18 electron rule

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1.The number of metal-metal bond in [W2(OPh)6] is
    A.1
    B.2
    C.3
    D.4



Answer:- Option C

*18 Electron rule  :-The 18 electron rule follows the transition metal with some exception.
there are two types for 18 electron calculation.
1.By the oxidation state method :-
2.By the Neutral atom method:-

eg.Fe(CO)5 = 8+2x5=18 electron
CH3Mn(CO)5 =1+7(5x2)=18 electron............( all alkyls groups contribute 1 electron)
η5CpFe(CO)2Cl=5+8+4+1=18 electron
[CpCO]+=2X5+9-1=18 electron.....................(If complex has +ve charge on it, it is substractes during calculation.If complex has -ve charge that it is added during calculation.)

The complex viz follows 18 electron rule are stable and diamagnetic in nature ...and the complex viz follows 17 electron rule are strong oxidizing agent and paramagnetic behavier.

The complex viz follows 19 electron rule are strong reducing agent and paramagnetic behavier.

Question:-[W(Cp2)(CO)2] this compound follow 18 electron rule so what is the hapticity of Cp?
Ans:-6+2Cp+(2x2)=18
         10+2Cp=18
          2Cp=18
        Cp=5,Cp=3
question :-find the unknown values [MnBr(CO)n]
Ans:-7+1+2n=18
             2n=18-8
             2n=10
               n=5

*  Calculation of metal-metal bond.....
 Step 1.A=determine the total valance electrons.
Step 2.B=(nx18)-A........n=number of metal in the given cluster.
Step 3.B/2=gives total no. of metal- metal bonds.
Step 4.A/n=gives the no. of electron per metal bond.
if -1. no. of electron=18.......no per M-M bond.
     2.no. of electron=17.......1 per M-M bond.
     3.no. of electron=16........2 per M-M bond.
     4.no.of electron=15.........3 per M-m bond.

eg.[Fe2(CO)9]
1.TVE=A=8x2+9x2=34
2.B=nx18-A=2x18-34=2
3.B/2=2/2=1=one M-M bond
4.A/n=34/2=17 one per M-M bond

eg.(CO)2Rh(μ-Cl)2Rh(CO)2
1.TVE=A=4+9+3x2+9+4=32
2.B=nx18-A=2x18-32=4
3.B/2=4/2=2  two M-M bond
4.A/n=32/2=16 two per M-M bond

For square  planar complex:-
square planar complex follows 16 electron rule and are stable.....
1.TVE=A
2.B=nx16-A
3.B/2
4.A/n......16- No per M-m bond
                 15-one per M-M bond
                 14-two per M-M bond
                  13- three per M-M bond

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