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05.06.01 10:39 PM 1 Nomenclature & Nomenclature & Coordination Chem Coordination Chem

Basic Coordination Chemistry

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Page 1: Basic Coordination Chemistry

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Nomenclature & Nomenclature & Coordination ChemCoordination Chem

Page 2: Basic Coordination Chemistry

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Lewis Acid - Lewis Base Lewis Acid - Lewis Base ChemistryChemistry

Lewis Acid : eLewis Acid : e-- acceptor acceptor

(metals are good e- acceptor)(metals are good e- acceptor)

Lewis Base : eLewis Base : e-- donor donor

(Ligands with lone pair electrons)(Ligands with lone pair electrons)

Ligands, atoms or cluster of atoms with lone pair electrons available to Ligands, atoms or cluster of atoms with lone pair electrons available to donatedonate

Complexing Agent: HComplexing Agent: H22O, NHO, NH33, Cl, Cl-- CN CN--

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Metal possesses open orbitals to Metal possesses open orbitals to accept eaccept e-- pair. pair.

M with empty d- orbitalsM with empty d- orbitals

Ligand with eLigand with e-- pair pair

Combine to form LA-LB (Compound)Combine to form LA-LB (Compound)In general, the complex is more stable than the separated compound.In general, the complex is more stable than the separated compound.

Complex Complex - Metal ion bonded to a number of ligands- Metal ion bonded to a number of ligands

MM MM

MM MM

MM

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Complex -Complex -

Metal- Ligand compounds [ML[MLnn] i.e., [Ag(NH] i.e., [Ag(NH33))22]]+ + or [Co(NHor [Co(NH33))66]] ClCl33[ ] denotes atoms bonded to each other [ ] denotes atoms bonded to each other through covalent bonds. These atoms are through covalent bonds. These atoms are contained in the contained in the coordination spherecoordination sphere..

Coordinated sphere is the directly bonded to each other.Coordinated sphere is the directly bonded to each other.Counter ions are outside bracket, and are not part of the coordinate Counter ions are outside bracket, and are not part of the coordinate sphere.sphere.

A coordinated compound behaves like an electrolyte in water: the A coordinated compound behaves like an electrolyte in water: the complex ion and counter separates from each other. But the complex ion and counter separates from each other. But the complex ion behaves like a polyatomic ion: the ligands and central complex ion behaves like a polyatomic ion: the ligands and central metal ion remain attachedmetal ion remain attached..

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Coordination NumberCoordination NumberCN - Number of ligand atoms bonded directly to the central metal ionNumber of ligand atoms bonded directly to the central metal ion..

Specific for given metal ion in particular Oxidation #.Specific for given metal ion in particular Oxidation #.i.e.,i.e., [Co(NH[Co(NH33))66]]++ CN = 6CN = 6 Ligand # = 6Ligand # = 6

[Ag(NH[Ag(NH33))22]]++ CN = 2CN = 2 Ligand # = 2Ligand # = 2[Co(en)[Co(en)33]]++ CN = 6CN = 6 Ligand # = 3Ligand # = 3

Geometry of Complex is related to CN.Geometry of Complex is related to CN.

CN = 2CN = 2 LinearLinear CN= 4CN= 4 Tetrahedral (dTetrahedral (d1010) )

Sq Planar (dSq Planar (d88))

CN = 5CN = 5 Trigonal bipyramidalTrigonal bipyramidal

Square PyramideSquare Pyramide

CN = 6CN = 6 OctahedralOctahedral

F

F

F

S

F

F

F

F

F

Br

F

F

I

II

P

I

I

I

F F

Br

F

F

F

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Coordinated Complexes and Coordinated Complexes and Coordination Number Coordination Number

Coord Shape ExampleNumber

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

Br

F

F

F

F

F

S

F

F

F

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LigandsLigandsConsider [Ag(NH3)2]+

Ligand Ligand (contains the donor atom, directly bonded to metal)(contains the donor atom, directly bonded to metal)

::NNHH33 - ligand occupy one site in coordinate sphere (monodentate) - ligand occupy one site in coordinate sphere (monodentate)

examples (Monodentate)examples (Monodentate)NN3-3- , X , X--, CN, CN- - , OH, OH--,, NH NH33 , pyridine, H , pyridine, H22OO

Polydentate ligand - known as chelating agentsPolydentate ligand - known as chelating agents - ligand which has several donor sites that can multi-- ligand which has several donor sites that can multi-bond (coordinate) metal simultaneously (chelatesbond (coordinate) metal simultaneously (chelates))i.e. en, oxalate, 1.10 phenanthroline, carbonate, bipyridinei.e. en, oxalate, 1.10 phenanthroline, carbonate, bipyridine

[EDTA][EDTA]4-4- or (ethylenediaminetetraacetate), phenylpyridine or (ethylenediaminetetraacetate), phenylpyridine

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LigandsLigandsExample of Typical mono-, bi- and poly dentate LigandsExample of Typical mono-, bi- and poly dentate Ligands

Name of Neutral and Anionic Name of Neutral and Anionic Ligands:Ligands:

Neutral: Neutral: AnionicAnionic

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 Chelates Chelating Ligands have two or more donor atoms Chelating Ligands have two or more donor atoms

that simultaneously coordinate to a single metal ion.that simultaneously coordinate to a single metal ion.

Polydentate - (Many toothed - ligand) Polydentate - (Many toothed - ligand)

Chelating agent (Claw)Chelating agent (Claw)

Sequestering agent - sequester - to set apart or Sequestering agent - sequester - to set apart or separateseparate

enen ethylenediamine (shown) - two toothed ligand:ethylenediamine (shown) - two toothed ligand:

i.e., [Co(en)i.e., [Co(en)33]]3+3+ [Pt(en)[Pt(en)22]]2+2+

EDTAEDTA ethylenediaminetetraacetate ethylenediaminetetraacetate

(picture) hexadentate(picture) hexadentate

EDTA is the antidote for EDTA is the antidote for

heavy metal poisoningheavy metal poisoning

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Chelating agents in Living Chelating agents in Living systemsystem

Seven of 24 elements necessary for life, Seven of 24 elements necessary for life, based on ability to formed complexesbased on ability to formed complexes

V, Cr, Mn, Fe, Co, Cu, ZnV, Cr, Mn, Fe, Co, Cu, Zn

Fe - hemoglobin, chlorophyll (Mg)Fe - hemoglobin, chlorophyll (Mg)

Co - Vitamin BCo - Vitamin B

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Chelating effectChelating effect

A complex containing chelate ligands is more stable A complex containing chelate ligands is more stable than that from a monodentate ligand.than that from a monodentate ligand.

KKff, larger for chelating complex., larger for chelating complex.

Ni(HNi(H22O)O)662+ 2+ + 6NH+ 6NH33 Ni(NH Ni(NH33))66 + 6H + 6H22O O kkff = 4•10 = 4•1088

NiNi((HH22O)O)662+2+ + 3en + 3en Ni(en) Ni(en)33 + 6H + 6H22O O kkff = 2•10 = 2•101818

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 Biological Coordinating ComplexesComplexes

ChlorophyllChlorophyll

Oxymyoglobin FerrichromeOxymyoglobin Ferrichrome

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NomenclatureNomenclatureCation - Anion: Cation - Anion: Salts: name cation before anions i.e., Salts: name cation before anions i.e.,

[Co(HN[Co(HN33))55Cl]BrCl]Br22, we name [Co(HN, we name [Co(HN33))55Cl] complex ion before Cl] complex ion before bromides counter ions .bromides counter ions .

Complex: Complex: Within complex ion, the ligands are named in Within complex ion, the ligands are named in alphabetical order before the metal i.e., alphabetical order before the metal i.e., tetraaminechlorocobalt(II),tetraaminechlorocobalt(II), note that tetra is an indication of the number of NHnote that tetra is an indication of the number of NH33 group, and not group, and not considered in the alphabetizing of the ligand.considered in the alphabetizing of the ligand.

Ligand: Ligand: Anionic ligands end in -o and neutral ligands are name Anionic ligands end in -o and neutral ligands are name based on their molecular name (excepts are aqua Hbased on their molecular name (excepts are aqua H22O, amine: NHO, amine: NH33))Greek prefixes are used to indicate number of ligands, di-, tri-, tetra-, penta-, hexa-. 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 Exception occurs when ligand already has Greek prefix in its name, The prefixes bis-, tris-, tetrakis-, pentakis, & hexakis. are used instead.bis-, tris-, tetrakis-, pentakis, & hexakis. are used instead.

i.e., Ir(bpy)i.e., Ir(bpy)33 trisbipyridineiridium trisbipyridineiridium (III) bipyridine already has bi in its name.(III) bipyridine already has bi in its name.

If the complex is an anionIf the complex is an anion, , then its name ends with suffix -ate.then its name ends with suffix -ate.Further more, oxidation state of the metal is given in roman Further more, oxidation state of the metal is given in roman

numerals in parenthesis at the end of the name.numerals in parenthesis at the end of the name.

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NomenclatureNomenclatureRules: Rules:

1. The cation is written before the anion.1. The cation is written before the anion.

2. The charge of the cation(s) is balanced by the charge of the 2. The charge of the cation(s) is balanced by the charge of the anion(s).anion(s).3. For the complex ion, neutral ligands are written before anionic 3. For the complex ion, neutral ligands are written before anionic

ligands (negative charge), and the whole ion is placed in ligands (negative charge), and the whole ion is placed in brackets.brackets.

Procedure Outline:Procedure Outline:1. The cation is named before the anion.1. The cation is named before the anion.2. Within the complex ion, the ligands are named, in alphabetical 2. Within the complex ion, the ligands are named, in alphabetical order.order.3. Neutral ligands generally have the molecule name.3. Neutral ligands generally have the molecule name.

Anionic ligands drop the -ide and add -o after the root name.Anionic ligands drop the -ide and add -o after the root name.4. Numerical prefixes denote the number of a particular ligand.4. Numerical prefixes denote the number of a particular ligand.5. Oxidation state of metal ion is in Roman numeral in parenthesis.5. Oxidation state of metal ion is in Roman numeral in parenthesis.6. For anionic complex, 6. For anionic complex, the end of the metal name is replaced by -the end of the metal name is replaced by -ate.ate.

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Example: Naming from Example: Naming from FormulaFormula

Name from formulaName from formula

a) Ka) K33[Au(CN)[Au(CN)44]]

Potassium Tetracyanoaurate(I)Potassium Tetracyanoaurate(I)

d) K[Co(Cd) K[Co(C22OO44))22(NH(NH33))22]]

Potassium diaminedioxaloCobaltate(I)Potassium diaminedioxaloCobaltate(I)

f) [Cr(en)f) [Cr(en)22FF22]NO]NO33

Bis(ethylenediamine)difluorochromium(III) nitrateBis(ethylenediamine)difluorochromium(III) nitrate

Naming anionic metalsNaming anionic metals Iron: Iron: FerrateFerrate Copper:Copper: CuprateCuprateLead:Lead: PlumbatePlumbate Silver:Silver: ArgentateArgentateGold:Gold: AurateAurate Tin:Tin: StannateStannate

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Example: Formula from Example: Formula from NameName

Name from formulaName from formula

a) Hexaamminechromium(III) nitratea) Hexaamminechromium(III) nitrate

[Cr(NH[Cr(NH33))44] (NO] (NO33))33

d) dichlorobis(ethylenediamine)platinum(IV) bromided) dichlorobis(ethylenediamine)platinum(IV) bromide

[PtCl[PtCl22(en)(en)22]Br]Br22

f) f) bis(ethylenediamine)zinc(II) tetraiodomercurate(II)bis(ethylenediamine)zinc(II) tetraiodomercurate(II)

[Zn(en)[Zn(en)22][HgI][HgI44]]

More anionic metalsMore anionic metals Osmium:Osmium: OsmateOsmate Cobalt:Cobalt: CobaltateCobaltateAmtimony:Amtimony: AntimonateAntimonate Rhenium:Rhenium: RhenateRhenatePlatinum:Platinum: PlatinatePlatinate Rhodium:Rhodium: RhodateRhodate

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GeometryGeometryCoordinate Number (CN):Coordinate Number (CN):Number of donor atoms bonded to metalNumber of donor atoms bonded to metal2- coordinate - linear4 - coordinate tetrahedral and square planar

ML4 , Pt(II) is always CN = 46- octahedral

ML6, Cr(III) and Co(III) CN = 6

CN influence byCN influence by Size of metal ion

Small metal /large ligand - Low coordinate numberSmall metal /large ligand - Low coordinate numberSurrounding ligand

Large metal / small ligand - High coordination numberLarge metal / small ligand - High coordination numberi.ei.e., FeF., FeF66

3-3- and FeCl and FeCl44-- only only