Chapter 23 The Transition Elements and Their Coordination Compounds

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Chapter 23 The Transition Elements and Their Coordination Compounds Powered By Docstoc
					           Chapter 23
The Transition Elements and Their
    Coordination Compounds
The Transition Elements (d block) and
Inner Transition Elements (f block)
Zinc Fingers
Hemoglobin
      Electron Configuration
On your white board draw the electron
configuration for the following:
 —K

 — Mn

 — Pt

 — Cd

 — Mn+2

 — Fe
      +3
   Horizontal Trends in Key Atomic
   Properties of the Period 4 Elements

1. What trends
do we see
across the
periodic table?

2. What trends
to we see
vertically?
Aqueous Oxo-anions of Transition
Elements
                             One of the most
                             characteristic chemical
                             properties of these
                             elements is the
                             occurrence of multiple
                             oxidation states.
Mn(II)    Mn(VI)   Mn(VII)




                                             Mn(VII)
                                  Cr(VI)
                      V(V)
Transition Metal Complexes
 (Coordination Complexes)
                       Take a
                       moment and
                       draw Cisplatin
                       and NAMI-A on
                       your white
                       board
Formulas of Coordination Compounds

1.   Cation then anion
2.   Total charges must balance to zero
3.   Complex ion in brackets


              K2[Co(NH3)2Cl4]

              [Co(NH3)4Cl2]Cl
Complex Ion
Species where transition metal ion is
 surrounded by a certain number of
 ligands.

 Transition metal ion:   Lewis acid
 Ligands:                Lewis bases

                  Co(NH3)63+
                  Pt(NH3)3Br+
Coordination Compounds
Consist of a complex ion and necessary counter ions
      [Co(NH3)5Cl]Cl2

Complex ion:     [Co(NH3)5Cl]2+
                      Co3+ +      5 NH3    + Cl-
                   = 1(3+) +       5 (0)    + 1(1-)
                   = 2+

Counter ions:    2 Cl-
Structures of Coordination Complexes


  Coordination Number - the number of ligand
  atoms that are bonded directly to the central
  metal ion. The coordination number is specific
  for a given metal ion in a particular oxidation
  state and compound.
  Geometry - the geometry (shape) of a
  complex ion depends on the coordination
  number and nature of the metal ion.

  Donor atoms per ligand - molecules and/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.
Components of a Coordination Compound




 models         wedge        chemical
               diagrams      formulas
Ligands
Molecule or ion having a lone electron pair that can
 be used to form a bond to a metal ion
 (Lewis base).

coordinate covalent bond: metal-ligand bond

  monodentate: one bond to metal ion
  bidentate:   two bond to metal ion
  polydentate: more than two bonds to a metal
               ion possible
Ligands
Important types of Isomerism in Coordination
Compounds

                                    ISOMERS
           Same chemical formula, but different properties

Constitutional (structural) isomers                  Stereoisomers
    Atoms connected differently               Different spatial arrangement

 Coordination        Linkage            Geometric (cis-       Optical isomers
   isomers           isomers             trans) isomers       (enantiomers)
                                        (diastereomers)
  Ligand and      Different donor                           Nonsuperimposable
  counter-ion          atom                 Different         mirror images
   exchange                            arrangement around
                                            metal ion
Let’s Practice: Isomers
Constitutional Isomers:
Draw all the isomers of hexane (C6H14)



Geometric Isomers:
Draw the cis and trans structure for C2H2Cl2

Stereoisomers:
Use the model kits to create a compound with
  four different balls around a central carbon
  atoms.
Linkage Isomers
Geometric (cis-trans) Isomerism
             Let’s Draw again!
Draw all geometric isomers for the following:

1. [Pt(NH3)2Br2]
Crystal Field Theory
Focus:    energies of the d orbitals

Assumptions
1.   Ligands: negative point charges
2.   Metal-ligand bonding: entirely ionic

strong-field: large splitting of d orbitals
weak-field: small splitting of d orbitals

  Provides little insight about metal-ligand
  bonding, but explains color and magnetism!
Which will be higher in
      energy?
Splitting of d-orbital energies by an
octahedral field of ligands.




              D is the splitting energy
Does this give us any new insights into
   why these complexes have such
            wonderful colors?

In your groups with a white board, use
 this new idea to suggest a reason for
  color in these beautiful compounds.
High spin   Low spin
High-spin and Low-spin Complex Ions of Mn2+
Orbital occupancy for high- and low-spin
complexes of d4 through d7 metal ions.


    high spin:   low spin:   high spin:   low spin:
    weak-field    strong-    weak-field    strong-
      ligand        field      ligand        field
                   ligand                   ligand
Problem Solving
Rank the ions [Ti(H2O)6]3+, [Ti(NH3)6]3+, and
[Ti(CN)6]3- in terms of the relative value of D
and of the energy of visible light absorbed.
Splitting of d-orbital energies by a
tetrahedral field and a square planar field
of ligands.




tetrahedral




                            square planar
Hemoglobin




 http://www.umass.edu/molvis/tutorials/hemoglobin/index.htm
Iron Porphyrin




        Electron Configuration?
        Coordination Number?
        Shape?
        Ligands?
A Closer look at Iron

 Iron (II) forms an essential complex in
 hemoglobin. For each of the two octahedral
 complex ions [Fe(H2O)6]2+ and [Fe(CN)6]4-, draw
 an orbital splitting diagram, predict the number
 of unpaired electrons, and identify the ion as
 low or high spin.

				
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posted:11/25/2011
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