2302_CoordChem

January 13 1 Nomenclature & Coordination Chem

24.2 Nomenclature and Coordination Chemistry

Dr. Fred Omega Garces Chemistry 201 Miramar College


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-


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.

Complex - Metal ion bonded to a number of ligands

M

M M

M

M


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.


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

F

F

B r

FF

I

II

P

I

I

I

F F

B r

F

F

F

F

F

F

S

F

F

F


Coordinated Complexes and Coordination Number Coordination

Number Geometry 3-D Model Example

2

Linear

[CuCl2]-, [Ag(NH3)2]+, [AuCl2]-

4

Square

Planar

[Ni(CN)4] 2-, [PdCl4]2-

[Pt(NH3)4] 2+, [Cu(NH3)4] 2+

4

Tetrahedral

[Cu(CN)4] 3-, [Zn(NH3)4]2+

[CdCl4] 2-, [MnCl4] 2-

6

Octahedral

[Cu(H2O)6] 3+, [V(CN)6] 4-,

[Cu(NH3)4Cl2] +, [Co(en)3] 3+

F

F

B r

FF

F

F

F

S

F

F

F


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),


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 Bromo Br-

Carbonyl CO Iodo I- Hydroxo OH-

Cyano CN-


Other polyatomic ions that can be ligands


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


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


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).


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.


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.


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 Iron: Ferrate Copper: Cuprate Lead: Plumbate Silver: Argentate Gold: Aurate Tin: Stannate


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 Osmium: Osmate Cobolt: Cobaltate Amtimony: Antimonate Rhenium: Rhenate Platinum: Platinate Rhodium: Rhodate


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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