Coordination Complex - Advanced Inorganic Chemistry | CHE 3340, Study notes of Inorganic Chemistry

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Coordination

Complexes: An

Introduction

Chapter 7

Transition Metal Complexes—

Applications of HSAB Theory

 Ligands

 (^) Ions or molecules that donate e ^ pair to metal  (^) Lewis base

 Metal

 (^) Lewis Acid  (^) Can accept more than 1 Ligand (Lewis base)

 M—L bond = Coordinate covalent bond

 (^) = Lewis acid base adduct formation

Coordination Complexes

 (^) Central metal atom surrounded by set of ligands. 3+ 2  2

2. Chelate Ligands

 Have 2 or more atoms on one molecule

with lone pairs

 (^) Each of which can simultaneously form 2 e bond to M n+  (^) Usually 5 or 6-membered rings with M  (^) Sometime form 4-membered rings  (^) Must be nonlinear molecules L L M

Bidentate Ligands  (^) 2 possible sites of attachment  (^) 2 Lewis base sites that can attach to Mn+ O O^  N N N N  O O  O O H 2 N NH 2 1,10-phenanthroline (phen) 2,2’-bipyridine (bpy) Ethylenediamine (en) Oxalate (ox 2  ) Acetylacetonate (acac  )

Stability Constants  (^) Measure of selectivity of ligand for Metal ion  (^) Nature of ligand  (^) Coordination geometries common to metal  (^) Oxidation state of Metal [M(H 2

O)

6

]

z+

• L  [M(H 2

O)

5

L ]

z+

• H 2

O

[M(H

2

O)

5

L]

z+

• L  [M(H 2

O)

4

L

2

]

z+

• H 2

O

[M(H

2

O)

4

L

2

]

z+

• L  [M(H 2

O)

3

L

3

]

z+

• H 2

O

[M][L ] [ML ] K 1  [ML][L ] [ML ] K 2 2  [ML ][L ] [ML ] K 2 3 3 

M + L  ML M + 2 L  ML 2 M + 3 L  ML 3 M + n L  ML n Overall Stability Constants (  n )

[M][L ]

[ML ]

1

1 2 2 2 2

K K

[M][L ]

[ ML ]

1 2 3 3 3 3

K K K

[M][L ]

[ ML ]

n 1 2 n  K K K

Factors Affecting K f

1. Ligand Preference

 Dictated largely by HSAB & Metal Ox. St.

 (^) Hard Acids (Fe3+, V3+, Mn3+)  (^) Hard Bases (RO  , NR 3

 (^) Soft Acids (Au+, Cu+, Hg+)  (^) Soft Bases (RS  , PR 3

2. Coordination Geometry

 (^) Does metal prefer 2, 3, 4, 5, 6, 7, or 8

Factors Affecting K f

3. Chelate Effect

 Polydentate ligands  stability of Metal

complex over monodentate ligands ( K

f

 (^) Once one site bound, other(s) in close proximity  (^)  most favorable to add  (^) Most Biochemical Metal Binding sites are chelating ligands  (^) Can stabilize even labile metals  (^) K= 10^12 – 10^25

Factors Affecting K f : 3. Chelate  (^)  G  =  H   T  S   (^) Contributions from both enthalpy & entropy  (^) Entropy easier to understand [Ni(OH 2 ) 6 ] 2+ ( aq ) + 6NH 3 ( aq )  [Ni(NH 3 ) 6 ] 2+ ( aq ) + 6H 2 O( aq ) 7 complex ions/molecules 7 complex ions/molecules  (^)  S   0 [Ni(NH 3 ) 6 ] 2+ ( aq ) + 3en( aq )  [Ni(en) 3 ] 2+ ( aq ) + 6NH 3 ( aq ) 4 complex ions/molecules 7 complex

Macrocyclic Ligands  (^) Take chelate effect to next level N N C C C C O O O O  O  O O  O  N NH HN N Corrin Ring EDTA (^4)  N N (^) N N 2  porphyrin O O O O O O 18-crown-6-ether M M M

In Class Exercises

 Given the following data

Ag

( aq ) + 2NH 3

( aq )  [Ag(NH

3

2

]

( aq ) log K = 7. Ag

( aq ) + Br

• ( aq )  AgBr( s ) log K = 12.

 Calculate

1. Ksp for AgBr
2. K for the reaction [Ag(NH 3

2

]

( aq ) + Br

• ( aq )  AgBr( s ) + 2NH 3 ( aq )

Coordination Complexes

Coordination Complexes

 Central metal atom surrounded by set of

ligands.

 (^) Complex ion: [Co(NH 3 ) 6 ] 3+ , [PtCl 4 ] 2   (^) Compound: Ni(CO) 4

Primary coordination sphere

 Set of ligands directly attached to central

metal ion by coordinate covalent bonds

Outer Coordination Sphere

 Complex ions electrostatically (ionicly)

 Associated with counterion

 (^) there to balance charge only

 Without displacing ligands already present

Complex ion Counterion Outer sphere Complex [Mn(OH 2

6

]

2+

• SO 4 2  = [Mn(OH 2

6

](SO

4

[Co(NH 3

6

]

3+

• 3 Cl  = [Co(NH 3

6 ]Cl 3 [PtCl 4

]

2 

• 2 Na

= Na 2 [PtCl 4

]

IUPAC Nomenclature for

Coordination Complexes

1. Name coordination complex ion or

neutral coordination compound with no

spaces

 (^) For ionic complexes name  (^) Cation first, anion second  (^) Put space between names of complex ion & counterion