Nomenclature

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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
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 sphere. 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
• Square Pyramide
• CN 6 Octahedral

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Coordinated Complexes and Coordination Number

• Coord Shape Example
• Number
• 2 Linear CuCl2-, Ag(NH3)2, AuCl2-
• 4 Square Planar Ni(CN)4 2-, PdCl42-
• Pt(NH3)4 2, Cu(NH3)4 2
• 4 Tetrahedral Cu(CN)4 3-, Zn(NH3)42
• 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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Ligands

• Consider Ag(NH3)2
• Ligand (contains the donor atom, directly bonded
  to metal)
• NH3 - ligand occupy one site in coordinate
  sphere (monodentate)
• 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
• EDTA4- or (ethylenediaminetetraacetate),
  phenylpyridine

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Ligands

• 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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Chelates

• 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)33 Pt(en)22
• 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
  4108
• Ni(H2O)62 3en ? Ni(en)3 6H2O kf
  21018
• 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

• Chlorophyll
• Oxymyoglobin Ferrichrome

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Nomenclature

• Cation - Anion Salts name cation before anions
  i.e., Co(HN3)5ClBr2, 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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Nomenclature

• Rules
• 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) K3Au(CN)4
• Potassium Tetracyanoaurate(I)
• d) KCo(C2O4)2(NH3)2
• Potassium diaminedioxaloCobaltate(I)
• f) Cr(en)2F2NO3
• 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
• PtCl2(en)2Br2
• f) bis(ethylenediamine)zinc(II)
  tetraiodomercurate(II)
• Zn(en)2HgI4
• More anionic metals
• Osmium Osmate Cobalt Cobaltate
• Amtimony Antimonate Rhenium Rhenate
• Platinum Platinate Rhodium Rhodate

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Geometry

• 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