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COORDINATION COMPOUNDS

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COORDINATION COMPOUNDS Powered By Docstoc
					  Chapter 20

 Transition Metals and
Coordination Chemistry
 COORDINATION COMPOUNDS
-- Lewis Acid - Base reactions:
            Base – electron pair donor
            Acid - electron pair acceptor
-- Coordinate covalent bonds
-- ligands, Lewis bases
-- Complex ions called “Metal Complexes”
       ALFRED WERNER’S
     COORDINATION THEORY
-- Oxidation number of central atom
-- Coordination number
-- Coordination sphere (containing metal ion)
     - anions
     - cations
     - neutral
-- Geometry
     - look at hybridization shapes
-- Ligands
             Formulas and Name of Some Common Ligands
               Formula                 Name
               H2O                     aqua
               NH3                     ammine
               CO                      carbonyl
               NO                      nitrosyl
               H2NC2H4NH2              ethylenediamine
               OH-                     hydroxo
               O2-                     oxo
               F-                      fluoro
               Cl-                     chloro
               Br-                     bromo
               I-                      iodo
               CN-                     cyano
               -NCS-                   isothiocyanato*
               -SCN-                   thiocyanato*
               SO42-                   sulfato
               SO32-                   sulfito
               NO3-                    nitrato*
               -NO2-                   nitro*
               -ONO-                   nitrito*
               CO32-                   carbonate
*In these ligands two forms are known; they differ in the atom that donates the electron pair to
the metal ion.
Various
coordination
geometries
                          Nomenclature of Coordination Compounds
1.The cation is named first in ionic compounds, then the anion.
2.Nonionic compounds are given a one-word name.
3.The following rules pertain to the names of ligands.
     a. The ligands are named first and the central atom last.
     b. Ligands are named in alphabetical order by their root name.
     c. Neutral ligands are named the same as the molecule, except for a few such as
         H2O (aqua) and NH3 (ammine), which have special names.
     d. Anionic ligands are named by adding –o to the stem of the usual name, such as
         chloro for Cl- and sulfato for SO42-.
     e. The name of each ligand is preceded by a Latin prefix (di-, tri- tetra-, penta,
         hexa- etc.) if more than one of that ligand Is bonded to the cetnral atom. For
         example, the ligands in PtCl42- are named tetrachloro, and the ligands in
         Co(NH3)4Cl2+ are named tetraamminedichloro.
         If the ligand is polydentate, as in ethylenediamine, the number of ligands
         bonded to the central atom is indicated by the corresponding Greek prefixes
         (bis-, tris-, tetrakis-, pentakis-, hexakis-, etc.). For example, the ligands in
         Co(en)33+ are named trisethylenediamine. A Greek prefix is also used when a
         Latin prefix forms a part of the name of the ligand, as in triethylamine,
         N(CH3)3. In this case, the ligand name is enclosed in parentheses. For
         example, the ligands in [Co(N(CH3)3)4]2+ are named tetrakis(triethylamine).
4,   For a cationic complex ion or a nonionic compound, the central atom is given its
     ordinary name followed by its oxidation number n Roman numerals, enclosed in
     parentheses. For example, [Cr(H2O)5Cl]2+ is named
     pentaaquachlorochromium(III) ion, and [Cr(NH3)3Cl3] is name
     triamminetrichlorochromium (III).
5.   For anionic complex ions, the suffix –ate is added to the name of the central atom,
     followed by the oxidation number in Roman numerals, enclosed in parentheses.
     For example, [Cr(CN)6]3- is name hexacyanochromate (III) ion.
Name the following complex ions.
   a. Ru(NH3)5Cl2+
   b. Fe(CN)64-
   c. Mn(NH2CH2CH2NH2)32+
   d. Co(NH3)5NO22+

Name the following coordination compounds.
   a. [Co(NH3)6]Cl2
   b. [Co(H2O)6]I3
   c. K2 [PtCl4]
   d. K4[PtCl6]
Give the formulas for the following.
     a. Hexakispyridinecobalt(III)chloride
     b. Pentaammineiodochromium(III) iodide
     c. Trisethylenediamminenickel(II)bromide
     d. Potassium tetracyanonickelate(II)
     e. Tetraamminedichloroplatinum(IV)
                      tetrachloroplatinate(II)
Draw geometrical isomers of each of the
following complex ions.
     a. [CO(C2O4)2(H2O2]-
     b. [Pt(NH3)4I2]2+
     c. [Ir(NH3)3Cl3]
     d. [Cr(en(NH3)2I2]+
Amino acids can act as ligand toward transition
metal ions. The simplest amino acid is glycine
(NH2CH2CO2H). Draw a structure of the glycinate
anion (NH2CH2CO2-) acting as a bidentate ligand.
Draw the structure isomers of the square planar
complex Cu(NH2CH2CO2)2.

BAL is a chelating agent used in treating heavy-
metal poisoning. It acts as a bidentate ligand. What
types of linkage isomers are possible when Bal
coordinates to a metal ion?
Geometrical Isomers of [Co(NH3)4Cl2]+
Geometrical isomers of [pt(NH3)2Cl2]
Mirror images of cis-[Co(en)2Cl2]+ and trans-[Co(en)2Cl2]+
    COORDINATION
 COMPOUND REACTIONS
Oxidation – Reduction
     Outer sphere: coordination sphere
     and ligands do not change.
     Inner sphere: one or more
     coordination sphere changes.

Substitution Reactions (Displacement)

Ligand reactions
 COORDINATE COVALENT
 BONDS AND GEOMETRY
          Valence Bond Theory
                 versus
          Crystal Field Theory
Valence Bond             hybridization
Octahedral               d2sp3
Tetrahedral              sp3
Square planar            dsp2
“low spin” and “high spin” complexes
The 6 ligands in an octahedral crystal field
Formation of   d2sp3   orbitals
Draw the d-orbital splitting diagrams for the
octahedral complex ions of each of the
following.
     a. Fe2+ (high and low spin)
     b. Fe3+ (high spin)
     c. Ni2+
     d. Zn 2+
     e. Co2+ (high and low spin)

How many unpaired electrons are in the
following complex ions?
     a. Ru(NH3)62+ (low-spin case)
     b. Fe(CN)63- (low-spin case)
     c. Ni(H2O)62+
     d. V(en)33-
     e. CoCl42-
The 4 ligands in a tetrahedral crystal field
Tetrahedral crystal field splitting energy
  The d
  orbital
  energy
   level
 diagram
  for an
octahedral
 complex
Free Co
orbitals
   The d
  energy
 diagrams
for square,
  planar,
and linear
complexes
Spectra of emerald and ruby
Absorption and emission of light
   by Cr (III) complex ions
                    Spectrochemical Series of Ligands

              Wavelength in nm                    Crystal Field
              of Peak in Spectrum                 Splitting Energy
Ligand        of Co(NH3)4X* (nm)                  for Co(NH3)5X (kJ/mol)
CO
CN-           440                                 272
-NO2-         458                                 261
en
-NC-                                                             Large 
NH3           475                                 252
-NCS-         496                                 241
OH2           490                                 244              Pairing
C2O42-
                                                                   Energy
-ONO-         491                                 244
OH    -       503                                 238
-ONO2   -     500                                 239
    -
F
Cl-
              510
              533
                                                  235
                                                  224           Small 
-SCN-
S2-
Br-           550                                 217
I -           580                                 206
*This wavelength is that at which there is a maximum absorption of light in the
spectrum of the Cobalt(III) complex ion.
The complex ion NiCl42- has two unpaired
electrons, while Ni(CN)42- is diamagnetic.
Propose structures for these two complex ions.




Tetrahedral complexes of Co2+ are quite
common. Use a d-orbital splitting diagram to
rationalize the stability of Co2+ tetrahedral
complex ions.
The compound Ni(H2O)6Cl2 is green, while
Ni(NH3)6Cl2 is purple. Predict the predominant
color of light absorbed by each compound. Which
compound absorbs light with the shorter
wavelength? Predict in which compound is
greater and whether H2O or NH3 is a stronger field
ligand. Do your conclusions agree with the
spectrochemical series?
The complex ion Fe(CN)63- is paramagnetic with one
unpaired electron. The complex ion Fe(SCN)63- has
five unpaired electrons. Where does SCN- lie in the
spectrochemical series relative to CN-?

				
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