Chapter 9 Coordination Compounds and Organometallics – Chemistry free study material by TEACHING CARE online tuition and coaching classes

 

 

When solutions of two or more stable compounds are mixed in stoichiometric (simple molecular) proportions new crystalline compounds called molecular or addition compounds are formed. These are of two types :

(1) Double salts, (2) Co-ordination or Complex compounds

• Double salts : Addition compounds, stable in solid Dissociate into ions in aqueous solution as such give test for each constituent ion. Examples:
• Co-ordination or Complex compounds : Addition compound, stable in solid Retain their identity even in solution. Central metal ion form dative or coordinate bond with the species surrounding it (ligands). Examples :

Complex compound	Cation	Anion
[Cu(NH3 )4 ]SO4	[Cu(NH3 )4 ]+2	SO2- 4
K 2 [PtF6 ]	2K +	[PtF6 ]2–
[Co (NH 3 )6 ][Cr (CN 3 )6 ]	[Co(NH 3 )6 ]2+	[Cr (CN)6 ]3–

• Central metal atom or ion : A complex ion contains a metal atom or ion known as the central metal atom or it is sometimes also called a nuclear atom.
• Complex ion : It is an electrically charged radical which is formed by the combination of a simple cation with one or more neutral molecules or simple anions or in some cases positive groups
• Ligands : Neutral molecules or ions that attach to central metal ion are called ligands. The donor atom associated with the ligands supplies lone pair of electrons to the central metal atom (forming dative bond) may be one or two Monodentate (one donor atom), bidentate (two donor atom), tridenatate (three donor atom) etc.

Monodentate Ligands (with one donor site)

Anionic Ligands (Negative legands)

Formula	Name	Formula	Name
X –	Halo	O 2- 2 CH 3 COO – NO – 3 S2 O2- 3 NO – 2 CO 2- 3 SO2- 4	Peroxo
: OH –	Hydroxo		Acetato
CN –	Cyano		Nitrato
O 2-	Oxo		Thiosulphato
NH – 2	Amido		Nitrito
S 2-	Sulphido		Carbonato
CNS –	Thiocyanato		Sulphato

Neutral Ligands

Formula	Name	Formula	Name
CO	Carbonyl	: NH 3	Amminato
PH 3 NO	Phosphine Nitrosyl	H 2 O C6 H5 N :	Aqua Pyridine (py)

 

 

 

Cationic Ligand (Positive)

Formula	Name	Formula	Name
NO + 2 H 2 NNH + 3	Nitronium Hydrazinium	NO +	Nitrosonium

Polydentate ligands (with two or more donor site)

Bidentate (Two donor sites)

Formula	Name	Formula	Name
H 2 NCH 2 CH 2 NH 2   O O –      ||    ||        – O– C– C– O	Ethylenediamine (en)	Me – C = NO – | Me – C = NOH	Dimethylglyoximeto (dmg)
	Oxalato (ox)	NH 2 – CH 2 – COO –	Glycinate ion (gly)

Chelating Ligand : When polydentate ligands bind to the central metal ion they form a ring called chelate and the ligand is referred as chelating ligand.

Ambidentate ligands : A ligand which possesses two donor atom but in forming complex it utilizes only one atom depending upon the condition and type of complex.

NO₂ (nitro) , ONO (nitrito), CN (cyano), NC (isocyano), SCN (thiocyanide), NCS (isothiocyanide)

p– acid ligand : Ligands which are capable of accepting an appreciable amount of p- e^– density from the

 

metal atom into emptying p or p ^*

orbital or their own called p –

acceptor or p –

acid ligands eg. CO.

 

• Co-ordination Sphere : Ligand with central metal ion is kept in square bracket [ ] retains its identity in the same form is called co-ordination sphere (non-ionisable)
• Co – ordination Number : Number of monodentate ligands attached to central atom/ ion are called coordination number of the central metal atom/ion.
• Ionisation Sphere : The part present out side of the square bracket is called ionization sphere (ionisable).

In order to name complex compounds certain rules have been framed by IUPAC. These are as follows :

• The positive part of a coordination compound is named first and is followed by the name of negative part.

 

 

 

• The ligands are named first followed by the central The prefixes di-, tri-, tetra-, etc., are used to indicate the number of each kind of ligand present. The prefixes bis (two ligands), tris (three ligands), etc., are used when the ligands includes a number e.g., dipyridyl, bis (ethylenediamine).
• In polynuclear complexes, the bridging group is indicated in the formula of the complex by separating it from the rest of the complex by In polynuclear complexes (a complex with two or more metal atoms), bridging ligand (which links two metal atoms) is denoted by the prefix m before its name.
• Naming of ligands : The different types of ligands i.e. neutral, negative or positive are named differently in a complex

When a complex species has negative charge, the name of the central metal ends in – ate. For some elements, the ion name is based on the Latin name of the metal (for example, argentate for silver). Some such latin names used (with the suffix – ate) are given below :

Fe	Ferrate	Cu	Cuperate
Ag Sn	Argentate Stannate	Au Pb	Aurate Plumbate

• Point of attachment in case unidentate ligands with more than co-ordinating atoms (ambidentate ligands) : The point of attachment in case of unidentate ligands with more than one co-ordinating atoms is either indicated by using different names for the ligands (e.g, thiocyanato and isothiocyanato) or by placing the symbol of the donor atom attached, the name of the ligand separated by a hypen.

 

(NH ₄ )₃ [Cr(SCN)₆ ]

Ammonium hexathioxyanato -S-chromate (III) or

Ammonium hexathiocyanatochromate (III)

(NH ₄ )₂[Pt(NCS)₆ ]

Ammonium hexathiocyanato -N- platinate (IV) or

Ammonium hexaisothiocyanatoplatinate (IV)

 

• Name of the bridging groups : If a complex contains two or more central metal atoms or ions, it is termed as polynuclear. In certain polynuclear complexes. ligands may link the two metal atoms or ions. Such ligands which link the two metal atoms or ions in polynuclear complexes are termed as bridge ligands. These bridge ligands are separated from the rest of the complex by hyphens and denoted by the prefix m . If there are two or

more bridging groups of the same kind, this is indicated by di– m -, tri –m -, etc.

 

[(NH 3 )]5 Co – NH 2 – Co(NH 3 )5 ](NO3 )5 ;

m -amidobis [pentaamminecobalt (III)] nitrate

 

[(CO)3 Fe(CO)3 Fe(CO)3 ]

tri- m carbonylbis [tricarbonyliron (0)]

[(NH 3 )5 Co – OH – Co(NH 3 )5 ]Cl5

m – hydroxobis [pentaamminecobalt (III) ] chloride

 

[Be₄O(CH₃COO)₆]

hexa – m -acetato(O,O’)- m₄oxotetraberyllium(II )

 

• If any lattice component such as water or solvent of crystallisation are present, these follow the name and are preceded by the number of these groups (molecules of solvent of crystallisation) in Arabic

For example,

 

[Cu(H2O)4 ]SO4 .H2O

Tetraaquacopper(II)sulphate1-water

[Cr(H2O)4  Cl2 ]Cl.2H2O

tetraaquadichlorochromium (III( chloride 2- water

 

• Following punctuation rules should also be followed while writing the name of the complex

 

• The name of the complete compound should not start a capital letter, g.,

[Cu(NH3 )4 ]SO4

Tetraamminecopper (II) sulphate (Correct) Tetraamminecopper (II) sulphate (Incorrect)

 

• The full name of the complex ion should be written as one word without any

 

 

 

• There should be a gap between the cation and anion in case of ionic

• The full name of non-ionic complexes should be written as one word without any gap.

Compounds having the same molecular formula but different structures or spatial arrangements are called isomers and the phenomenon is referred as isomerism.

• Structural isomerism : Here the isomers have different arrangement of ligands around the central metal It is of the following types :
  • Ionisation isomerism : The co-ordination compound having the same composition or molecular formula but gives different ions in solution are called ionization

There is exchange of anions between the co-ordination sphere and ionization sphere.

Example : [Co Br (NH 3 )5 ] SO4                                                        [Co SO4 (NH 3 )5 ] Br

Pentaaminebromo cobalt (III) Sulphate               Pentaaminesulphato cobalt (III) bromide

 

4

SO ^2– present in ionisation sphere

Br ^–

present in ionization sphere

 

Gives white precipitate with BaCl ₂

Gives light yellow precipitate with

AgNO3

 

• Co-ordination isomerism : In this case compound is made up of cation and anion and the isomerism arises due to interchange of ligands between complex cation and complex

Example : [Co(NH 3 )6 ] [Cr (CN)6 ]                                                 [Cr (NH 3 )6 ][Co(CN)6 ]

hexaamine cobalt (III) hexacyano chromate (III) hexaamine chromium (III) hexacyanocobalt (III)

 

complex cation contains ® NH ₃ ligand (with cobalt)          complex  anion   contains     ® NH 3

chromium)

complex anion contains ® CN ^– ligand (with chromium)               complex anion contains ® CN ^–

cobalt)

ligand   (with ligand (with

 

• Linkage isomerism : In this case isomers differ in the mode of attachment of ligand to central metal ion

and the phenomenon is called linkage isomerism.

 

Example : [Co ONO (NH 3 )5 ]Cl2

[Co NO2 (NH3 )5 ]Cl2

 

2

Pentaamminenitritocobalt (III)                                       Pentaaminenitrocobalt (III) chloride

 

: O – NO ^– oxygen atom donates lone pair of electrons (nitrito) electrons (nitro)

NO ^–

nitrogen atom donates lone pair of

 

• Hydrate isomerism : Hydrate isomers have the same composition but differ in the number of water

molecules present as ligands and the phenomenon is called hydrate isomerism.

 

Examples :(i) [Cr (H 2 O)6 ] Cl3

hexaaquachromium (III) chloride (violet)

 

(ii) [Cr (H ₂O)₅ Cl ] Cl₂ . H ₂O pentaaquachlorochromium (III) chloride monohydrate (blue green)

(iii) [Cr (H 2 O)4 Cl ] Cl2 . 2H 2 O tetraaquadichlorochromium (III) chloride dihydrate (green)

• Stereo isomerism or space isomerism : Here the isomers differ only in the spatial arrangement of atoms of groups about the central metal It is of two types :
  • Geometrical or Cis-trans isomerism : This isomerism arises due to the difference in geometrical arrangement of the ligands around the central atom. When identical ligands occupy positions opposite to each other called cis-isomer. When identical

 

 

 

ligands occupy positions opposite to each other called trans –isomer. It is very common in disubstituted complexes with co-ordination number of 4 and 6.

Complexes of co-ordination number 4

Tetrahedral geometry : In this case all the four ligands are symmetrically arranged with respect to one another as such geometrical isomerism is not possible.

Square planar geometry : The four ligands occupy position at the four corners and the metal atom or ion is at the center and lie in the same plane.

Type : I [Ma2b2 ] , M = Pt, a = Cl, b = NH3

Example : [Pt Cl (NH 3 )(Py)2 ]

Note : ® Square planar complexes of types

 

Ma4 , Ma3 b,

Mab3

do not exhibit geometrical

 

isomerism as all the spatial arrangements of the ligands relative to each other are equivalent.

Complexes of co-ordination number 6

Octahedral geometry : Here the metal atom or ion lies at the center and 1 to 6 position are occupied by the ligands.

Cis–Positions : 1–2, 2–3, 3–4, 4–5

Trans – position : 1–4, 2–5, 3–6

 

 

 

 

Type –I

Ma4 b2 ,

M = Co, a = NH ₃ , and b = Cl

 

Example : [CoCl2 ( NH 3 )4 ]⁺ ion

 

 

Type –II [Ma₃b₃ ] , M = Rh, a = Cl, and b = Py

Example : [Rh Cl₃ (Py)₃

 

 

Type –III [M(aa)2 (en)2 ]⁺⁺ ,

 

• Optical isomerism

M = Co, a – a =

CH 2 NH 2

|

CH 2 NH 2

(bidentate), b = Cl

(monodentate)

 

• Optical isomers are mirror images of each other and have chiral
• Mirror images are not super imposable and do and have the plane of symmetry.
• Optical isomers have similar physical and chemical properties but differ in rotating the plane of plane polarized
• Isomer which rotates the plane polarized light to the right is called dextro rotatory (d-form) and the isomer which rotates the plane polarized light to the left is called laevorotatory (l–form)

 

 

 

 

 

Example : (a)

+

–

[Ma b c ]ⁿ ; [Pt(Py) (NH ) Cl ]²⁺

 

2 2 2                       2          3 2     2

 

• [M abc d e f ]; Pt (py) NH 3 NO2 Cl Br]

 

 

 

 

 

 

 

 

 

 

(c) [M(AA)3 ]^n± ;[CO(en)3 ]³⁺

(d) [M(AA)2 a2 ]^n± ;[Co(en)2 Cl2 ]⁺                                   (e) [M(AA)2 ab]^n± ; [Co(en)2 NH3 Cl]²⁺

 

 

 

Werner was able to explain the bonding in complex.

Primary valency (Pv) : This is non- directional and ionizable. In fact it is the positive charge on the metal ion.

Secondary valency (Sv) : This is directional and non- ionizable. It is equal to the number of ligand atoms co-ordinated to the metal (co-ordination number).

Example : [Co (NH 3 )6 ]Cl3	or	Co(NH 3 )6 ]3+ 3Cl –
Pv ® 3Cl – [3]                                Sv         ® 6 NH 3 (6) [Co(NH 3 )5 Cl]Cl2                                      or          [Co(NH 3 )5 Cl]2+ 2Cl – Pv ® 2Cl – (2)                                 Sv         ® 5 NH 3 + 1Cl – (6) [Co(NH 3 )4 Cl2 ] Cl                                     or          [Co(NH 3 )4 Cl2 ]+ Cl – Pv ® Cl – (1)                                   Sv         ® 4 NH 3 + 2Cl – (6)

 

Nature of the complex can be understood by treating the above complexes with excess of

CoCl3 . 6 NH 3 ® 3 AgCl, [Co(NH 3 )6 Cl3 (three chloride ion)

CoCl3 . 5 NH 3 ® 2AgCl, [Co(NH 3 )5 Cl2 (two chloride ion)

CoCl3 . 4 NH 3 ® 1AgCl, [Co(NH 3 )4 Cl2 (one chloride ion)

CoCl3 . 3NH 3 ® no AgCl, [Co(NH 3 )3 Cl3 (no chloride ion)

AgNO3 .

 

The nature of bonding between central metal atom and ligands in the coordination sphere has been explained by the three well-known theories. These are :

(1)  Valence Bond theory of coordination compounds

• The suitable number of atomic orbitals of central metal ion (s,p,d) hybridise to provide empty hybrid
• These hybrid orbitals accept lone pair of electrons from the ligands and are directed towards the ligand positions according to the geometry of the
• When inner d-orbitals e. (n-1) d orbitals are used in hybridization, the complex is called – inner orbital

or spin or hyperligated complex.

• A substance which do not contain any unpaired electron is not attracted by 2 It is said to be diamagnetic. On the other hand, a substance which contains one or more unpaired electrons in the electrons in the

 

d-orbitals, is attracted by a magnetic field [exception O₂

and NO]. It is said to be paramagnetic.

 

Paramagnetism can be calculated by the expression,

m _s =

where m = magnetic moment.

 

s= spin only value and n= number of unpaired electrons.

 

Hence, if n = 1, m _s =

= 1.73 B.M. , if n = 3, m _s =

= 3.87 B.M. and so on

 

On the basis of value of magnetic moment, we can predict the number of unpaired electrons present in the complex. If we know the number of unpaired electrons in the metal complex, then it is possible to predict the geometry of the complex species.

• There are two types of ligands namely strong field and weak field A strong field ligand is capable of forcing the electrons of the metal atom/ion to pair up (if required). Pairing is done only to the extent which is required to cause the hybridization possible for that Co-ordination number. A weak field ligand is incapable of making the electrons of the metal atom/ ion to pair up.

3

4

Strong field ligands : CN ^– , CO, en, NH 3 , H 2 O, NO^– , Py .

 

Weak field ligands :

I ^– , Br ^– , Cl ^– , F ^– , NO^– , OH ^– , C2

O^2– , NH 3

, H 2 O .

 

 

 

Geometry (shape) and magnetic nature of some of the complexes (Application of valence bond theory)

 

 

 

 

 

 

 

• Ligand field theory : According to this theory when the ligands come closer to metal atom or ion, a field is created. This field tends to split the degenerate d-orbitals of the metal atom into different energy levels. The nature and number and number of lignads determine the extent of splitting on the basis of which the magnetic and spectroscopic properties of the complex can be

Stronger is the metal-ligand bond, less is the dissociation in the solution and hence greater is the stability of a coordination compounds.

Instability constant for the complex ion [Cu(NH3 )4 ]²⁺ i.e.

 

 

[Cu(NH

) ]2+

⇌ Cu²⁺ + 4 NH

, is given by the expression;

K   = [Cu²⁺ ][NH3 ]⁴ .

 

3 4                                        3

ⁱ      [Cu(NH

3 )4 ]2+

 

Stability constant of the above complex i.e.

[Cu(NH )²⁺ ] 4       1

 

Cu²⁺ + 4 NH 3 ⇌ [Cu(NH 3 )²⁺ is given as under ;

K =            3 4         =

[Cu²⁺ ][NH 3 ]     K,

 

Greater is the stability constant, stronger is the metal – ligand bond

Factors affecting the stability of complex ion

• Nature of central metal ion : The higher the charge density on the central metal ion the greater is the stability of the complex

For example, the stability constant of [Fe(CN)6 ]^3– is much greater than the stability constant of [Fe(CN)₆]^4–.

Fe ²⁺ + 6CN ^–  [Fe (C N)6 ]^4– ; K = 1.8 ´ 10⁶

Fe ³⁺ + 6CN ^–  [Fe (C N)6 ]^3– ; K = 1.2 ´ 10³¹

Effective atomic number (EAN) or Sidgwick theory : In order to the stability of the complexes sidgwick proposed effective atomic number. EAN generally coincides with the atomic number of next noble gas in some cases. EAN is calculated by the following relation :

 

EAN = Atomic no. of the metal – e ^–

ligands.

lost in ion formation +No. of e ^–

gained from the donor atom of the

 

EAN = Atomic number – Oxidation number + co-ordination no. ´ 2

 

 

Complex	Metal oxidation state	At. No. of metal		Coordination number	Effective atomic number
K 4[Fe (CN )6 ]	+ 2	26	6	(26 – 2) + (6 ´ 2) = 36 [Kr]
[Cu (NH 3 )4 ]SO 4	+ 2	29	4	(29 – 2) + (4 ´ 2) = 35
[Co (CH 3 )6 ]Cl 3	+ 3	27	6	(27 – 3) + (6 ´ 2) = 36 [Kr]
Ni (CO )4	0	28	4	(28 – 0) + (4 ´ 2) = 36 [Kr]
K 2[Ni (CN )4 ]	+ 2	28	4	(28 – 2) + (4 ´ 2) = 34

 

 

 

K 2 [PtCl6 ]	+ 4	78	6	(78 – 4) + (6 ´ 2) = 86 [Rn]
K 3 [Cr (C 2O 4 )3 ]	+ 3	24	6	(24 – 3) + (6 ´ 2) = 33
K 3[Fe (CN )6 ]	+ 3	26	6	(26 – 3) + (6 ´ 2) = 35
K 2 [HgI 4 ]	+ 2	80	4	(80 – 2) + (4 ´ 2) = 86 [Rn]
[Ag NH 3 )2 ]Cl	+ 1	47	2	(47 – 1) + (2 ´ 2) = 50
K 2 [PdCl 4 ]	+ 2	46	4	(46 – 2) + (4 ´ 2) = 52

 

• Nature of ligand : Greater the base strength is the ease with which it can donate its lone pair of electrons and therefore, greater is the stability of the complex formed by

For example : [Cu(NH 3 )4 ]²⁺ ; K = 4.5 ´ 10¹¹ ; [Cu(CN)4 ]^2– ; K = 2.0 ´ 10²⁷

• Presence of chelate ring : Chelating ligands form more stable complex as compared to monodentate

 

ligands. For example :

Ni ²⁺ + 6 NH 3  [Ni(NH 3 )6 ]²⁺ ; K = 6 ´ 10⁸ ;

Ni ²⁺ + 3en  [Ni(en)3 ]²⁺ ; K = 4 ´ 10⁸

 

Spectro chemical series : Ligands can be arranged in increasing order of their strength (ability to cause crystal field splitting) and the series so obtained is called as spectro chemical series.

2

I ^– < Br ^– < Cl ^– < F ^– < OH ^– < OX ^2– < H 2O < Py < NH 3 < en < NO ^– < CN ^– < CO .

 

Ligands arranged left to

NH 3

are generally regarded as weaker ligands which can not cause forcible pairing

 

of electrons within 3d level and thus form outer orbital octahedral complexes.

 

On the other hand

NH 3

and all ligands lying right to it are stronger ligands which form inner orbital

 

octahedral complexes after forcible pairing of electrons within 3d level.

(1) Preparation : Coordination compounds are generally prepared by the application of the following methods,

• Ligand substitution reaction : A reaction involving the replacement of the ligands attached to the central metal ion in the complex by other ligands is called a ligand substitution

[Cu(H 2 O)4 ]2+ (aq) + 3NH 3 (aq)) ® [Cu(NH 3 )4 ]2+ (aq)

 

Light blue

 

 

• Direct mixing of reagent :

Deep blue

+4 H2O(l)

PtCl2 + 2H 2 N – CH 2 – CH 2 – NH 2  ®

(en)

 

[Pt(en)₂ Cl₂ ]

(Dichloro bis

(ethylene diam mine platinum (II)

 

 

• Redox reactions : In these reactions, either oxidation or reduction is involved

 

2CO(NO3 )2  + 8 NH 3  + 2NH 4 NO3  + H 2 O2

 

Application

2[CO(NH 3 )NO2 ](NO3 )2 + 2H 2 O

Penta ammine nitrocobalt (II) nitrate.

 

 

 

 

• Estimation of hardness in water, as Ca ⁺⁺

and

 

Mg 2+

ions form complexes with EDTA.

 

• Animal and plant world e.g. chlorophyll is a complex of vitamin B12 is a complex of Co ²⁺ .

Mg 2+

and haemoglobin is a complex of

Fe 2+

 

• Electroplating of metals involves the use of complex salt as electrolytes g. K [Ag (CN )₂ ] in silver plating.
• Extraction of metals g. Ag and Au are extracted from ores by dissolving in NaCN to form complexes.
• Estimation and detection of metal ions g. Ni ²⁺ ion is estimated using dimethyl glyoxime.

• Medicines e.g. cis-platin e. cis [PtCl2 (NH 3 )2 ] is used in treatment of cancer.

These are the compounds in which a metal atom or a metalloid (Ge, Sb) or a non-metal atom like B, Si, P, etc, (less electronegative than C) is directly linked to a carbon atom of a hydrocarbon radical or molecule. Organometallic compounds contain at least one..

(1) Metal – Carbon bond, (2) Metalloid – Carbon bond, (3) Non metal – Carbon bond. Example :

 

Compounds :

C2 H5 MgBr ,

(C2H5 )2 Zn ,

C6 H5 Ti(OC3 H7 )3 ,

(CH 3 )4 Si

 

Organometallic bond :

Mg – C ,

Zn – C ,

Ti – C ,

Si – C

 

Note : ®

bond.

B(OCH 3 )3 , (C3 H7 O)4  Ti

cannot be regarded as organometallics as there is not metal carbon

 

Classification of organometallic compounds : Organometallics have been classified as :

• s–bonded organometallic compounds : Compounds such as

 

RMgX, R2 Zn, R3 Pb, R3 Al, R4 Sn

etc, contains

M – C s –

bond and are

 

called s – bonded organometallic compound.

• p-bonded organometallic compounds : The transition metals binds to unsaturated hydrocarbons and their derivatives using their d- Here metal atom is bonded to ligands in such a way that donations of electrons and back acceptance by the ligand is feassible. These are called

p – orbitals of the ligand. These are called p complexes.

Examples : (i) p – cyclopentadienyl – iron complex

Ferrocene [Fe (h⁵ – CH5 )2] , Bis (cyclopentadienyl) iron (II)

It is a p bonded sandwitch compound. The number of carbon atoms

 

bonded to the metal ion is indicated by superscript on eta (h ^x ) i.e. h ⁵

(ii)  Dibenzene chromium ( p – complex)

in this complex.

 

 

Ferrocene

 

 

Dibenzene

 

It is also a p – bonded sandwitch compound. Its formula is [Cr(h ⁶ – C6 H6 )2 ]

(iii) Alkene complex ( p – complex)

Fe(h ⁵ – C5 H

5 )2

chromium

Cr(h ⁶ – C6 H6 )

 

Zeise’s salt K

Pt Cl3 (h ² – C2 H 4 )] ; Potassium trichloroethylene platinate (IV).

 

It is a p bonded complex. m ² indicates that two carbons of ehylene are bonded to metals.

 

 

 

• Complexes containing both s– and p– bonding characteristics : Metal carbonyls, compounds formed between metal and carbon monoxide belong to this class. Metal carbonyls have been included in
  • Mononuclear carbonyls : Contain one metallic atom per e.g Ni (CO)₄, Fe(CO)₅, Cr(CO)₆

 

• Polynuclear carbonyls : Contain two or more metallic atoms per e.g.,

Mn2 (CO)10 , Fe(CO)9 , Fe(CO)12

Applications of organometallics

• Grignard reagent (RMgX) has been extensively used for synthesis of various organic

 

 

• Wilkinson’s catalyst

[(PH ₃ P)₃ RhCl]

i.e. tris (triphenylphosphine) chlororhodium (I) is used as a

 

homogeneous catalyst for the hydrogenation of alkenes.

• Zeigler Natta catalyst (composed of a transition metal salt, generally used as heterogeneous catalysts in the polymerisation of

TiCl4

 

and trialkyl aluminium) are

 

 

• Flexidentate character : Polydentate ligands are said to have flexidentate character if they do not use all its donor atoms to get coordinated to the metal ion g. EDTA generally act as a hecadentate ligand but it can also act as a pentadentate and tetradentate ligand.
• Badecker reaction : This reaction involves the following chemical

Na2 [Fe(CN)5 NO] + Na2 SO3   ® Na4 [Fe(CN)5 (NO. SO3 )]

 

• Everitt’s salt : It is

K ₂[Fe(CN)₆ ] obtained by reduction of prussian blue.

 

 

• Masking : Masking is the process in which a substance without physical separation of it is so transformed

that is does not enter into a particular reaction e.g., masking of Cu ²⁺ by CN ^– ion.

• Macrocyclic effect : This term refers to the greater thermodynamic stability of a complex with a cyclic

 

polydentate ligand when compared to the complex formed with a non-cyclic ligand. e.g., ligand;

Zn(II)

complex with

 

• Prussian blue and Turnbull’s blue is pot. ferric ferrocyanide. However colour of Turnbull’s blue is less intense than prussian blue. Decrease in colour is due to the presence in it of a white compound of the formula K ₂ {Fe[Fe(CN)₆ ]} named as potassium ferrous