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Tuesday, August 6, 2019

SIDWICK THEORY AND EAN RULE:

According to Sidwick Central metal ion of coordination complex will continue accepting electron pairs till the total number of electrons in the metal ion and those donated by ligands is equal to that of the next higher noble gas. This total number of electrons is called effective atomic number (EAN) of the metal. However this rule is more valid for non classical complexes specially carbonyl compounds hence this rule used for determining Stoichiometry, stability. Oxidizing and reducing character of carbonyl compounds.
CALCULATION OF EAN:

Total number of electrons possessed by the central atom in a complex is called Effective Atomic Number (EAN).

EAN = Z-(OS) Oxidation State + 2*coordination Number
This is Not applicable for pi complex
EAN = Z-(OS) Oxidation State + Total Number of electrons gained from ligands


For fast calculations remember the atomic number of the noble gases which are given as

He
2

Ne
10

Ar
18

Kr
36
for 3d series metals
Xe
54
for 4d series metals
Rn
86
for 5d series metals

ILLUSTRATIVE EXAMPLES OF E.A.N. CALCULATION:

SN
COMPLEX
EAN CALCULATION
EAN
1
[Co(CO)4]-
27+1+ 4*2
36
2
[Fe(Co)(NO)3]+
26-1+2+3*3
36
3
[Mo(Co)(NO)3]
25-0+2+3*3
36
4
[Cr(Co)6]
24-0+2*6
36
5
[Fe(pi-(C5H5)2]0
26-2+2*6
36
6
[Cr(pi-(C6H6)2]0
24-0+2*6
36
6
[Ru(CO)5]
44-0+2*6
54
7
[V(CO)6]
23-0+2*6
35
8
[Ti(Sigma-C2H5)(pi-C5H5)]
22-4+2*2+2*6
34
9
[PtCl3(pi-C2H4)]
78-2+2*3+2
84
10
[Co(NH3)6]Cl3
27-3+2*6
36

IMPORTANT NOTE:

(1) The EAN rule is generally found to be not valid in case of most of the complexes but in case of metal carbonyls (which is an important class of complexes, we will be studying later) this rule is found to be valid in all cases except one or two exceptions, so do remember it for metal carbonyls and do know how to calculate the EAN for any metal.

(2) NO ligand is found to act as three electron donor, as indicated by the following reactions in which when the carbonyl compound is heated in atmosphere of excess of NO. But also remember that NO+ is only two electron donor

[Fe(CO)5] + 2NO à [Fe(CO)2(NO)2] + 3CO
[Cr(CO)6] + 4 NO à[Cr(NO)4] + 6 CO

EAN FOR POLYNUCLEAR CARBONYL:  

Only CO is the ligand which can act as bridge ligand which donates only one electron to the one central atom.

[Fe(CO)9] , [Fe3(CO)12] , [Co2(CO)8] , [Mn2(CO)10] , [Ru3(CO)12] , [Re2(CO)10]

Direct Shortcut method:
ILLUSTRATIVE EXAMPLE (1): Calculate EAN of Fe2(CO)9 and Ru3 (CO)12 ?
SOLUTION:
(A) Calculate of EAN of Fe2(CO)9  !

(B) Calculate of EAN of Ru3 (CO)12  !
USES OF EAN RULE: 

However this EAN rule is more valid for non classical complexes specially carbonyl compounds hence this rule used for determining Stoichiometry, stability. Oxidizing and reducing character of carbonyl compounds.

In general if a complex have EAN equal to the Atomic Number of one of the inert gas then complex is stable however exception is also there for example  EAN of [Fe(CN)6]4- is 36 while EAN of [Fe(CN)6]3- is 35 But [Fe(CN)6]3- is more stable than  [Fe(CN)6]4- due to more effective charge in Fe+3 .

1
[Fe(CN)6]4-
26-2+2*6
36
2
[Fe(CN)6]3-
26-3+2*6
35


ILLUSTRATIVE EXAMPLE (2): Find the  value of (x) in the following compounds

(1) [Co2(CO)x] 
(2) Hx[Mn(CO)5]  
(3) [Fe(CO)(NO)x]+ 
(4) Cr(CO)x

SOLUTION:

Such type of question we will always consider that EAN is valid,so  with help of EAN we will find x

SN
COMPLEX
EAN CALCULATION
EAN
Value of x
1
[Co2(CO)x]
27*2 +1*2+ 2*x
36
X=8
2
[Fe(CO)(NO)x]+
26-1+2+ 3*x
36
X=3
3
[H x Mn(CO)5]
25+x+2*5
36
X=1
4
[Cr(Co)x]
24-0+2*x
36
X=6

ILLUSTRATIVE EXAMPLE (2):  Assign the oxidizing and reducing character to the following compounds?  [V(CO)6] , [Fe(CO)2(NO)2] , [Mn(CO)5]+ and [Co(CO)4]2-

SOLUTION:

SN
COMPLEX
EAN
Nature of compounds
1
[V(CO)6]
35
Reducing agent
2
[Fe(CO)2(NO)2]
36
Oxidizing agent
3
[Mn(CO)5]+
34
Oxidizing agent
4
[Co(Co)4]2-
37
Reducing agent

Related questions:



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Monday, August 5, 2019

SPECIAL LIGANDS:

(1) Polydentate ligands : have Flexi dentate character, it is not necessary that all the donor atoms present in the Polydentate ligands should form coordinate bonds with central metal atom or ion.
(2) Ambidentate Ligands: Ligands which can ligate through two different atoms present in it are called Ambidentate ligands. Examples of such ligands are the NO2, and SCN ions. NO2 , ion can coordinate through either the nitrogen or the oxygen atoms to a central metal atom/ion. Similarly, SCN¯ ion can coordinate through the sulphur or nitrogen atom. There are certain ligands which have two or more donor atoms but during formation of complexes only one donor atom is attached to metal ion. Such ligands are called Ambidentate ligands such as CN¯, CNS¯
(3) Chelating ligands:
(1) Polydentate ligands whose structures permit the attachment of two or more donor sites to the same metal ion simultaneously, thus closing one or more rings are called chelating ligands and the compounds formed are known as chelate compounds.
(2) A chelate may be defined as a ring structure formed by the combination of a Polydentate ligand having two or more donor atoms with a metal ion forming part of the ring.
(3) The process of formation of chelates is called chelation.
(4) Chelate complexes are more stable than ordinary complexes in which the ligand is a monodentate
(5) This increased stability of the compound due to chelation is called the chelate effect
(6) In the complex ion given below, 5membered rings are formed. So all these are called chelate complexes
(9) Generally the chelate complexes with 5 or 6 membered rings are more stable.
(10) Out of these, 5 membered rings are very stable when they involve saturated ligands.
(11) On the other hand 6-membered ring structures acquire maximum stability when they involve unsaturated ligands containing conjugate double bond. This is due to the resonance effects involving metal d-orbitals and ligand p-orbital electrons.

IllUSTRATIVE EXAMPLE (1): Match the Column A and B
Column A

Column  B
(1)
Ligand contains one donor site
(a)
hexadented
(2)
Ligand contains two donor site
(b)
tridented
(3)
Ligand contain three donor site
( c)
tetradented
(4)
Ligand contain four donor site
(d)
bidented
(5)
Ligand contain six donor site
(e)
unidented

SOLUTION:  (1) - (e); (2) - (d); (3) - (b); (4) - (c); (5) - (a)
Kumar Sir at No comments:
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Wednesday, July 3, 2019

Structure of phosphorous trioxide (P4O6) and phosphorous pentaoxide (P4O10) :

Phosphorous is a pentavalent element hence show +3 and +5 oxidation state (d orbital presence).it form two oxide P2O3 (+3) and P2O5 (+5). These oxide of phosphorus exist as dimer in form of P4O6 (+3) and P4O5

Comparative Study of P4O6 and P4O10 :

SN
Properties
P4O6
P4O10
1
Hybridisation (P) atom
 Sp3
Sp3
2
Hybridisation (O) atom
Sp3
Sp3 /Sp2 of Vertex (O)
3
No of Bridge bond (P-O-P)
6
6
4
No of Six member ring
4
4
5
No of Total  (l.p.)
16
20
6
No of Back Bond
0
4
7
No of P(pi)-P(pi) Bond
0
0
8
No of 2P(pi)-3d(pi) Bond
0
4
9
Longer (P-O) Bond
All are equal
12
10
Shorter (P-O) Bond
All are equal
4
11
Bond Length (P-O)
166 pm (Longer)
145 pm (shorter)
12
Bond Angle (O-P-O)
99.5 =100 (smaller)
102 (bigger)
13
Bond Angle (P-O-P)
127 (bigger)
123 (smaller)
14
No of Sigma Bond
12
16
15
No of (Pi) Bond
0
4
16
No of oxygen atom attached with( P)
3
4

Common feature of P4O6 and P4O10 :

(1) Both oxides have closed cage like structure.
(2) Both oxides contain six (P-O-P) Bond.
(3) Both oxide have 4 six member ring.
(4) Both are the anhydride of their respective acids.
(5) Both are Non planer

Explanation of Different Bond length and Bond Angle In P4O6 and P4O10 :
(1) According to "Bent's rule" lone pair electron  prefer to Stay to in those atomic hybrid orbitals have more % s-character.
(2) In case of P4O6 molecules, atomic hybrid orbitals containing lone pair electrons have more (s) character and less (p) character hence shorter bond length while remaining orbitals have less (S) character and more (p) character hence longer bond length (X1) than (X2) in P4O10 .
(3) We know that On increasing % s character in hybrid orbital, the bond length decreases while bond angle increases.
(3) In Case of P4O6  (O-P-O) bond angle is smaller due to higher p-character in atomic hybrid orbitals than orbital containing (O-P-O) in P4O10. (have more s-character )
For reading more Details about  click on  Bent Rule and Drago’s rule 

Related Questions:

Which is more basic N(CH3)3 or N(SiH3)3 , explain?

Are all the five bonds of PCl5 equivalent? Justify your answer.

Trisilyl amine, N(SiH3)3 is planar whereas trimethyl amines N(CH3)3 is pyramidal. Explain why?.















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