous solutions
• Both form complex ions with similar magnetic
  properties

11
Practice Problem

• Write condensed electron configurations for the
  following ions
• Zr V3 Mo3
• Vanadium (V)
  Period 4
• Zirconium (Zr) Molybdenum (Mo) Period 5
• General Configuration ns2(n-1)dx
• a. Zr is 2nd element in the 4d series Kr
  5s24d2 (d2 ion)
• b. V is the 3rd element in the 3d series Ar
  4s23d3
• ns electrons lost first
• In forming V3, 3 electrons lost two 4s one
  3d
• ? V3 Ar 4s23d3 ? Ar 3d2 (d2 ion)
  3e-
• c. Mo lies below Cr in Period 5, Group 6B(6)
  kr 5s1 4d5
• Note Same electron configuration exception as
  Cr
• ? Mo3 Kr 5s1 4d5 ? Kr 4d3 (d3 ion)
  3 e-

12
Transition Elements

• Trends of Transition Elements Across a Period
• Transition elements exhibit smaller, less regular
  changes in
• Size
• Electronegativity
• First Ionization Energy
• than the Main Group Elements in the same group

13
Transition Elements

• Atomic Size
• General overall decrease across a period for both
  Main group and Transition group elements
• As the d orbitals are filled across a period,
  the change in atomic size within the transition
  elements evens out because the increased nuclear
  charge shields the outer electrons preventing
  them from spreading out

Transition Metals
Main group
Main group
14
Transition Elements

• Electronegativity
• Electronegativity generally increases across
  period
• Change in electronegativity within a series
  (period) is relatively small in keeping with the
  relatively small change in size
• Small electronegativity change in Transition
  Elements is in contrast with the steeper increase
  between the Main Group elements across a period
• Magnitude of Electronegativity in Transition
  elements is similar to the larger main-group
  metals

Transition Metals
15
Transition Elements

• Ionization Energy
• Ionization Energy of Period 4 Main-group elements
  rise steeply from left to right as the electrons
  become more difficult to remove from the poorly
  shielded increasing nuclear charge, i.e., no d
  electrons
• In the Transition metals, however, the first
  ionization energies increase relatively little
  because of the effective shielding by the inner
  d electrons reducing the effect of the
  increased nuclear charge

Transition Metals
16
Transition Elements

• Trends Within (down) a Group (relative to
  main-group elements)
• Vertical trends differ from those of the Main
  Group elements
• Atomic Size
• Increases, as expected, from Period 4 to 5
• No increase from Period 5 to 6
• Lanthanides, starting in period 6 with buried
  4f sublevel orbitals, appear between the 4d
  orbitals in period 5 and the 5d orbitals in
  period 6 Aufbau buildup sequence
• An element in Period 6 is separated from the one
  above it in Period 5 by 32 electrons
• (ten 4d, six 5p, two 6s, and fourteen 4f)
• The extra shrinking that results from the
  increased nuclear charge due to the addition of
  the fourteen 4f electrons is called the
• Lanthanide Contraction

17
Transition Elements
Note n gt 7 l gt 3 Sublevels not utilized for
any element in the current Period Table
n5
18
Transition Elements
Main Group Non-metals
Main Group Metals
Transition Metals
Inner Transition Metals
Order of Sublevel Orbital Filling
19
Transition Elements

• Trends Within a Group (relative to main-group
  elements)
• Electronegativity (EN) Relative ability of an
  atom in a covalent bond to attract shared
  electrons
• EN of Main-group elements decreases down group
• greater size means less attraction by nucleus
• Greater Reactivity
• EN in Transition elements is opposite the trend
  in Main-group elements
• EN increases from period 4 to period 5
• No change from period 5 to period 6, since the
  change in volume is small and Zeff increases (f
  orbital electrons)
• Transition metals exhibit more covalent bonding
  and attract electrons more strongly than
  main-group metals
• The EN values in the heavy metals exceed those of
  most metalloids, forming salt-like compounds,
  such as CsAu and the Au- ion

20
Transition Elements

• Trends Within a Group (relative to Main-group
  elements)
• Ionization Energy Energy required to remove an
  electron from a gaseous atom or ion
• Main-group elements increase in size down a
  group, decreasing the Zeff , making it
  relatively easier to remove the outer electrons
• The relatively small increase in size of
  transition metals, combined with the relatively
  large increase in nuclear charge (Zeff), makes it
  more difficult to remove a valence electron,
  resulting in a general increase in the first
  ionization energy down a group

21
Transition Elements

• Trends Within a Group (relative to Main-group
  elements)
• Density
• Atomic size (volume) is inversely related to
  density
• (As size increases density decreases)
• Transition element density across a period
  initially increases, then levels off, finally
  dips at end of series
• From Period 5 to Period 6 the density increases
  dramatically because atomic volumes change little
  while nuclear mass increases significantly
• Period 6 series contains some of the densest
  elements known
• Tungsten, Rhenium, Osmium, Iridium, Platinum,
  Gold
• (Density 20 times greater than water,
• 2 times more dense than lead)

22
Transition Elements

• Trends are unlike those for the Main-group
  elements in several ways
• 2nd 3rd members of a transition group are
  nearly same size
• Electronegativity increases down a transition
  group
• 1st ionization energies are highest at the bottom
  of transition group
• Densities increase down a transition group (mass
  increases faster than density

23
Transition Elements

• Chemical Properties of the Transition Elements
• Atomic physical properties of Transitions
  elements are similar to Main group elements
• Chemical properties of transition elements are
  very different from main group elements
• Oxidation States
• Main-group elements display one, or at most two,
  oxidation states
• The ns (n-1)d electrons in transition
  elements are very close in energy
• All or most can be used as valence electrons in
  bonding Transition metals can have multiple
  oxidation states

24
Transition Elements
Oxidation State (Number) Magnitude of charge an
atom in a covalent compound would have if its
shared electrons were held completely by the atom
that attracts them more strongly
Note All 3 d5
Ex. MnO2 O.N. Mn 4
Ex. MnO4- O.N. Mn 7
25
Transition Elements

• Metallic Behavior
• Atomic size and oxidation state have a major
  effect on the nature of bonding in transition
  metal compounds
• Transition elements in their lower oxidation
  states behave more like metals Oxides more
  basic
• Transition elements in their higher oxidation
  states exhibit more covalent bonding Oxides
  more acidic
• Ex. TiCl2 (Ti2) is an ionic solid
• TiCl4 (Ti4) is a molecular liquid

26
Transition Elements

• Metallic Behavior
• In the higher oxidation states
• The atoms have fewer electrons
• The nuclear charge pulls remaining electrons
  closer, decreasing the volume and increasing the
  density
• The charge density (ratio of the ions charge to
  its volume) increases
• The increase in charge density leads to more
  polarization of the electron clouds in non-metals
  
• The bonding becomes more covalent
• The stronger the covalent bond, the less metallic
• The oxides, therefore, become less basic
• Ex. TiO (Ti2) is weakly basic in water
• TiO2 (Ti4) is amphoteric, reacting with both
  acid and base

27
Transition Elements

• Electronegativity, Oxidation State,
  Acidity/Basicity
• Why does oxide acidity increase with oxidation
  state?
• Metal with a higher oxidation state is more
  positively charged
• Attraction of electrons is increased, i.e.,
  electronegativity increases
• Effective Electronegativity Valence State
  Electronegativity
• EN Cr 1.6 Al 1.5 (basic oxide)
  Cr3 1.7 Cr6 2.3 P 2.1
  (acidic oxides)

28
Transition Elements

• Metallic Behavior
• Reduction Strength (Redox)
• Standard Electrode Potential, Eo , generally
  decreases across a period
• As the value of Eo becomes more negative, i.e.,
  at the beginning of the series, the ability of
  the species to act as a reducing agent increases
• Thus, Ti2, Eo -01.63V, is a stronger reducing
  agent than Ni2, Eo -0.25V

• All species with a negative value of Eo can
  reduce H
• 2H(aq) 2e- ? H2(g) Eo 0.0V)
• Note Cu2 (Eo 0.34 V) cannot reduce H
• The magnitude of the Eo values between two
  species, and the relative degree of surface
  oxidation, determines the level of reactivity of
  the oxidation/reduction reaction in water, steam,
  or acid solution

29
Transition Elements

• Color in Transition Elements
• Most Main-Group Ionic Compounds are colorless
• Metal ions have a filled outer shell
• With only much higher energy orbitals available
  to receive an excited electron, the ion does
  not absorb visible light
• The partially filled d orbitals of the
  transition metals can absorb visible wavelengths
  and move to slightly higher energy d levels

30
Transition Elements

• Magnetism in Transition Elements
• Magnetic properties are related to electron
  sublevel occupancy
• A Paramagnetic substance has atoms or ions with
  unpaired electrons
• A Diamagnetic substance has atoms or ions with
  only paired electrons
• Most Main-Group metal ions are diamagnetic
  (filled outer shells)
• Many Transition metal compounds are paramagnetic
  because of unpaired electron in the d subshells

31
Transition Elements

• Chemical Behavior Within a Group
• Main_Group
• The decrease in Ionization Energy (IE) going down
  a group results in increased reactivtiy
• Transition metals
• Ionization Energy increases down group
• The Standard Electrode Potential (Eo) also
  increases (becomes more positive)
• ?Chromium is stronger reducing agent

32
Transition Elements

• The Inner Transition Elements
• Lanthanides (Rare Earth Elements)
• (Cerium (Ce) Z 58 Lutetium (Lu) Z 71)
• Silvery, high melting point (800 1600oC) metals
• Small variations in chemical properties makes
  them difficult to separate
• Occur naturally in the 3 oxidation state as M3
  ions of very similar radii
• Most lanthanides have the ground-state electron
  configuration filling the f subshell level
• Xe 6s2 4fx 5d0 x varies across series
  (Period)
• Exceptions Ce, Gd, Lu have single e- in 5d
  orbital

33
Sample Problem

• Finding the Number of Unpaired Electrons
• The alloy SmCo5 forms a permanent magnet because
  both Samarium and Cobalt have unpaired electrons
• How many unpaired electrons are in the Sm atom
  (Z62)?
• Ans
• Samarium is the eighth element after Xe (Noble
  Shell)
• Xe 6s2 4f6
• Two (2) electrons go in the 6s sublevel
• In general, the 4f sublevel fills before the 5d
  sublevel (slide 17)
• Recall previous slide - only Ce, Gd, Lu have
  5d electrons
• ? Remaining 6 electrons go into the 4f orbitals

6s
4f
5d
6p
Six unpaired electrons
34
Transition Elements

• The Actinides
• (Thorium (Th) Z90 - Lawrencium Z103)
• All Actinides are Radioactive (Alpha (4He2)
  Decay
• Only Thorium Uranium occur in nature
• Share very similar chemical physical properties
• Silvery and chemically reactive
• Principal oxidation state is 3, similar to
  lanthanides

35
Transition Elements

• Highlights of Selected Transition Metals
• Period 4 Chromium Manganese
• Chromium
• Silvery, shiny metal with many colorful compounds
• Cr2O3 acts as protective coating on easily
  corroded (oxidized) metals, such as iron
• Stainless steels contain as much as 18 Cr,
  making them highly resistant to corrosion
• Electron Configuration (Ar 4s1 3d5) with 6
  valence electrons occurs in all possible positive
  oxidation states
• Important ions Cr2, Cr3, Cr6
• Non-metallic character and oxide acidity increase
  with metal oxidation state
• Cr2 potential reducing agent (Cr loses
  additional electrons)
• Cr6 potential oxidizing agent (Cr gains
  electrons)

36
Transition Elements

• Highlights of Selected Transition Metals
• Chromium
• Chromium (II) Cr2
• CrO is basic and largely ionic
• Forms insoluble hydroxide in neutral or basic
  solution
• Dissolves in acid to yield Cr2 ion and water
• CrO(s) 2H ? Cr2 (aq) H2O(l)
• Chromium(III) Cr3
• Cr2O3 is amphoteric, similar properties as
  Aluminum
• Dissolves in acid to yield violet Cr3 ion
• Cr2O3(s) 6H(aq) ? 2Cr3(aq) 3H2O(l)
• Reacts with base to form the green Cr(OH)4- ion
• Cr2O3(s) 3H2O OH- ? 2Cr(OH)4-(aq)

37
Transition Elements

• Highlights of Selected Transition Metals
• Chromium (cont)
• Chromium (VI) - Cr6 (Deep Red)
• CrO3 is covalent and acidic
• Dissolves in water to form Chromic Acid (H2CrO4)
• CrO3(s) H2O(l) ? H2CrO4(aq)
• H2CrO4 yields yellow Chromate ion (CrO42-) in
  base
• H2CrO4(aq) 2OH(l) ? CrO42-(aq) 2H2O(l)
• Chromate ion forms orange dichromate (Cr2O72-)
  ion in acid
• 2CrO42-(aq) 2H(aq) ? Cr2O72-(aq) H2O(l)

38
Transition Elements

• Highlights of Selected Transition Metals
• Manganese
• Hard and Shiny
• Like Vanadium Chromium used to make steel
  alloys
• Chemistry of Manganese is similar to Chromium
• Metal reduces H from acids to form Mn2 ion
• Mn(s) 2H(aq) ? Mn2(aq) H2(g) Eo
  1.18 V
• Manganese can use all its valence electrons
  (several oxidation states) to form compounds
• Mn2 Mn4 Mn7 most important
• As oxidation state rises from 2 to 7, the
  valence state electronegativity increases and the
  oxides of Mn change from basic to acidic
• Mn(II)O (basic) Mn(III)2O3
  (amphoteric)
• Mn(IV)O2 (insoluble) Mn(VII)2O7 (acidic)

39
Transition Elements

• All Manganese species with oxidation states
  greater than 2 act as oxidizing agents (gaining
  the electrons lost by the atoms being oxidized)
• Mn7O4-(aq) 4H 3e- ? Mn4O2(s)
  2H2O(l) Eo 1.68
• Mn7O4-(aq) 2H2O 3e- ? Mn4O2(s) 4OH-
  Eo 0.59
• (Mn7O4- is a much stronger oxidizing agent in
  acid solution than in basic solution note
  difference in Eo values)

40
Transition Elements

• Manganese
• Unlike Cr2 Fe2, the Mn2 (3d5) ion resists
  oxidation in air
• Recall half-filled (-1/2 spin electrons missing)
  filled sublevels are more stable than partially
  filled sublevels
• Cr2 is a d4 species and readily loses a 3d
  electron to form the d3 ion Cr3, which is more
  stable
• Fe2 is a d6 species and removing a 3d electron
  yields the stable, half-filled d5 configuration
  of Fe3
• Removing an electron from Mn2 disrupts the more
  stable d5 configuration

41
Transition Elements TheirCoordination Compounds

• Coordination Compounds (Complexes)
• Most distinctive aspect of transition metal
  chemistry
• Complex Substances that contain at least one
  complex ion
• Complex ion Species consisting of a central
  metal cation (either a main-group or transition
  metal) that is bonded to molecules and/or anions
  called Ligands
• The Complex ion is typically associated with
  other (counter) ions to maintain neutrality
• A coordination compound behaves like an
  electrolyte in water
• Complex ion and counter ion separate
• Complex ion behaves like a polyatomic ion the
  ligands and central atom remain attached

42
Transition Elements TheirCoordination Compounds

• Components of Coordination Compound
• When solid complex dissolves in water, the
  complex ion and the counter ions separate, but
  ligands remain bound to central atom

Co(NH3)6Cl3(s)
Octahedral Geometry
Central Atom
Ligands
Counter Ions
43
Transition Elements TheirCoordination Compounds

• Complex ions
• A complex ion is described by the metal ion and
  the number and types of ligands attached to it
• The bonding between metal and ligand generally
  involves formal donation of one or more of the
  ligand's electron pairs
• The metal-ligand bonding can range from covalent
  to more ionic
• Furthermore, the metal-ligand bond order can
  range from one to three (single, double, triple
  bonds)
• Ligands are viewed as Lewis Bases (donate
  electron pairs), although rare cases are known
  involving Lewis acidic ligands

44
Transition Elements TheirCoordination Compounds

• Complex ions
• The complex ion structure is related to three
  characteristics
• Coordination Numbers
• The number of ligand atoms that are bonded
  directly to the central metal ion
• Coordination number is specific for a given metal
  ion in a particular oxidation state and compound
• Coordination number in Co(NH3)63 is 6
• The most common coordination number in complex
  ions is 6, but 2 and 4 are common, with a few
  higher

45
Transition Elements TheirCoordination Compounds

• Complex ions
• Geometry Depends on Coordination No. Nature
  of Metal Ion

d8
d1

d3

d9
d5

d10
d6

46
Transition Elements TheirCoordination Compounds

• Complex Ions
• Donor Atoms per Ligand
• The Ligands of complex ions are molecules or
  anions with one or more donor atoms that each
  donate a lone pair of electrons to the metal ion
  to form a covalent bond
• Atoms with lone pairs of electrons often come
  from Groups 5A, 6A, or 7A (main-group elements)

47
Transition Elements TheirCoordination Compounds

• Complex Ions
• Ligands are classified in terms of the number of
  donor atoms (teeth) that each uses to bond to the
  central metal ion
• Monodentate Ligands use a single donor atom
• Bidentate Ligands have two donor atoms
• Polydentate Ligands have more than two donor
  atoms

48
Transition Elements TheirCoordination Compounds
Donor Atom
The Ligands contains one or more Donor atoms that
have electron pairs to donate to the Central Atom
49
Transition Elements TheirCoordination Compounds

• Complex Ions
• Chelates (Greek chela crabs claw)
• Bidentate and Polydentate ligands give rise to
  rings in the complex ion
• Ex Ethylene Diamine (abbreviated (en) in
  formulas)
• (N C C N)
• forms a 5-member ring, with the two electron
  donatingN atoms bonding to the metal atom
• Such ligands seem to grab the metal ion like
  claws

Ethylenediaminetetraacetate (EDTA)
Used in treating heavy-metal poisoning, by acting
as a scavenger of lead and other heavy-metal
ions, removing them from blood and other body
fluids
50
Transition Elements TheirCoordination Compounds

• Formulas and Names of Coordination Compounds
• Important rules for writing formulas of
  coordinate compounds
• The cation is written before the anion
• The charge of the cation(s) is balanced by the
  charge of the anions
• In the complex ion, neutral ligands are written
  before anionic ligands
• The entire ion is placed in brackets, i.e.,

51
Transition Elements TheirCoordination Compounds

• Formulas and Names of Coordination Compounds
• Coordination Compound Formulas
• Example 1
• Two compound cations (K) Total Charge 2
• Ion Central Metal Cation (Co2) Total Charge
  2
• Neutral Ligands (2 NH3) Total Charge 0
• Counter Ions (4 Cl-) Total Charge -4
• Net Charge on Complex Ion - 2 Co(NH3)2Cl4-2

52
Transition Elements TheirCoordination Compounds

• Formulas and Names of Coordination Compounds
• Coordination Compound Formulas
• Example 2 Complex Ion and Counter Ion
• Co(NH3)4Cl2Cl
• Counter Ion (Cl-) (not part of complex ion)
  Total charge -1
• Complex Ion - Neutral Ligands (4 NH3)
  Total Charge 0
• Complex Ion - Anion Ligands (2 Cl-)
  Total Charge -2
• Complex Ion - Co(NH3)4Cl2 Total Charge
  1
• Complex Ion - Central Metal Atom (Co) Total
  Charge 3
• Co3(NH3)4Cl-2Cl-

53
Transition Elements TheirCoordination Compounds

• Formulas and Names of Coordination Compounds
• Example 3 Complex Cation and Complex Anion
• Co(NH3)5Br2Fe(CN)6
• Complex Cation - Co(NH3)5Br2
• Complex Cation Central Atom (Co3) Total
  charge 3
• Complex Cation Neutral Ligands (5 NH3) Total
  Charge 0
• Complex Cation Anionic Ligand (Br-) Total
  Charge -1
• Complex Anion (Fe(CN)64-) Total Charge -4
• Complex Anion Central Cation (Fe2) Total
  Charge 2
• Complex Anion Ligand (6 CN-1) Total Charge -6
  
• Co3(NH3)5Br-2Fe2(CN-)6
• 2 x (3 -1) 4 2 - 6 -4

54
Transition Elements TheirCoordination Compounds

• Formulas and Names of Coordination Compounds
• Naming Coordination Compounds
• Rules
• The Cation is named before the Anion
• Within the Complex Ion, the Ligands are named, in
  alphabetical order, before the metal ion
• Neutral Ligands generally have the molecule name,
  with exceptions Ex NH3 (ammine), H2O (aqua), CO
  (carbonyl)
• Anionic Ligands drop the ide and add o after
  the root name Ex. Cl- becomes chloro
• A numerical prefix indicates the number of
  ligands of a particular type Ex di (2), tri
  (3), tetra (4)
• Co(NH3)4Cl2Cl
• Tetra ammine di chloro cobalt(III)chloride
• m

55
Transition Elements TheirCoordination Compounds

• Formulas and Names of Coordination Compounds

Names of Some Neutral and Anionic Ligands
Names of Some Metals Ions in Complex Anions
Numerical Prefixes used In Complex Anions
56
Transition Elements TheirCoordination Compounds

• Formulas and Names of Coordination Compounds
• Naming Coordination Compounds
• Rules
• Some ligand names already contain a numerical
  prefix
• Ethylenediamine
• In these cases the number of ligands is
  indicated by such terms as
• bis (2) tris(3) tetrakis(4)
• A compound with two ethylene ligands would
  contain the following ligand name
• bis(ethylenediamine)

57
Transition Elements TheirCoordination Compounds

• Formulas and Names of Coordination Compounds
• Naming Coordination Compounds
• Rules
• The oxidation state of the central metal ion is
  given by a Roman numeral (in parentheses) only if
  the metal ion can have more than one state, as in
  the compound
• Co(NH3)4Cl2Cl Co3(NH3)4Cl-2Cl-
• Tetra ammine di chloro cobalt(III)chloride
• If the complex ion is an anion, drop the ending
  of the Central metal name and add ate
• KPt(NH3)Cl5 KPt4(NH3)Cl-5-
• Potassium ammine penta chloro platinate(IV)
• Na4FeBr6 Na4Fe2Br-6
• Sodium hexa bromo ferrate(II)

58
Practice Problem

• What is the systematic name of Na3AlF6?
• Ans Complex ion AlF63-
• Ligands 6 (hexa) F- ions (Fluoro)
• Complex ion is an anion (net charge -3)
• End of metal ion Aluminum must be changed to
  ate
• Complex ion name hexafluoroaluminate
• Aluminum has only the 3 oxidation state so
  Roman numerals are not required
• Na3 is the positive counter ion it is
  separated from the complex anion by a space
• Na3AlF6 Sodium Hexfluoroaluminate

59
Practice Problem

• What is the systematic name of Co(en)2Cl2NO3?
• Ans Listed alphabetically, there are two Cl-
  (dichloro) and two en bis(ethylenediamine)
  ligands
• Note Alphabetically refers to the root chemical
  names
• Chloro Ethylenediamine
• The Complex ion is a Cation, with a charge
  of 1
• Co3(en)2Cl-2
• The metal name in a complex ion is unchanged -
  Cobalt
• Because Cobalt can have several oxidation
  states, its charge must be specified - Cobalt
  (III)
• One Nitrate ion (NO-3) balances the 1 complex
  cation
• Dichloro bis (ethylene diamine)cobalt(III)
  nitrate

60
Practice Problem

• What is the formula of
• Tetra ammine bromo chlroro platinum(IV) chloride
• Ans The central atom of the complex cation is
  written first
• Platinate(IV) Pt4
• The ligands follow in alphabetical order of root
  chemical name
• Tetraammine (NH3) Bromo (Br-) Chloro (Cl-)
• Complex ion formula - Pt(NH3)4BrCl2
  Pt4(NH3)4Br-Cl-2
• To balance the 2 charge of the complex
  cation, 2 Cl- counter ions are required
• Pt(NH3)4BrClCl2

61
Practice Problem

• What is the formula of
• Hexa ammine cobalt(III) tetra chloro ferrate(III)
• Ans Compound consists of two complex ions
• Complex Cation Six hexammine (NH3)
  cobalt(III) (Co3)
• Complex Cation Co(NH3)63
  Co3(NH3)63
• Complex Anion tetrachloro - 4 Cl-
• Complex Anion ferrate(III) - Fe3
• Complex Anion FeCl-4-
• Complex cation balanced by 3 complex anions
• Coordinate Compound Co(NH3)6FeCl4-3

62
Transition Elements TheirCoordination Compounds

• Isomerism in Coordination Compounds
• Isomers are compounds with the same chemical
  formula but different properties
• Constitutional (Structural) Isomers
• Two compounds with the same formula, but with
  atoms connected differently
• Two Types
• Coordination Isomers Composition of the complex
  ion changes but not the compound
• Ex. Ligand and counter ion exchange positions
• Pt(NH3)4Cl2(NO2)2 Pt(NH3)4(NO2)2Cl2
• Ex. Two sets of ligands reversed
• Cr(NH3)6Co(CN)6 Co(NH3)6Cr(CN)6
• (NH3 is ligand of Cr3 in one compound and of
  Co3 in the other)

63
Transition Elements TheirCoordination Compounds

• Constitutional (Structural) Isomers
• Linkage Isomers
• Composition of the complex ion remains the same,
  but the attachment of the ligand donor atom
  changes
• Some ligands can bind to the metal ion through
  either of two donor atoms
• Ex. pentaamminenitrocobalt(III) chloride
• Co(NH3)5(NO2Cl2
• pentaamminenitritocobalt(III) chloride
• Co(NH3)5(ONOCl2
• Ex. Cyanate ion can attach via lone pair of
  electrons on
• the Oxygen atom (NCO)
• or the Nitrogen atom (isocyanato (OCN)

Other examples of alternate electron donor pairs
for Linkage IsomerS
64
Transition Elements TheirCoordination Compounds

• Constitutional (Structural) Isomers
• Stereo Isomers
• Compounds that have the same atomic connections
  but different spatial arrangements of the atoms
• Geometric Isomers (cis-trans isomers
  diastereomers)
• Atoms or groups of atoms arranged differently in
  space relative to the Central metal

65
Transition Elements TheirCoordination Compounds

• Constitutional (Structural) Isomers
• Stereo Isomers
• Optical Isomers (enantiomers)
• Occur when a molecule and its mirror image can
  not be superimposed
• Optical isomers have distinct physical properties
  like other types of isomers, with one exception
  the direction in which they rotate the plane of
  polarized light

Optical isomerism in an octahedral complex ion
Rotating structure I in the cis compound gives
structure III, which is not the same as structure
II, its mirror image, Image I Image III are
optical isomers
Rotating structure I in the trans compound gives
structure III,which is the same as structure II,
its mirror image, The trans compound does not
have any mirror images
66
Practice Problem

• Draw all stereo isomers for the following
• Pt(NH3)2Br2 Cr(en)33 (en
  H2NCH2CH2NH2)

Pt(II) complex is Square Planar Geometry Two
different monodentate ligands Geometric Isomers
Each isomer is superimposable on the mirror
image no optical isomerism
cis
trans
Ethylenediamine is a bidentate ligand The Cr3
has a coordination number of 6 and an octahedral
geometry, similar to Co3 The three bidendate
ions are identical ? No geometric isomerism This
complex ion has a nonsuperimposable mirror
image ? Optical Isomerism does occur
67
Transition Elements TheirCoordination Compounds

• Theoretical Basis for the Bonding and Properties
  of Complexes
• Questions
• How do Metal Ligand bonds form
• Why certain geometries are preferred
• Why are complexes often brightly colored
• Why are complexes often paramagnetic attracted
  to a magnetic field as a result of their electron
  pairs being unpaired

68
Transition Elements TheirCoordination Compounds

• Theoretical Basis for the Bonding and Properties
  of Complexes
• Application of Valence Bond Theory to Complex
  Ions
• In the formation of a complex ion, the filled
  ligand orbital overlaps the empty metal-ion
  orbital
• The Ligand (Lewis Base) donates the electron pair
  and the metal-ion (Lewis Acid) accepts it to form
  one of the covalent bonds of the complex ion
  (Lewis adduct)
• When one atom in a bond donates both electrons
  the bond is referred to as a coordinate covalent
  bond
• The number and type of metal-ion hybrid orbitals
  occupied by ligand lone pairs determine the
  geometry of the complex ion

69
Transition Elements TheirCoordination Compounds

• Application of Valence Bond Theory to Complex
  Ions
• Octahedral Complexes (six electron groups about
  central atom)
• Ex. Hexaamminechromium(III) ion CrNH3)63
• Six hybrid orbitals are needed to make the ion
• The six lowest energy orbitals of the Cr3 ion
• Two 3d, one 4s, three 4p
• mix and become six equivalent d2sp3 hybrid
  orbitals that point to the corners of an
  octahedron
• The six d2sp3 hybrid orbitals are filled with the
  six electron pairs from the six NH3 ligands

Note the lowest 6 energy levels for Cr3 involve
both n3 n4 sublevels The 3d orbitals are of
lower energy than the 4s and 4p orbitals The
hybrid designation, d2sp3, follows this order If
all the orbitals had the same n value, the
order would have been sp3d2
Paramagnetic Unpaired e-
70
Transition Elements TheirCoordination Compounds

• Application of Valence Bond Theory to Complex
  Ions
• Square Planar Complexes (four electron groups
  about central atom)
• Metal ions with a d8 configuration usually form
  square planar complexes
• In the Ni(CN)42- ion, the model proposes
• one 3d, one 4s, two 4p for Ni2
• to from four dsp2 hybrid orbitals pointing the
  corners of a square accepting one electron pair
  from each of the four CN- orbitals

Note the filling of the first 4 unhybridized 3d
orbitals after one 3d, one 4s and two 4p orbitals
combine to form the four dsp2 hybrid orbitals
Paramagnetic Unpaired e-
71
Transition Elements TheirCoordination Compounds

• Application of Valence Bond Theory to Complex
  Ions
• Tetrahedral Complexes (four electron groups about
  central atom)
• Metal ions that have a filled d sublevel, such as
  Zn2 Ar 3d10often form Tetrahedral complexes
• In the Zn(OH)42- ion, the model proposes the
  lowest available Zn2 orbitals
• one 4s, three 4p
• mix to become four sp3 hybrid orbitals that
  point to the corners of a tetrahedron, occupied
  by four lone pairs, one from each of the four OH-
  ligands

72
Transition Elements TheirCoordination Compounds

• Crystal Field Theory
• Valence Bond Theory pictures and rationalizes
  bonding and shape of molecules
• VB theory gives little insight into the colors of
  coordination compounds and can be ambiguous with
  regard to magnetic properites
• Crystal Field Theory explains color and magnetism
• Highlights the effects on the d-orbital
  energies of the metal ion as the ligands approach

73
Transition Elements TheirCoordination Compounds

• Crystal Field Theory
• What is Color?
• White light is electromagnetic radiation
  consisting of all wavelengths (?) in the
  visible range
• Objects appear colored in white light because
  they absorb certain wavelengths and reflect or
  transmit others
• Opaque objects reflect light
• Clear objects transmit light
• If the object absorbs all visible wavelengths, it
  appears black
• If the object reflects all visible wavelengths,
  it appears white

74
Transition Elements TheirCoordination Compounds

• Crystal Field Theory
• What is Color?
• Each color has a complimentary color
• An object has a particular color for two reasons
• It reflects (or transmits) light of that color or
• It absorbs light of the complimentary color
• Ex. If an object absorbs only red (compliment of
  green), it is interpreted as green

Colors with approximate wavelength
ranges Complimentary colors, such as red and
green,lie opposite each other
75
Transition Elements TheirCoordination Compounds

• Crystal Field Theory
• In CF Theory, the properties of complexes result
  from the splitting of d-orbital energies
• Split d-orbital energies arise from
  electrostatic interactions between the
  positively charged metal ion cation and the
  negative charge of the ligands
• The negative charge of the ligand is either
  partial as in a polar neutral ligand like NH3, or
  full, as in an anionic ligand like Cl-

76
Transition Elements TheirCoordination Compounds

• Crystal Field Theory
• The ligands approach the metal ion along the
  mutually perpendicular x, y, and z axes
  (octahedral orientation), minimizing the overall
  energy of the system
• B C Lobes of the dx2-y2 and dz2 orbitals lie
  directly in line with the approaching ligands and
  have stronger repulsions
• D, E, F lobes of the dxy, dxz, and dyz orbitals
  lie between the approaching ligands, so the
  repulsion are weaker

77
Transition Elements TheirCoordination Compounds

• Crystal Field Theory
• An energy diagram of the orbitals shows all five
  d orbitals are higher in energy in the forming
  complex than in the free metal ion, because of
  the repulsions from the approaching ligands
• Crystal Field Splitting Energy - The d orbital
  energies aresplit with the two dx2-y2 and dz2
  orbitals (eg orbital set) higher in energy than
  the dxy, dxz, and dyz orbitals (t2g orbital set)
• Strong-field ligands, such as CN- lead to larger
  splitting energy
• Weak-field ligands such as H2O lead to smaller
  splitting energy

Crystal Field Splitting Energy
Forming Complex
78
Transition Elements TheirCoordination Compounds

• Crystal Field Theory
• Explaining the Colors of Transition Metals
• Diversity in colors is determined by the energy
  difference (?) between the t2g and eg orbital
  sets in complex ions
• When the ions absorbs light in the visible range,
  electrons move from the lower energy t2g level to
  the higher eg level, i.e., they are excited and
  jump to a higher energy level
• ? E electron Ephoton hv hc/?
• The substance has a color because only certain
  wavelengths of the incoming white light are
  absorbed

79
Transition Elements TheirCoordination Compounds

• Crystal Field Theory
• Example Consider the Ti(H2O)63 ion Purple
  in aqueous solution
• Hydrated Ti3 is a d1 ion, with the d electron in
  one of the three lower energy t2g orbitals
• The energy difference (?A) between the t2g and eg
  orbitals corresponds to the energy of photons
  spanning the green and yellow range
• These colors are absorbed and the electron jumps
  to one of the eg orbitals
• Red, blue, and violet light are transmitted as
  purple

80
Transition Elements TheirCoordination Compounds

• Crystal Field Theory
• For a given ligand, the color depends on the
  oxidation state of the metal ion the number of
  d orbital electrons available
• A solution of V(H2O)62 ion is violet
• A solution of V(H2O)63 ion is yellow
• For a given metal, the color depends on the
  ligand
• Cr(NH3)63 (yellow-orange)
• Cr(NH3)52 (Purple)
• Even a single ligand is enough to change the color

81
Transition Elements TheirCoordination Compounds

• Crystal Field Theory
• Spectrochemical Series
• The Spectrochemical Series is a ranking of
  ligands with regard to their ability to split
  d-orbital energies
• For a given ligand, the color depends on the
  oxidation state of the metal ion
• For a given metal ion, the color depends on the
  ligand
• As the crystal field strength of the ligand
  increases, the splitting energy (?) increases
  (shorter wavelengths of light must be absorbed to
  excite the electrons

82
Practice Problem

• Rank the following ions in terms of the relative
  value of ? and of the energy of visible light
  absorbed
• Ti(H2O)63 Ti(NH3)63 Ti(CN)63
• Ans
• Oxidation State of Ti is 3 in all formulas
• From the spectrochemical series table, the ligand
  strength is in the order
• CN- gt NH3 gt H2O
• Relative size of ?, thus, the energy of light
  absorbed is
• Ti(CN)63 gt Ti(NH3)63 gt Ti(H2O)63

83
Transition Elements TheirCoordination Compounds

• Explaining the Magnetic Properties of Transition
  Metal Complexes
• The splitting of energy levels influence magnetic
  properties
• Affects the number of unpaired electrons in the
  metal ion d orbitals
• According to Hunds rules, electrons occupy
  orbitals one at a time as long as orbitals of
  equal energy are available
• When all lower energy orbitals are half-filled
  (all ½ spin state), the next electron can
• Enter a half-filled orbital and pair up (with a
  ½ spin state electron) by overcoming a repulsive
  pairing energy (Epairing)
• or
• Enter an empty, higher energy orbital by
  overcoming the crystal field splitting energy (?)
• The relative sizes of Epairing and (?) determine
  the occupancy of the d orbitals

84
Transition Elements TheirCoordination Compounds

• Crystal Field Theory
• Explanation of Magnetic Properties
• The occupancy of d orbitals, in turn,
  determines the number of unpaired electrons,
  thus, the paramagnetic behavior of the ion
• Ex. Mn2 ion (Ar 3d5) has 5 unpaired
  electrons in 3d orbitals of equal energy
• In an octahedral field of ligands, the orbital
  energies split
• The orbital occupancy is affected in two ways
• Weak-Field ligands (low ?) and High-Spin
  complexes
• Strong-Field ligands (high ?) and Low-Spin
  complexes
• (from spectrochemical series)

85
Transition Elements TheirCoordination Compounds

• Crystal Field Theory
• Explanation of Magnetic Properties
• Weak-Field ligands and High-Spin complexes
• Ex. Mn(H2O)62 Mn2 (Ar 3d5)
• A weak-field ligand, such as H2O, has a small
  crystal field splitting energy (?)
• It takes less energy for d electrons to move
  tothe eg set (remaining unpaired) rather
  thanpairing up in the t2g set with its
  higherrepulsive pairing energy (Epairing)
• Thus, the number of unpaired electrons in
  aweak-field ligand complex is the same as inthe
  free ion
• Weak-Field Ligands create high-spin
  complexes,those with a maximum of unpaired
  electrons
• Generally Paramagnetic

86
Transition Elements TheirCoordination Compounds

• Crystal Field Theory
• Explanation of Magnetic Properties
• Strong-Field Ligands and Low-Spin Complexes
• Ex. Mn(CN)64-
• Strong-Field Ligands, such CN-, cause large
  crystal field splitting of the d-orbital
  energies, i.e., higher (?)
• (?) is larger than (Epairing)
• Thus, it takes less energy to pair up in the
  t2g set than would be required to move up to
  the eg set