Chapter 24 Transition Metals and Coordination Compounds

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Chapter 24Transition Metals and Coordination
Compounds
Chemistry A Molecular Approach, 1st Ed.Nivaldo
Tro
Roy Kennedy Massachusetts Bay Community
College Wellesley Hills, MA
2007, Prentice Hall
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Gemstones

• the colors of rubies and emeralds are both due to
  the presence of Cr3 ions the difference lies
  in the crystal hosting the ion

Some Al3 ions in Be3Al2(SiO3)6 are replaced by
Cr3
Some Al3 ions in Al2O3 are replaced by Cr3
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Properties and Electron Configuration of
Transition Metals

• the properties of the transition metals are
  similar to each other
• and very different to the properties of the main
  group metals
• high melting points, high densities, moderate to
  very hard, and very good electrical conductors
• in general, the transition metals have two
  valence electrons we are filling the d orbitals
  in the shell below the valence
• Group 1B and some others have 1 valence electron
  due to promotion of an electron into the d
  sublevel to fill it
• form ions by losing the ns electrons first, then
  the (n 1)d

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Atomic Size

• the atomic radii of all the transition metals are
  very similar
• small increase in size down a column

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Ionization Energy

• the first ionization energy of the transition
  metals slowly increases across a series
• third transition series slightly higher 1st IE
• trend opposite to main group elements

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Electronegativity

• the electronegativity of the transition metals
  slowly increases across a series
• except for last element in the series
• electronegativity slightly increases down the
  column
• trend opposite to main group elements

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Oxidation States

• often exhibit multiple oxidation states
• vary by 1
• highest oxidation state is group number for 3B to
  7B

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Coordination Compounds

• when a complex ion combines with counterions to
  make a neutral compound it is called a
  coordination compound
• the primary valence is the oxidation number of
  the metal
• the secondary valence is the number of ligands
  bonded to the metal
• coordination number
• coordination number range from 2 to 12, with the
  most common being 6 and 4
• CoCl3?6H2O Co(H2O)6Cl3

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Coordination Compound
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Complex Ion Formation

• complex ion formation is a type of Lewis
  acid-base reaction
• a bond that forms when the pair of electrons is
  donated by one atom is called a coordinate
  covalent bond

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Ligands with Extra Teeth

• some ligands can form more than one coordinate
  covalent bond with the metal atom
• lone pairs on different atoms that are separate
  enough so that both can reach the metal
• chelate is a complex ion containing a
  multidentate ligand
• ligand is called the chelating agent

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EDTAa Polydentate Ligand
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Complex Ions with Polydentate Ligands
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Geometries in Complex Ions
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Common Ligands
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phenanthroline
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• Fe(en)(NH3)4Cl3
• Fe is 3
• 3 moles of AgCl would form

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Common Metals found in Anionic Complex Ions
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Naming Coordination Compounds

• List ligand names in alphabetical order
• name each ligand alphabetically, adding a prefix
  in front of each ligand to indicate the number
  found in the complex ion
• follow with the name of the metal cation,
  indicate the oxidation number with Roman
  numerals.
• If the complex is an anion, the suffix ate is
  added to the metal name.

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Ligands Names

• anions ending with ate or ide change to o as
  in nitrate to nitrato or cyanide to cyano
• anions with ite change to e
• molecules uses common name except for
• water changes to aqua
• ammonia to ammine
• CO to carbonyl
• multiple simple ligands are prefixed with di,
  tri, tetra, penta, or hexa.
• Complex ligands are prefixed with bis, tris,
  tetrakis, pentakis, or hexakis.

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Practice

• K2Ni(CN)4
• NaCr(C2O4)2(H2O)2
• Ru(phen)4Cl3

Tetracyanonicklate(II) potassium
Diaquobis(oxylato)chromate(III) sodium
Tetrakis(phenanthroline)ruthunium(III) chloride
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• Practice
• aquachlorobis(ethylenediamine) cobalt(III)
  chloride
• Pentacarbonyliron(0)
• Triaminechloroetheylenediamenecobalt(III)

Co(H2O)(Cl)(en)22Cl
Fe(CO)5
Co(NH3)3(Cl)(en)2
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Isomers

• Structural isomers are molecules that have the
  same number and type of atoms, but they are
  attached in a different order
• Stereoisomers are molecules that have the same
  number and type of atoms, and that are attached
  in the same order, but the atoms or groups of
  atoms point in a different spatial direction

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Linkage Isomers
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Geometric Isomers

• geometric isomers are stereoisomers that differ
  in the spatial orientation of ligands

• cis-trans isomerism in octahedral complexes MA4B2

• fac-mer isomerism in octahedral complexes MA3B3

• cis-trans isomerism in square-planar complexes
  MA2B2

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Ex. 24.5 Draw the structures and label the type
for all isomers of Co(en)2Cl2

• the ethylenediamine ligand (en H2NCH2CH2NH2) is
  bidentate
• each Cl ligand is monodentate
• octahedral
• MA4B2

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Optical Isomers
Co(en)33

• optical isomers are stereoisomers that are
  nonsuperimposable mirror images of each other

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Ex 24.7 Determine if the cis-trans isomers of
Co(en)2Cl2 are optically active

• draw the mirror image of the given isomer and
  check to see if they are superimposable

trans isomer identical to its mirror image
cis isomer mirror image is nonsuperimposable
no optical isomerism
optical isomers
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Bonding in Coordination CompoundsValence Bond
Theory

• bonding takes place when the filled atomic
  orbital on the ligand overlaps an empty atomic
  orbital on the metal ion
• explain geometries well, but doesnt explain
  color or magnetic properties

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Bonding in Coordination CompoundsCrystal Field
Theory

• bonds form due to the attraction of the electrons
  on the ligand for the charge on the metal cation
• electrons on the ligands repel electrons in the
  unhybridized d orbitals of the metal ion
• the result is the energies of orbitals the d
  sublevel are split
• the difference in energy depends on the complex
  and kinds of ligands
• crystal field splitting energy
• strong field splitting and weak field splitting

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Splitting of d Orbital Energies due to Ligands in
a Octahedral Complex
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Strong and Weak Field Splitting
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How we see color

• If we see black, the material absorbs all color
• If we see white, the material reflect all color

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Complex Ion Color

• Absorbs all colors-but- the one you see or
• Reflects most colors but absorbs the the
  complimentary

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Complex Ion Color and Crystal Field Strength

• the colors of complex ions are due to electronic
  transitions between the split d sublevel orbitals
• the wavelength of maximum absorbance can be used
  to determine the size of the energy gap between
  the split d sublevel orbitals
• Ephoton hn hc/l D

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Ligand and Crystal Field Strength

• the strength of the crystal field depends in
  large part on the ligands
• strong field ligands include CN- gt NO2- gt en gt
  NH3
• weak field ligands include
• H2O gt OH- gt F- gt Cl- gt Br- gt I-
• crystal field strength increases as the charge on
  the metal cation increases

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Magnetic Properties and Crystal Field Strength

• the electron configuration of the metal ion with
  split d orbitals depends on the strength of the
  crystal field
• the 4th and 5th electrons will go into the higher
  energy dx2-y2 and dz2 if the field is weak and
  the energy gap is small leading to unpaired
  electrons and a paramagnetic complex
• the 4th thru 6th electrons will pair the
  electrons in the dxy, dyz and dxz if the field is
  strong and the energy gap is large leading to
  paired electrons and a diamagnetic complex

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Low Spin High Spin Complexes
only electron configurations d4, d5, d6, or d7
can have low or high spin
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Tetrahedral Geometry andCrystal Field Splitting

• because the ligand approach interacts more
  strongly with the planar orbitals in the
  tetrahedral geometry, their energies are raised
• most high-spin complexes

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Square Planar Geometry andCrystal Field Splitting

• d8 metals
• the most complex splitting pattern
• most are low-spin complexes

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Applications of Coordination Compounds

• extraction of metals from ores
• silver and gold as cyanide complexes
• nickel as Ni(CO)4(g)
• use of chelating agents in heavy metal poisoning
• EDTA for Pb poisoning
• chemical analysis
• qualitative analysis for metal ions
• blue CoSCN
• red FeSCN2

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Applications of Coordination Compounds

• commercial coloring agents
• prussian blue mixture of hexacyanoFe(II) and
  Fe(III)
• inks, blueprinting, cosmetics, paints
• biomolecules
• porphyrin ring
• cytochrome C
• hemoglobin
• chlorphyll

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Applications of Coordination Compounds

• carbonic anhydrase
• catalyzes the reaction between water and CO2
• contains tetrahedrally complexed Zn2

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Applications of Coordination Compounds

• Drugs and Therapeutic Agents
• cisplatin
• anticancer drug