Online Notes on "Coordination Compounds" (Chapter=>9 ) Part 2

These are Online Notes on "Coordination Compounds" (Chapter=>9 ) Part 2 for practice of CBSE BOARD, CBSE NEET, CSIR NET Chemical Sciences etc.

16.           Ambidentate  ligand:  Ligands  which  can  ligate  (link)                         

through  two different atoms present in it are called ambidentate ligand. 

Example: 

NO2-,and SCN-. NO2- can link through N as well as O while SCN- can  

link through S as well as N atom.

17.           Werner’s coordination theory: Werner was able to explain    the nature of bonding in complexes. The postulates of Werner’s theory  are:

a.    Metal shows two different kinds of valencies: primary valence and secondary valence.

Primary valence	Secondary valence
This valence is normally ionisable.	This valence is non – ionisable.
It is equal to positive charge on central metal atom.	The secondary valency equals the number of ligand atoms coordinated to the metal. It is also called coordination number of the metal.
These   valencies   are   satisfied   by negatively charged ions.	It is commonly satisfied by neutral and negatively charged, sometimes by positively charged ligands.
Example: in CrCl3, the primary valency is three. It is equal to oxidation state of central metal ion.

b.    The ions/ groups bound by secondary linkages to the metal  have characteristic spatial arrangements corresponding to different coordination numbers.

c.   The most common geometrical shapes in coordination compounds are octahedral, square planar and tetrahedral.

18. Oxidation number of central atom: The oxidation number of the central atom in a complex is defined as the charge it would carry if all the ligands are removed along with the electron pairs that are shared with the central atom.

19. Homoleptic complexes: Those complexes in which metal or ion is coordinate bonded to only one kind of donor atoms. For example: [Co(NH3)6]3+

           

           20. Heteroleptic  complexes:  Those complexes in which metal or ion  is

coordinate bonded to more than one kind of donor atoms. For example: [CoCl2(NH3)4]+, [Co(NH3)5Br]2+

          21.  Isomers. Two or more compounds which have same chemical                       formula but different arrangement of atoms are called isomers.

22. Types of isomerism:

a.    Structural isomerism

i.     Linkage isomerism

ii.     Solvate isomerism or hydrate isomerism

iii.     Ionisation isomerism

iv.    Coordination isomerism

b.    Stereoisomerism

i.     Geometrical isomerism

ii.     Optical isomerism

23. Structural isomerism: This type of isomerism arises due to the difference in structures of coordination compounds. Structural isomerism, or constitutional isomerism, is a form of  isomerism  in which molecules with the same molecular formula have atoms bonded together in different orders.

a.  Ionisation isomerism: This form of isomerism arises when the counter ion in a complex salt is itself a potential ligand and can displace a ligand which can then become the counter ion. Example: [Co(NH3)5Br] SO4 and [Co(NH3)5 SO4] Br

b.  Solvate isomerism: It is isomerism in which solvent is involved as

ligand. If solvent is water it is called hydrate isomerism, e.g., [Cr(H2O)6]Cl3   and [CrCl2(H2O)4] Cl2. 2H2O

c.    Linkage  isomerism:  Linkage isomerism arises in a   coordination

compound containing ambidentate ligand. In the isomerism, a ligand   can  form   linkage  with  metal  through  different   atoms.

Example: [Co(NH3)5ONO]Cl2 and [Co(NH3)5NO2]Cl2

d.   Coordination isomerism: This type of isomerism arises from the interchange of ligands between cationic and anionic entities of different metal ions present in a complex. Example: [Co(NH3)6][Cr(C2O4)3] and [Cr(NH3)6][Co(C2O4)3]

        24.  Stereoisomerism: This type of isomerism arises because of    different spatial arrangement.

a.    Geometrical isomerism: It arises in heteroleptic complexes due to different possible geometrical arrangements of ligands.

b.    Optical isomerism: Optical isomers are those isomers which are non superimposable mirror images.

           25. Valence bond theory:

According to this theory, the metal atom or ion under the influence of ligands can use its (n-1)d, ns, np or ns, np, nd orbitals for hybridisation

to yield a set of equivalent orbitals of definite geometry such as octahedral, tetrahedral, and square planar.

These hybridised orbitals are allowed to overlap with ligand orbitals that can donate electron pairs for bonding.

Coordination number	Type of hybridisation	Distribution of hybrid orbitals in space
4	sp3	tetrahedral
4	dsp2	Square planar
5	sp3d	Trigonal bipyramidal

6	sp3d2 (nd orbitals are involved – outer orbital complex or high spin or spin free complex)	Octahedral
6	d2sp3((n-1) d orbitals are involved –inner orbital or low spin or spin paired complex)	Octahedral

26. Magnetic properties of coordination compounds: A coordination compound is paramagnetic in nature if it has unpaired electrons and diamagnetic if all the electrons in the coordination compound are paired.

Magnetic  moment 

  


where  n  is  ber  of num   unpaired  electrons.

27. Crystal Field Theory: It assumes the ligands to be point charges and there is electrostatic force of attraction between ligands and metal atom or ion. It is theoretical assumption.

            28.        

	Crystal field splitting in octahedral coordination complexes:

29.           Crystal field splitting in tetrahedral coordination complexes:

20. For the same metal, the same ligands and metal-ligand distances, the difference in energy between eg and t2g  level is

4

Dt = -     D0

9

31. Metal carbonyls. Metal carbonyls are homoleptic complexes in which carbon monoxide (CO) acts as the ligand. For example: Ni(CO)4

The metal – carbon bond in metal carbonyls possesses both s and p

characters.

The metal-carbon bond in metal carbonyls possess both s and p character.
The M–C σ bond is formed by the donation of lone pair of electrons from the carbonyl carbon into a vacant orbital of the metal.

The M–C p bond is formed by the donation of a pair of electrons from a filled d orbital of metal into the vacant antibonding p* orbital of carbon monoxide.

The metal to ligand bonding creates a synergic  effect which strengthens the bond between CO and the metal.

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