Transcript Transition Metals and Coordination Chem

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- CN2
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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)
F
F
CN = 5
Trigonal bipyramidal
Br
F
Square Pyramide
I
F
CN = 6
I
I
F
P
Octahedral
F
F
I
I
F
F
F
Br
F
S
F
F
F
F
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Coord
Number
Coordinated Complexes and
Coordination Number
Shape
2
Linear
4
Square Planar
Example
[CuCl2]-, [Ag(NH3)2]+, [AuCl2]-
[Ni(CN)4] 2-, [PdCl4]2[Pt(NH3)4] 2+, [Cu(NH3)4] 2+
F
F
Br
F
F
4
Tetrahedral
6
Octahedral
[Cu(CN)4] 3-, [Zn(NH3)4]2+
[CdCl4] 2-, [MnCl4] 2-
[Cu(H2O)6] 3+, [V(CN)6] 4-,
F
[Cu(NH3)4Cl2] +, [Co(en)3] 3+
F
F
S
F
F
F
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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
[EDTA]4- 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 IHydroxo OHCyano 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)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
Ni(H2O)62+ + 3en  Ni(en)3 + 6H2O
kf = 4•108
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
Chlorophyll
Oxymyoglobin
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Ferrichrome
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Nomenclature
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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Rules:
Nomenclature
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
Lead: Plumbate
Gold: Aurate
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Copper: Cuprate
Silver: Argentate
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)2]Br2
f) bis(ethylenediamine)zinc(II) tetraiodomercurate(II)
[Zn(en)2][HgI4]
More anionic metals
Osmium:
Osmate
Amtimony: Antimonate
Platinum: Platinate
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Cobalt:
Rhenium:
Rhodium:
Cobaltate
Rhenate
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
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