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Coordination Compounds

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					        INORGANIC CHEMISTRY


                                                     Coordination Compounds
                                      -
        A Lewis base (e donor) donates a pair of electrons to a Lewis acid (e- acceptor) forming a
        co-ordinate covalent bond.
                                                                                      1s0 1s 11s11s 1
                                                                                      H+ H H H
                                                                                                             Hydrogen ion has a vacant 1s orbital.
                                                                  +
     H                                           H                                                           Nitrogen has a full sp 3 orbital.
                                                                                                             A co-ordinate covalent bond is formed
 H        N:         +       H+              H        N       H                   N                          when nitrogen donates its lone e - pair
     H                                           H                                    sp3 orbitals           to hydrogen's empty 1s orbital.
ammonia
                                            ammonium ion
                                                                                                           2pz
                                                                                           sp2 orbitals
    H                        F                       H                    F                                      Boron has a vacant 2p z orbital.
H        N:      +       B       F               H        N       B           F        B                         Nitrogen has a full sp 3 orbital.
  H                                                                                                              A co-ordinate covalent bond is formed
                             F                       H                    F
ammonia                                                                                N                         when nitrogen donates its lone e - pair
                                                                                                                 to boron's empty 2p z orbital.
                                                                                            sp3 orbitals

        Ammonia is the Lewis base (electron donor). H+ and BF3 are Lewis acids (electron acceptors).
        Similarly, transition metals and their cations are Lewis acids. They have vacant orbitals that can
        accept electron pairs from donor atoms (Lewis bases) forming coordination compounds or
        complexes. Some examples are shown in the following table.
        Lewis Acid        Lewis Base     Complex          Dissociation Constants
        Cr+3     +        6H2O       [Cr(OH2)6]+3             -------------
        Co+3         +               6NH3          [Co(NH3)6]+3                       2.2  10-34
        Ni+2         +               4CN-          [Ni(CN)4]-2                        1.0  10-31
        Fe           +               5CO           [Fe(CO)5]                          -------------
        Ag   +
                     +               2NH3          [Ag(NH3)2]       +
                                                                                        6.3  10-8

        Lewis bases (anions or molecules) bonded to the central Lewis acid are called ligands (Latin =
        tie or bind). Charged coordination complexes also have counter ions associated with them to
        satisfy electroneutrality. For example, in [Ag(NH3)2]+NO3-, a nitrate anion is the counter ion.
        Counter ions are ionically bonded. When dissolved in water, the NO3- ion separates from the
        complex, but the two NH3 ligands remain firmly bound to the Ag+ ion by covalent bonds.
        The number of atoms bonded to the central ion/atom of a coordination complex is referred to as
        its coordination number. The coordination number of [Ag(NH3)2]+NO3- is two. The coordination
        number of [Fe(CO)5] is five. Coordination complexes occur with coordination numbers of 2
        through 12, however, coordination numbers of 2, 4 and 6 are most common.
        Complexes such as [Fe(CO)5] are usually insoluble in water since they are covalent compounds
        in which any dipoles cancel. Complexes such as [Ag(NH3)2]+NO3- are generally very soluble in
        water since they are made up of cations, e.g., [Ag(NH3)2]+ and anions, e.g., NO3-.
        Importance of Coordination Complexes:
        Many biologically important substances are 'd'-transition metal coordination compounds that are
        made up of large organic molecules bound to the metal via coordinate covalent bonds, e.g.,
         hemoglobin (blood protein) is a coordination complex involving Fe.
         vitamin B-12 is a cobalt complex (cyanocobalamin)
         phthalocyaine blue is a Cu complex dye used for blue jeans and ink




        Coordination Complexes                                                                                                                1
INORGANIC CHEMISTRY


    complexing agents are used for water softening (Ca, Mg, Fe removal with EDTA)
    an antidote for some metal poisoning (BAL) forms complexes with As, Hg, and Cr.
    Fe-carbonyls are anti-knock gasoline additives
Structure of Coordination Compounds:
Structures are determined by the coordination number and VSEPR. Lone pairs of e-'s in
d-orbitals have minimal influence on geometry because they are not in the outer shell.
In the following table, “Co #” refers to coordination number of the central atom or ion.

                           Geometries of Various Coordination Numbers
    Co#                    Geometry                      Hybridization   Hybridization        Examples
                                                         (nonmetals)      (transition    (transition metals)
                                                                            metals)

    2                                                     sp (BeH2)           sp           [Ag(NH3)2]+
                           linear                                                           [Cu(CN)2]-

    4                                                     sp3 (CH4)          sp3            [Zn(CN)4]-2
                                          109.5º                                           [Cd(NH3)4]+2
                                                                                              [FeCl4]-
                               tetrahedral                                                  [Co(Br)4]-2

    4                                       90º
                                                         sp3d2 (XeF4)        dsp2          [Pd(CO)4]+2
                     90º
                                                                                          [Pt(NH3)2Cl2]
                                                                                            [Ni(CN)4]-2
                       square planar
                           a
    5                               90º                  sp3d (PCl5)     d3sp or dsp3        [CuCl5]-3
                e                                                                           [Fe(CO)5]
                                                   e
                                                                           or sp3d
              120º
                                                                                          [Mn(CO)4NO]
                               triangular bipyramidal                                       [Ni(CN)5]-3
                      e        e = equitorial position
                           a   a = axial position


    6                                                    sp3d2 (SF6)       d2sp3 or          [PtCl6]-2
                                                                            sp3d2          [Co(NH3)6]+3
                                             90º
                                                                                           [Fe(OH2)6]+2
                     90º
                                                                                            [Fe(CN)6]-4
                                                                                              [MoF6]-

                                          octahedral                                         [CoF6]-3
                                                                                           [Ni(H2O)6]+2
                                                                                           [Mn(CN)6]-4



Co #7 [UF7]-3, [ZrF7]-3, Co #8 [Mo(CN)8]-4, [TaF8]-3 and Co #9 [UCl3 hydrate] are known but rare.


Coordination Complexes                                                                                    2
 INORGANIC CHEMISTRY


 Types of Ligands:
 Ligands of complex ions are molecules and/or ions with one or more donor atoms that each
 donates a lone pair of electrons to the metal ion to form a covalent bond. Thus, ligands are Lewis
 bases, the metal ion is a Lewis acid, and the complex is a Lewis adduct. Because they have at
 least one lone pair of electrons, donor atoms often come from Groups 5A, 6A, or 7A.
 Ligands are classified in terms of the number of donor atoms, or 'teeth' that each uses to bond to
 the central metal ion.
    Unidentate ligands (Latin, 'one-toothed), such as Cl- and NH3 use a single donor atom.
    Bidentate ligands have two donor atoms, each of which bond to the central metal ion.
    Polydentate ligands have more than two donor atoms.
 Some common ligands in coordination compounds are shown below. Note the lone pair of
 electrons in each donor atom. Bidentate and polydentate ligands give rise to complexes with ring
 structures. For example, ethylenediamine (abbreviated en) has a chain of four atoms
 (:N-C-C-N:), so it forms a 5-membered ring. Such ligands seem to grab the metal ion like a
 crab's claw, so complex ions that contain them are sometimes called chelates (Greek chela =
 crab's claw).


                                                      .. -                                      -                     ..    -
                                 ..                                                 :C N:                            :O H
                               H2O                   : F:                                                              ..
 Unidentate                      ..                    ..
                                                                                  cyanide ion                     hydroxide ion
                                                      .. -                         ..    .. -                       ..          -
                               : NH3                 :Cl :                        :S C N:                          :O N O:
                                                      ..                                                            ..
                                                                               thiocyanate ion                      nitrite ion


                                H2C         CH2                            :O :               :O :

Bidentate                                                                         C       C
                              H2..
                                N             NH2
                                              ..                           :O:                :O: -
                                                                       -    ..                 ..
                          ethylenediamine (en)
                                                                               oxalate ion

                                                                           :O :                                                :O :

                                                                         ..       C     H2C                             CH2   C .. -
                        H2C          CH2     CH2    CH2            -    :O                                                      O:
                                                                                                                                ..
                                                                          ..                  :N      CH2   CH2    N:           ..
                                                                         ..                                                         :
Polydentate                            NH                    NH2
                                                             ..
                                                                       :O..       C     H2C                             CH2   C O -
                                                                                                                                 ..
                   H2..
                     N                 ..                          -
                                                                            :O :                                              : O:
                               diethylenetriamine
                                                                                  ethylenediaminetetracetate (EDTA) ion


 Relative Strengths of Ligands:
 Lewis bases differ in their ability to donate electrons to the metal ion. The relative strengths of
 ligands in coordination complexes has been experimentally determined …


 I- < Br-     < Cl- <     F- < OH- < C2O4-2 < H2O < SCN- < NH3 < en <                                       NO2- < CN- < CO

   WEAK             Increasing ability to donate an electron pair to a metal ion                                        STRONG
   LIGANDS                                                                                                              LIGANDS




 Coordination Complexes                                                                                                               3
INORGANIC CHEMISTRY


Nomenclature of Coordination Compounds:
Lewis bases may be anions, molecules, or (rarely) cations and are called 'ligands'. The donor atom is the
atom of the ligand, which actually donates the electrons (underlined in the table). [* = bidentate ligands]
    formula               name            ligand name          formula                        name           ligand name
                                                                        -
        :NH3           ammonia              ammine                  Cl                       chloride           chloro
                                                                        -
        H2O               water               aqua                  F                        fluoride            fluoro
                                                                                -
        :CO:       carbon monoxide         carbonyl            :CN:                        cyanide            cyano
                                                                            -
        :PH3           phosphine           phosphine                OH                   hydroxide             hydroxo
                                                                      -                                                   -
        :N=O           nitric oxide         nitrosyl             :NO2                         nitrite         nitro (NO2 )
              -                                                       -                                                       -
        NO3               nitrate            nitrato             :NO2                         nitrite        nitrito (ONO )
             -                                                       -2
        NH2               amide              amido              *SO4                         sulfate            sulfato
           -2                                                         -
    *C2O4                 oxalate           oxalato               SCN                    thiocyanate         thiocyanato
          -2                                                        -2
    *CO3               carbonate           carbonato           *S2O3                     thiosulfate          thiosulfato
        -2
        *O                oxide               oxo              C5H5N:                        pyridine          pyridine

Coordination number of a metal is the number of donor atoms to which the metal is bonded. If the
ligands are unidentate, then the coordination number is also the number of ligands. For example, in
         +3                                                                                     +3
[Co(en)3] where each ethylenediamine ligand is bidentate, the coordination number is 6, i.e., Co is
bonded to 6 donor atoms (2 donor atoms from each of 3 ethylenediamine ligands).
Coordination sphere is the metal and its ligands but not the uncoordinated counterions, e.g., in
                                                   +3
[Co(NH3)6]Cl3, the coordination sphere = [Co(NH3)6] .


Nomenclature Rules:
1. If the complex is ionic, name the cation first and the anion second.
2. Within a coordination sphere, name the ligands before the metal
3. Name ligands alphabetically, e.g., ammine before chloro. Prefixes denoting the number of ligands
   (e.g., di in dichloro, tri in triammine, etc.) are not alphabetized, however, prefixes which are part of the
   ligand name are alphabetized, e.g., in dimethylamine [NH(CH3)2] , di is part of the ligand name and so
   is alphabetized.
4. Prefixes bis, tris, tetrakis, pentakis,, etc. are used for ligands that are bidentate, polydentate or already
   have a number prefix as part of its name, e.g., bis(diethylamine) has 2 groups of diethylamine and
   tris(oxalato) because oxalato is bidentate. Prefixes are not alphabetized. Divalent anions are bidentate.
                                                         -2                         -2                  -2
        anionic ligands end in the suffix 'o', e.g., *S2O3 = thiosulfato, *S = sulfido, *CO3 = carbonato
        names of neutral ligands like phosphine (PH3) are usually unchanged except for NH3 (ammine), H2O
         (aqua), CO (carbonyl), and NO (nitrosyl)
5. For metals with multiple oxidation states, indicate the oxidation state in Roman numerals in
   parentheses following the name of the complex ion or molecule.
6. When the complex is neutral or cationic, the name of the central metal atom is the same as the
   element, e.g., chromium, nickel, iron
7. For anionic complexes, the suffix -ate is added to the stem of the metal name, e.g., zincate.
   Latin names of metals are used when the English name is clumsy, i.e.,
   ferrate not ironate                  argentate not silverate                            nickelate
   plumbate not leadate                 cuprate not copperate                              zincate
   stannate not tinate                  chromate                                           manganate
   aurate not goldate                   platinate                                          aluminate




Coordination Complexes                                                                                                            4
INORGANIC CHEMISTRY



                                    WRITING NAMES OF COORDINATION COMPLEXES FROM FORMULAS




         CATIONIC COMPLEXES                                 NEUTRAL COMPLEXES                                 ANIONIC COMPLEXES
 e.g.,       [Cu(NH3)2]NO3                          e.g.,        [Cu(ONO)2]                         e.g.,      K2[Cu(CN)4]


    cationic coordination sphere       anion                neutral coordination sphere                     cation   anionic coordination sphere
                                                                                                            cation   ligandsmetalate(ox#)
         ligandsmetal(ox#)         anion                       ligandsmetal(ox#)
                                                                                                        potassium tetracyanocuprate(II)
           diamminecopper(I) nitrate                           dinitritocopper(II)


   Oxidation number is given only for metals with more than one possible oxidation state. For Ag+, the ox# is not stated.
   Ligands are listed alphabetically. The metal ion is listed after all ligands.
   Note that for anionic complexes (only), the suffix „ate‟ is added to the metal and the Latin name of the metal is used in some cases
    (where pronunciation of the English name is awkward).
   Prefixes di, tri, tetra, penta, hexa, hepta, etc. are used when more than one of a monodentate ligand is present.
   Prefixes bis, tris, tetrakis, pentakis, hexakis, heptakis, etc. are used for bidentate or polydentate ligands, or when the monodentate
    ligand already has a prefix in its name, e.g., bis(dimethylamine)
   For Names: note the space between cationic coordination sphere and the anion and between cation and anionic coordination
    sphere.
   For Formulas: note that there are no spaces in formulas.




Coordination Complexes                                                                                                                             5
INORGANIC CHEMISTRY


Cationic Complexes:
[Co(NH3)6]Cl3                      hexaamminecobalt(III) chloride
[Pt(NH3)4Cl2]+2                    tetraamminedichloroplatinum(IV) ion
[Ag(NH3)2]+                        diamminesilver ion
[Cr(H2O)4Cl2]Cl                    tetraaquadichlorochromium(III) chloride
[Co(H2NCH2CH2NH2)3]2(SO4)3         tris(ethylenediamine)cobalt(III) sulfate
[Fe(H2O)5(SCN)]SO4                 pentaaquathiocyanatoiron(III) sulfate
[Cu(NH3)2(en)]Br2                  diammineethylenediaminecopper(II) bromide

Neutral Complexes:
[Pt(NH3)2Cl4]                      diamminetetrachloroplatinum(IV)
[Co(NH3)3(NO2)3]                   triamminetrinitrocobalt(III)
[Ni(H2NCH2CH2NH2)2Cl2]             dichlorobis(ethylenediamine)nickel(II)
[Ni(CO)4]                          tetracarbonylnickel(0) or nickel tetracarbonyl
[Co2(CO)8]                         octacarbonyldicobalt(0) or dicobalt octacarbonyl

Anionic Complexes:
K3[Co(ONO)6]                       potassium hexanitritocobaltate(III)
[PtCl6]-2                          hexachloroplatinate(IV) anion
Na2[SnCl6]                         sodium hexachlorostannate(IV)
K2[Cu(CN)4]                        potassium tetracyanocuprate(II)
Na2[CrOF4]                         sodium tetrafluorooxochromate(IV)
Na[Al(OH)4]                        sodium tetrahydroxoaluminate
Na2[Sn(OH)6]                       sodium hexahydroxostannate(IV)
K4[Ni(CN)2(ox)2]                   potassium dicyanobis(oxalato)nickelate(II)

In formulas:
   In the coordination sphere, the metal symbol is written first, followed by symbols of its ligands
 Complex ligands are put in parenthesis, even if there is only one ligand is present, e.g., (CN)
    and (OH). Monatomic ligands like Cl, Br, etc. are not parenthesized.
 IUPAC rules state
      inorganic ligands are listed before organic ligands
      anionic ligands are listed before neutral ligands
This last rule can lead to contradictory situations. Indeed literature is rife with examples where
both these rules are ignored. In formulas, it is generally accepted that it is more important to list
the ligands correctly than to place them in order. This leniency is not applied to order of listing
ligands in naming the compounds. Follow the rules carefully for naming compounds.
Name the following coordination compounds:
[Co(en)2Br2]Cl
[Co(PH3)3](NO3)3
[V(NH2)2(NO)2]Cl3
K2[Mn{NH(CH3)2}4(C2O4)2]
[Cr(en)5(SCN)]F2
Na2[MoOCl4]


Coordination Complexes                                                                             6
INORGANIC CHEMISTRY


Coordination Number and Geometry of Coordination Compounds:
No single theory is able to successfully predict the coordination number or geometry of all
coordination complexes. No strict rules can be stated, however, the following generalizations are
helpful.
                                                                                           +2
 The most common coordination number of metal complexes is 6, e.g., [Pt(Cl) 6] . Most of
                                +3   3    +3    6    +2   6         +3  5
    these are octahedral. Cr (d ), Co (d ), Fe (d ), and Fe (d ) favor octahedral complexes
    regardless of the ligands present. For all di- and tri-positive 1st series transition metals, aqua
    ions are octahedral, i.e., [M(H2O6]+2 (or +3).
 4-coordinate complexes are the next most common.                    They exist in two geometries,
    tetrahedral (sp3 hybridized) and square planar (dsp2 hybridized). Tetrahedral geometries
    (bond angles = 109.5) are sterically favored over square planar (bond angles = 90).
                                                                                                      -
 4-coordinate complexes of non transition metals are almost always tetrahedral, e.g., [AlCl4]
    and SnBr4.
 4-coordinate complexes of the transition metals may exist in either form. Tetrahedral
    complexes are especially favored when ligands are weak and relatively large (e.g., Br -) and
    metal ions are relatively small, i.e., 1st transition metal series complexes, e.g., VCl4, [FeCl4]-,
    [NiBr4]-, [MnCl4]-2, [CdCl4]-2 .
       +2
 Ni      (3d8) displays square planar geometry with small strong ligands like CN-, tetrahedral
    complexes with large weak ligands like F-, Cl-, Br-, I- and forms octahedral complexes with
    NH3 and H2O.
                                                                  8                           +2
 Square planar complexes are more common for larger d transition metals, i.e., Pd               (4d8),
       +2     8          +3   8
    Pt (5d ), and Au (5d ). Steric constraints are relaxed with these larger metal ions. Less
    commonly, square planar complexes are also seen with Co+2 (d7), Co+3 (d6) and Cr+2 (d4).
 2-coordinate transition metal complexes (sp hybridized) are restricted to +1 ions of Group IB,
    i.e., Cu+ (3d10), Ag+ (4d10) and Au+ (5d10) and +2 ions of Group 2B, i.e., Zn+2, Cd+2 and Hg+2.
 Odd coordination numbers (1,3,5) are very rare.
Note that a given transition metal ion can form complexes of differing coordination numbers.
  Co+2 (3d7) forms both octahedral and tetrahedral complexes
  Ni+2 (3d8) forms octahedral, tetrahedral, and square planar complexes (as previously stated).

Valence Bond Theory of Transition Metal Coordination Compounds:
VB theory treats metal to ligand (donor group) bonds as coordinate covalent bonds, formed when
a filled orbital of a donor atom overlaps with an empty hybrid orbital on the central metal atom.
The molecular geometry is predicted using VSEPR.
The theory proposes that the number of metal-ion hybrid orbitals occupied by donor atom lone
pairs determine the geometry of the complexes. Lone pairs of electrons are ignored. Since lone
pairs are in the inner shell, they are believed to have little effect on molecular geometry.

2-Coordinate Compounds:
Linear sp hybridized transition metal complexes:
a. Consider [Ag(NH3)2]+ Ag = 5s1 4d10         Ag+ = 5s 4d10
                 4d         5s     5p                                  sp        5p
                                              sp
       +                                                         +
    Ag                                                  [Ag(NH3)2]
                                           hybridized

                                                                     :NH3 :NH3



Coordination Complexes                                                                               7
INORGANIC CHEMISTRY


b. Consider [Cu(CN)2]- Cu = 4s1 3d10 Cu+1 = 4s 3d10
                   3d             4s        4p                                            sp          4p
                                                           sp
                                                                                  -
    Cu+                                                                 [Cu(CN)2]
                                                       hybridized
                                                                                                                         -
                                                                                              -            K+ : C   N:
                                                                                        CN- CN


Problem: Predict the hybridization state and molecular geometry of [AuCl2]-



Note that when transition metals ionize, electrons from the (n+1)s orbitals are usually removed
before those of the nd orbital (even though the (n+1)s orbital is filled before the nd orbital).
This behavior can be abbreviated as FIFO (First In, First Out, i.e., (n+1) orbitals are first to be
filled when building up the electron configuration of the neutral atom, and first to be emptied
during ionization).
The preferential removal of (n+1)s electrons is not surprising, since the (n+1)s electrons are
farther from the nucleus (held less strongly) than nd electrons.


Four Coordinate Compounds: (Tetrahedral Complexes)
a. Consider [ZnCl4]-2             Zn = 4s2 3d10            Zn+2 = 4s 3d10

                        3d             4s        4p                                             sp3
                                                                sp3
       Zn+2                                                                 [ZnCl4]-2
                                                           hybridized
                                                           tetrahedral
                                                                                                    -  -
                                                                                          Cl- Cl- Cl Cl


b. Consider [Cd(NH3)4]+2 Cd = 5s2 4d10 Cd+2 = 5s 4d10
                                            5s        5p                                              sp3
                             4d                                       sp3
          Cd
              +2                                                                [Cd(NH3)4]+2
                                                                 hybridized
                                                                 tetrahedral
                                                                                               ..  ..  .. ..
                                                                                               NH3 NH3 NH3 NH3



Note that all 4-coordinate complexes of a s d10 ion are sp3 hybridized and tetrahedral, e.g.,
   4-coordinate complexes of Group 2B M+2 ions: Zn+2, Cd+2, Hg+2
   4-coordinate complexes of Group 1B M+1 ions: Cu+1, Ag+1, Au+1




Coordination Complexes                                                                                                       8
INORGANIC CHEMISTRY


In four coordinate complexes of s0d8 ions (Ni+2, Pd+2, Pt+2), two molecular geometries are
encountered, tetrahedral (sp3) and square planar (dsp2).
Consider [NiCl4]-2      Ni = 4s2 3d8          Ni+2 = 4s0 3d8
                                                     sp3
               3d           4s        4p          hybridized                     3d            sp3
     +2                                                                -2
   Ni                                                            [NiCl4]
                                                 tetrahedral


As in previous examples of tetrahedral, sp3 hybridized complexes, the ligand donates electrons to
the vacant sp3 hybrid orbitals. This is true when large, weak ligands are present. However, with
small, strong ligands, such as CN-, two unpaired electrons in half-filled 3d orbitals are forced to
pair up with each other, creating an empty 3d orbital. This gives rise to dsp2 hybridization and the
square planar geometry seen in the following examples.


Four Coordinate Compounds: (Square Planar Complexes):
When very strong ligands are present, four-coordinated d8 metal ions usually form square planar
complexes (rather than tetrahedral).
Consider [Ni(CN)4]-2 Ni = 4s2 3d8               Ni+2 = 4s 3d8
               3d          4s        4p            dsp2                           3d          dsp2           4p
                                                 hybridized [Ni(CN) ]-2
  Ni+2                                                             4

              3d           4s        4p
                                                  square                                  -          -   -
                                                                                        CN CN- CN CN
                                                  planar

In dsp2 hybridization, one d-orbital is empty and receives an electron pair from the ligand. Donor
atoms are situated on the x and y -axes of the square planar structure.

Note that in the term 'dsp2', 'd' precedes 'sp2' indicating that the d-orbital used in hybridization
comes from a lower (inner) shell than the 's' and 'p' orbitals. This is called inner shell
hybridization. In the previous unit on bonding, we saw terms such as 'sp3d'. In this case, where
'd' follows 'sp3', the d-orbital is from the highest energy level, e.g., recall that PCl5 has sp3d
hybridization (triangular bipyramidal geometry). This is called outer shell hybridization.


Six Coordinate Complexes (Octahedral):
Six ligand donor atoms in an octahedral complex are located at the corners of an octahedron.
Valence bond postulates that the orbitals best shaped and best oriented to receive electron pairs
from these directions are the dx2-y2 and dz2 orbitals (directed on the x, y, and z-axes).
Consider [Fe(CN)6]-3      Fe = 4s2 3d6          Fe+3 = 4s0 3d5
                   3d           4s        4p
         +3
    Fe
                                                      d2sp3                                    d2sp3
                   3d       4s            4p        hybridized                   3d
                                                                            -3
                                                                   [Fe(CN)6]
    Fe+3
                                                    octahedral

                                                                                       CN- CN- CN- CN- CN- CN-



Coordination Complexes                                                                                            9
          INORGANIC CHEMISTRY


          CN- is a strong field donor, forcing inner 3d electrons into a lower spin state and hybridizing
          inner 3d orbitals, i.e., d2sp3 (inner shell hybridization). H2O, a weaker field donor, is not able to
          bring about inner shell hybridization and the resulting hybridization is thus sp3d2. Both d2sp3 and
          sp3d2 complexes are octahedral.
          Consider [Fe(H2O)6]+3 Fe = 4s2 3d6                                       Fe+3 = 4s0 3d5
                 3d          4s         4p                              4d                          sp 3d2          3d                 sp 3d2             4d
                                                                                                hybridized
     +3
Fe
                                                                                                octahedral
                                                                                                                           +3
                                                                                                              [Fe(H2O)6]
                                                                                                                                H2O H2O H2O H2O H2O H2O

          Metal ions in which two d-orbitals are vacant will form inner shell hybridized d2sp3 octahedral
          complexes.
          Metal ions in which two d-orbitals are not vacant will form either outer shell sp3d2 hybridized
          octahedral complexes (with weak ligands) or inner shell d2sp3 hybridized octahedral complexes
          with strong ligands (If half-filled d-orbitals are present a low spin state can be forced).
          Study the following examples and note where inner and outer shell hybridization occur and why.
                                                                    x   = an electron pair donated from a ligand
                                                                    x
           d6     Co+3
                                  3d                        4s              4p                          4d
           [Co(NH3)6]+3                 x       x           x           x       x       x                        strong ligand
                                        x       x           x           x       x       x

                                                         d2sp 3
                                  3d                        4s              4p                          4d
                                                            x           x       x       x       x   x
             [CoF6]-3                                       x           x       x       x       x   x            weak ligand

                                                                            sp 3d2

           d5 Mn+2
                              3d                        4s              4p                          4d
                      -4           x        x           x           x       x       x
           [Mn(CN)6]               x        x           x           x       x       x

                                                        d2sp 3


           d8     Ni+2


                                  3d                        4s                  4p                      4d
                                                             x          x       x       x       x   x
           [Ni(H2O)6]+2                                      x          x       x       x       x   x


                                                                            sp 3d2

            d3      Cr+3

                                   3d                        4s                 4p                       4d
           [Cr(NH3)6]   +3                  x       x           x           x       x       x
                                            x       x           x           x       x       x

                                                             d2sp 3
          Coordination Complexes                                                                                                                          10
INORGANIC CHEMISTRY


Sample Problems:
1.   Draw the Lewis structure of the product of the following
     PH3   + AlBr3       




     Write the formula of the Lewis acid: ……………………………………….
     Write the formula of the Lewis base: ………………………………………
2.    Consider [Hg(CN)2]
     a) name it …………………………………………………………………………
     b) state its molecular geometry …………………………………………………
     c) name its hybridization state …………………………………………………..
     d) use Valence Bond theory to show how it bonds




3.   Consider [ZnI3]-, a 3-coordinate complex
     a) name it …………………………………………………………………………
     b) predict its molecular geometry …………………………………………………
     c) predict its hybridization state …………………………………………………..
     d) use Valence Bond theory to show how it bonds




Coordination Complexes                                          11
INORGANIC CHEMISTRY


4.   Consider [Ni(CN)5]-3, a 5-coordinate complex
     a) name it …………………………………………………………………………
     b) predict its molecular geometry …………………………………………………
     c) use Valence Bond theory to show how it bonds assuming inner shell hybridization




5.   Name the following complexes:
     a) K[Sb(C2O4)2(NH2)2]


     b) [Mn(OH)2{NH(CH3)2}4Br](SO4)2


     c) K[BF4]


     d) [W(CO)2(NO2)3F](NO3)2



6.   Write formulas for the following complexes:
     a) potassium hexafluoroantimonate(V)




     b) sodium octacyanomolybdate(IV)




     c) tetraamminediaquazirconium(IV) bromide




     d) nitratodiphosphinethiocyanatopalladium(IV) nitrate




Coordination Complexes                                                                    12

				
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