Complexes

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Complexes
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Complexes
Compounds in which a metal atom or ion is
surrounded by a number of oppositely charged ions
or by neutral molecules. All possessing lone
pairs of electrons which are available for
donation to vacant orbitals of the metal atom or
ion.
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Structure
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Central ions, atoms Transition metals Alkaline
earth metals Alkaline metals
Coordination numbers Number of ligands in the
first coordination sphere
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Complexes with various coordination numbers Complexes with various coordination numbers
Coordination number Complex
2 Ag(NH3)2, CuCl2-
3 HgI3-
4 Zn(NH3)42, Ni(CN)42-
5 Ni(CN)53-, Fe(CO)5
6 Cr(H2O)63, Fe(CN)63-
7 ZrF73-
8 Mo(CN)84-
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Geometry
linear (2)
tetrahedral (4)
octahedral (6)
square planar (4)
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Monodentate Ligands
Cations H2N-NH3 Anions F-, Cl-, OH-,
CN-, NO3-, NO2- Neutral molecules H2O, NH3,
CO
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Water
Ammonia
Chloride ion
Cyanide ion
Carbon monoxide
Hydroxide ion
Thiocyanate ion
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Polydentate Ligands
Ethylenediamine (en)
Glycinate ion (gly-)
Oxalate ion
Ethylenediaminetetraacetate ion (EDTA4-)
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Chelates
Bi- or polydentate ligands
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Nomenclature IUPAC

• Cation preceeds anions
• Ligands preceed central ions or atoms
• Anion ligands -o ending (hydroxo, chloro,
  cyano)
• Cations, neutral molecules unchanged
• Exception(!) aqua, ammine, carbonyl, nitrosyl
• Complex anions -ate ending
• Oxidation state Roman numbers

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Dissociation of complexes
Formula Conductance Number of ions Number of chloride ions
Pt(NH3)6Cl4 523 5 4
Pt(NH3)5ClCl3 404 4 3
Pt(NH3)4Cl2Cl2 228 3 2
Pt(NH3)3Cl3Cl 97 2 1
Pt(NH3)2Cl4 0 0 0
KPt(NH3)Cl5 108 2 0
K2PtCl6 256 3 0
Molar conductance cm2/??mól, 0,001M, 25C
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Stability constant, formation
Properties of metal complex differ from metal ion!

1. Colour changing
2. Solubility
3. Ligand reactions
4. Number of particles, dissociation

Formation constant Kstab (stability constant)
Pl. Ag 2NH3 Ag(NH3)2
Dissociation constant
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Izomerism


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cis
trans
dichloro-tetraammine-cobalt(III) ion
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dichloro-bis(etylenediammine)cobalt(III)
ion en etylenediammine
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Bonding in complexes

• Valence Bond Theory
• Crystal Field Theory