Coordination Chemistry

Transition Metal Complexes 1. Also called simply as coordination compounds or complex compounds (During the initial stages of development, they were not obeying the valence rules and appeared unusual. unusual Therefore the name complex compounds)

2. They are the compounds that contain transition metal atoms or ions bonded to one or more ligands

3 An 3. A example l off a coordination di ti compound d is i shown h b l below:

Coordination Compounds: A Brief Summary 1. Most of them are colored and show interesting magnetic and optical properties

2. They find applications in various fields and are used as pigments, catalysts, model compounds in biological systems, etc.

3 Various 3. V i classifications l ifi ti are possible: ibl (a) ( ) The Th chemistry h i t off compounds d that th t posses metal-carbon bond(s) called as organometallics. (b) Inorganic chemistry y of the coordination compounds p seen in biological g systems y called as bioinorganic chemistry

Transition Elements 1. One way to define a transition element is, either the element or its cation contains incompletely filled d sub-shell

Important Properties of Transition Elements 1. They are metals and are hard and strong y 2. Form various alloys 3. Conduct heat and electricity 4. Almost all them have high melting and boiling points 5. They form ions in various formal oxidation states; most of the ions are colored and paramagnetic 6. They form compounds

coordination

compounds

and

organometallic

7. Transition metals and their compounds can show catalytic activity

Ligands 1. Ligands are the neutral molecules or anions that form bonds with the central metal atom or ions 2. They are classified in various ways based on (a) the number of electrons donated to the metal center (b) the charge on them (c) the type yp of binding g atom(s) ( )p present in them and ((d)) their size 3. Denticity defines the number of lone pairs of electrons donated by a ligand to the metal center. center Thus monodentate [monos(Greek) and dentis(Latin) = one tooth], bidentate, and tridentate ligands donate one, two, and three lone pair(s) of electrons to the metal atom or ion,, respectively. p y 4. Except the monodentate ligands others can be called generally as multidentate or polydendate ligands. ligands

Neutral Monodentate and Multidentate Ligands 1. Neutral Monodentate ligands: NH3 (ammine), H2O (aqua), C5H5N (pyridine), etc.

2. Neutral bidentate ligands:

H 2N

CH 2

CH2

NH 2

H2N

NH 2 M

Et hylenedi amine ( en)

When multidentate ligands form one or more rings with metal center they are termed as chelates or chelating agents [Chele(Greek) = claw]

Neutral Multidentate Ligands 3. Example of a Neutral tridentate ligand is shown below:

H N

NH 2

H2 N

Diethy lenetri ami ne ( dien)

Anionic Monodentate and Multidentate Ligands 1. Anionic Monodentate ligands: F- (fluoro), Cl- (Chloro), Br- (bromo), I- (Iodo), NO3- (nitrato), etc. 2. Anionic bidentate ligands: O O

O C

O

C

C O

Oxal at o ( ox)

H2 N

O

M Gl yci nat o ( gly)

Anionic Multidentate Ligands 3 Example of an anionic tridentate ligand is shown below: 3.

O

O

N S

S

Py rid ine di thi ocarboxyl ato ( pdt c)

4. Example of a tetraanionic hexadentate ligand is shown below: O

O

C

C

O

O N

N

O

O C

C

O O Et hylenedi aminetetracetat o ( edta)

Anionic Multidentate Ligands 5 Example 5. E l off a diaanionic di i i tetradentate t t d t t ligand li d is i shown h b l below: Ph

NH

N

Ph

Ph N

HN

Ph Porphyri n

Werner Coordination Theory

Proposed his theory in 1892 and received the Noble Prize in chemistry in 1913 as the first inorganic chemist

Werner Coordination Theory

S. No. 1

Complex CoCl3⋅6NH3

Color Yellow

2

CoCl3⋅5NH3

Purple

3

CoCl3⋅4NH3

Green

4

CoCl3⋅4NH3

Violet

Name Luteo complex Purpureo complex Praseo complex Violeo complex

CoCl3 6 NH3 + ex AgNO3

3 AgCl (ppt)

CoCl3 5 NH3 + ex AgNO3

2 AgCl (ppt)

CoCl3 4 NH3 + ex AgNO3

1 AgCl (ppt)

Werner Coordination Theory 1. The single fixed valence idea will not work for cobalt and proposed that it should have two types of valence 2 Secondary valence (nabenvalenz) that is non-direction and ionizable. 2. ionizable Today we call it as the oxidation state 3. Primary valence (hauptvalenz) that is directional (oriented toward fixed geometric positions in space). Today we call it as the coordination number. Here the coordination number for cobalt is six. Cl

NH3

H 3N

NH3 NH 3

Co H3 N

Cl NH 3

Cl

NH3

H 3N Cl

Cl NH 3

Co

H3 N

Cl NH 3

Cl

H 3N

NH 3 Co

H3 N

Cl NH3

Cl

Werner Coordination Theory S.

Empirical formula of

Molar

Formula by

No.

the complex

conductivity

Werner

1

PtCl4⋅2NH3

3.52

[Pt(NH3)2Cl4]

Nature

nonelectrolyte

((trans)) 2

NaCl

123.7

---------

1:1 electrolyte

3

CaCl2

260 8 260.8

---------

1:2 electrolyte

4

CoCl3⋅5NH3

261.3

[Co(NH3)5Cl]Cl2

1:2 electrolyte

5

L Cl3 LaCl

393 5 393.5

---------

1 3 electrolyte 1:3 l t l t

6

CoCl3⋅6NH3

431.6

[Co(NH3)6]Cl3

1:3 electrolyte

Conductivities of Coordination Compounds

Werner Coordination Theory 1 1 6

1

2 3

5

2

M

M 5 4 Hexagonal Pl anar , A

M 3

2

4

4

3

5 6 T rigonal P rism, B

6 Octahedr al , C

S. No.

Formula of the complex

Predicted number of isomers for different geometries A B C 1 1 1

Isolated number of isomers

1

MA5B

2

MA4B2

3 (1,2), (1,3), and (1,4)

3 (1,2), (1,4), and (1,6)

2 (1,2) and (1,6)

2

3

MA3B3

3 (1,2,3), (1,2,4), and (1,3,5)

3 (1,2,3), (1,2,4), and (1,2,6)

2 (1,2,3) and (1,2,6)

2

1

S. No 1. 2.

Geometry Linear Trigonal Planar

C. N 2 3

Hybridization sp sp2

Orbitals s, p s,px, py

3.

Tetrahedral

4

sp3

s, px, py, pz

4.

Square planar

4

dsp2

dx2 - y2, s, px, py

5.

5

dsp3

dz2, s, px, py, pz

6.

Trigonal bipyramidal Square pyramidal

5

dsp3

dx2 - y2, s, px, py, O=V(acac)2, [Ni(CN)5]3-pz

7.

Octahedral

6

d2sp3 or sp3d2

dx2 - y2, dz2, s, px, py, pz

Example [Ag(NH3)2]+ [Cu(SPMe3)3+[ClO4]Tris(trimethylphosphin e sulfide)copper(I) perchlorate [Zn(NH3)4]2+ [[Fe(Br) ( )4]2[Pt(NH3)4]2+ , [Pt(NH3)2Cl2], [Ni(CN]2NiBr3(PEt3)2

[Co(NH3)6]3+

C N C.

Minimum radius

Coordination

ratio

geometry

4

0.225

Tetrahedron

6

0.414

Octahedron

8

0.732

Cube

No. of unpaired e -s

Spin only magnetic moment(μs) (BM)

1

1.73

2

2.83

3

3.87

4

.90 4.90

5

5.92

Crystal Field Theory (CFT)

Shapes of d-Orbitals

Shapes of d-Orbitals

Shapes of d-Orbitals

Shapes of d-Orbitals

Shapes of d-Orbitals