Coordination Nomenclature Coordination Chem

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Coordination Nomenclature Coordination Chem Powered By Docstoc
					     Nomenclature &
    Coordination Chem

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    Lewis Acid - Lewis Base Chemistry

    Lewis Acid : e- acceptor
     (metals are good e- acceptor)
    Lewis Base : e- donor
     (Ligands with lone pair electrons)

    Ligands, atoms or cluster of atoms with
    lone pair electrons available to donate
    Complexing Agent: H2O, NH3, Cl- CN-

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    Metal possesses open orbitals to accept e- pair.
    M with empty d- orbitals
    Ligand with e- pair
    Combine to form LA-LB (Compound)
      In general, the complex is more stable than the separated compound.
    Complex - Metal ion bonded to a number of ligands

               M           M

               M           M

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       Complex -
    Metal- Ligand compounds
     [MLn] i.e., [Ag(NH3)2]+ or [Co(NH3)6] Cl3
    [ ] denotes atoms bonded to each other
    through covalent bonds. These atoms are
    contained in the coordination sphere.

    Coordinated sphere is the directly bonded to each other.
    Counter ions are outside bracket, and are not part of the coordinate
    A coordinated compound behaves like an electrolyte in water: the
    complex ion and counter separates from each other. But the
    complex ion behaves like a polyatomic ion: the ligands and central
    metal ion remain attached.
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                                   Coordination Number
    CN - Number of ligand atoms bonded directly to the central metal ion.
     Specific for given metal ion in particular Oxidation #.
     i.e., [Co(NH3)6]+      CN = 6           Ligand # = 6
            [Ag(NH3)2]+     CN = 2           Ligand # = 2
            [Co(en)3]+      CN = 6           Ligand # = 3
    Geometry of Complex is related to CN.
     CN = 2                  Linear                        CN= 4        Tetrahedral (d10)
                                                                                      Sq Planar (d8)

    CN = 5                   Trigonal bipyramidal                                                          Br


                                   Square Pyramide                                                                F

                                                           CN = 6       Octahedral



                                          F            F


                                      F            F                                                   F


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             Coordinated Complexes and
               Coordination Number
    Coord     Shape                                                             Example
      2       Linear                                                       [CuCl2]-, [Ag(NH3)2]+, [AuCl2]-

      4       Square Planar           F
                                                                           [Ni(CN)4] 2-, [PdCl4]2-
                                                  Br                       [Pt(NH3)4] 2+, [Cu(NH3)4] 2+


      4       Tetrahedral                                                   [Cu(CN)4] 3-, [Zn(NH3)4]2+
                                                                           [CdCl4] 2-, [MnCl4] 2-

      6       Octahedral                                                   [Cu(H2O)6] 3+, [V(CN)6] 4-,

                                                                           [Cu(NH3)4Cl2] +, [Co(en)3] 3+





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    Consider [Ag(NH3)2]+
    Ligand (contains the donor atom, directly bonded to metal)
      :NH3 - ligand occupy one site in coordinate sphere
    examples (Monodentate)
      N3- , X-, CN- , OH-, NH3 , pyridine, H2O
    Polydentate ligand - known as chelating agents -
     ligand which has several donor sites that can multi-bond
     (coordinate) metal simultaneously (chelates)
      i.e. en, oxalate, 1.10 phenanthroline, carbonate, bipyridine
      [EDTA]4- or (ethylenediaminetetraacetate), phenylpyridine

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     Example of Typical mono-, bi- and poly dentate Ligands

    Name of Neutral and Anionic Ligands:
    Neutral:            Anionic
    Aqua H2O             Fluoro Fl-
    Amine NH3            Chloro Cl-
    Nitrosyl NO          Bromo Br-
    Carbonyl CO          Iodo I-
                         Hydroxo OH-
                         Cyano CN-

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    Chelating Ligands have two or more donor atoms that
      simultaneously coordinate to a single metal ion.
    Polydentate - (Many toothed - ligand)
    Chelating agent (Claw)
    Sequestering agent - sequester - to set apart or separate

    en   ethylenediamine (shown) - two toothed ligand:
      i.e., [Co(en)3]3+ [Pt(en)2]2+
    EDTA ethylenediaminetetraacetate
      (picture) hexadentate
      EDTA is the antidote for
      heavy metal poisoning

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     Chelating agents in Living system

     Seven of 24 elements necessary for life,
     based on ability to formed complexes
      V, Cr, Mn, Fe, Co, Cu, Zn
     Fe - hemoglobin, chlorophyll (Mg)
     Co - Vitamin B

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                        Chelating effect
     A complex containing chelate ligands is more
     stable than that from a monodentate ligand.

     Kf, larger for chelating complex.
     Ni(H2O)62+ + 6NH3  Ni(NH3)6 + 6H2O                       kf = 4•108
     Ni(H2O)62+ + 3en  Ni(en)3 + 6H2O                         kf = 2•1018

     Driven by Entropy:
     Note that in the above reaction, the entropy increases via the increase
     of number of moles in the overall reaction. In reaction (1) there are 7
     moles of reactant changing to seven moles of product but in reaction
     (2) there are 4 moles of reactant changing to 7 moles of product, Kf is
     much larger for reaction (2).

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     Biological Coordinating Complexes

     Oxymyoglobin       Ferrichrome

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     Cation - Anion: Salts: name cation before anions i.e., [Co(HN3)5Cl]Br2,
      we name [Co(HN3)5Cl] complex ion before bromides counter ions .

     Complex: Within complex ion, the ligands are named in alphabetical
      order before the metal i.e., tetraaminechlorocobalt(II), note that tetra is an
      indication of the number of NH3 group, and not considered in the
      alphabetizing of the ligand.

     Ligand: Anionic ligands end in -o and neutral ligands are name based
      on their molecular name (excepts are aqua H2O, amine: NH3)
       Greek prefixes are used to indicate number of ligands, di-, tri-, tetra-, penta-,
       hexa-. Exception occurs when ligand already has Greek prefix in its name, The
       prefixes bis-, tris-, tetrakis-, pentakis, & hexakis. are used instead.
       i.e., Ir(bpy)3 trisbipyridineiridium (III) bipyridine already has bi in its name.

     If the complex is an anion, then its name ends with suffix -ate.
     Further more, oxidation state of the metal is given in roman numerals in
      parenthesis at the end of the name.

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      1. The cation is written before the anion.
      2. The charge of the cation(s) is balanced by the charge of the anion(s).
      3. For the complex ion, neutral ligands are written before anionic
           ligands (negative charge), and the whole ion is placed in brackets.

     Procedure Outline:
      1. The cation is named before the anion.
      2. Within the complex ion, the ligands are named, in alphabetical order.
      3. Neutral ligands generally have the molecule name.
           Anionic ligands drop the -ide and add -o after the root name.
      4. Numerical prefixes denote the number of a particular ligand.
      5. Oxidation state of metal ion is in Roman numeral in parenthesis.
      6. For anionic complex, the end of the metal name is replaced by -ate.

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       Example: Naming from Formula
     Name from formula
     a) K3[Au(CN)4]
       Potassium Tetracyanoaurate(I)
     d) K[Co(C2O4)2(NH3)2]
      Potassium diaminedioxaloCobaltate(I)
     f) [Cr(en)2F2]NO3
      Bis(ethylenediamine)difluorochromium(III) nitrate

     Naming anionic metals
      Iron: Ferrate               Copper: Cuprate
      Lead: Plumbate              Silver: Argentate
      Gold: Aurate                Tin:    Stannate

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         Example: Formula from Name
     Name from formula
     a) Hexaamminechromium(III) nitrate
          [Cr(NH3)4] (NO3)3
     d) dichlorobis(ethylenediamine)platinum(IV) bromide
     f) bis(ethylenediamine)zinc(II) tetraiodomercurate(II)

     More anionic metals
     Osmium:    Osmate             Cobalt:      Cobaltate
     Amtimony: Antimonate          Rhenium:     Rhenate
     Platinum: Platinate           Rhodium:     Rhodate

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     Coordinate Number (CN):
      Number of donor atoms bonded to metal
      2- coordinate - linear
      4 - coordinate tetrahedral and square planar
        ML4 , Pt(II) is always CN = 4
      6- octahedral
        ML6, Cr(III) and Co(III) CN = 6

      CN influence by
      Size of metal ion
         Small metal /large ligand - Low coordinate number
      Surrounding ligand
         Large metal / small ligand - High coordination number
         i.e., FeF63- and FeCl4- only

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