Download 24.2 Nomenclature and Coordination Chemistry

24.2 Nomenclature and
Coordination Chemistry
Dr. Fred Omega Garces
Chemistry 201
Miramar College
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Nomenclature & Coordination Chem
January 13
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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Nomenclature & Coordination Chem
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Metal-Ligand: Lewis Acid - Lewis Base
Metal; possesses open orbital to
accept e- pair(s) through their
empty d-orbital(s)
Ligand; possess e- pair to donate
to metal.
Combine to form LA-LB
(Compound)
In general, the complex is more
stable than the separated
compound.
M
M
M
M
M
Complex - Metal ion bonded to a
number of ligands
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Complex - Metal coordinating to Ligands
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 atoms are those elements that are directly bonded to
each other and are contained in the coordination sphere.
Counter ions atoms or ions that are denoted 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, that is the ligands and central metal
ion remain attached.
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Nomenclature & Coordination Chem
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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)
F
CN = 5
F
Trigonal bipyramidal
Br
Square Pyramide
I
F
F
CN = 6 Octahedral
I
I
P
F
F
F
I
I
F
F
F
S
F
Br
F
F
F
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Nomenclature & Coordination Chem
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January 13
Coordinated Complexes and Coordination Number
Coordination
Number
2
4
Geometry
3-D Model
Example
[CuCl2]-, [Ag(NH3)2]+, [AuCl2]-
Linear
Square
[Ni(CN)4] 2-, [PdCl4]2-
F
F
[Pt(NH3)4] 2+, [Cu(NH3)4] 2+
Br
Planar
F
F
4
6
[Cu(CN)4] 3-, [Zn(NH3)4]2+
[CdCl4] 2-, [MnCl4] 2-
Tetrahedral
F
Octahedral
[Cu(H2O)6] 3+, [V(CN)6] 4-,
F
[Cu(NH3)4Cl2] +, [Co(en)3] 3+
F
S
F
F
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Nomenclature & Coordination Chem
January 13
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.
ethylenediamine (en), oxalate, 1.10 phenanthroline,
carbonate, bipyridine, phenylpyridine,
[EDTA]4- or (ethylenediaminetetraacetate),
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Nomenclature & Coordination Chem
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Ligands
Example of Typical Uni-, bi- and poly dentate Ligands
Name of Neutral and Anionic Ligands:
Neutral:
Anionic -ends in "o"
Aqua H2O
Fluoro Fl-
Amine NH3
Chloro Cl-
Nitrosyl NO
Carbonyl CO
Bromo BrIodo IHydroxo OHCyano CN-
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Nomenclature & Coordination Chem
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Other polyatomic ions that can be ligands
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Nomenclature & Coordination Chem
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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)3]3+ [Pt(en)2]2+
EDTA ethylenediaminetetraacetate
(picture) hexadentate
EDTA is the antidote for
heavy metal poisoning
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Nomenclature & Coordination Chem
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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
Zn – Zinc finger protein
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Nomenclature & Coordination Chem
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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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Nomenclature & Coordination Chem
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Nomenclature
Cation - Anion: Salts: name cation before anions i.e., [Co(HN3)5Cl]Br2, we
name [Co(NH3)5Cl] complex ion before bromides counter ions .
Complex: Within complex ion, the ligands are named in alphabetical order
before the metal i.e., pentaaminechlorocobalt(II), note that penta is an
indication of the number of NH3 group, and not considered in the
alphabetization of the ligands.
Ligand: Anionic ligands end in -o and neutral ligands are name based on their
molecular name (exceptions 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 tris(bipyridine)iridium (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 & Coordination Chem
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Nomenclature
Rules, chemical Formulas:
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.
Rules, chemical Naming:
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 24.2 BLB
a) [Cr(en)2F2]NO3
b) K3[Au(CN)4]
c) K[Co (NH3)2(C2O4)2]
Naming anionic metals
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Iron:
Ferrate
Copper:
Cuprate
Lead:
Plumbate
Silver:
Argentate
Gold:
Aurate
Tin:
Stannate
Nomenclature & Coordination Chem
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Example: Formula from Name
Name from formula 24.7 BLB
a) Hexaamminechromium(III) nitrate
d) dichlorobis(ethylenediamine)platinum(IV) bromide
f) bis(ethylenediamine)zinc(II) tetraiodomercurate(II)
More anionic metals
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Osmium:
Amtimony:
Osmate
Antimonate
Cobolt:
Rhenium:
Cobaltate
Rhenate
Platinum:
Platinate
Rhodium:
Rhodate
Nomenclature & Coordination Chem
January 13
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.,
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FeF63- and FeCl4- only
Nomenclature & Coordination Chem
January 13