Streamlining the Organometallic compounds

Stability of the transition metal complex:

Elements tend to achieve the stability by making low energy compounds. Organometallic compounds are the same. They are stable because they are lesser in energy with compared to their individual forms. Scientists found that most of these metal complexes have 18 electrons in the metal valence shell. 

Application of the 18 electrons rule

**lets simplify the 18 e rule**

1 step: Count the number of electrons in the valence shell of the metal

2 step: get the dⁿ configuration

3 step: count the total number of electrons donate by the ligands

4 step: make corrections for the charge

**Here is an example to make this easier to understand**

Example 01;  Fe(CO)5 

Step 1; Iron belongs to the d block of the periodic table. [Ar]3d64s2

Step 2; dⁿ configuration = d⁸

Step 3; Each carbonyl donates 2 electrons. 2*5=10

Step 4; well this compound is a neutral one. Therefore charge correction doesn’t apply here.

Now the total electron count can be calculated.  

Total electron count = 8 + 10 =18

Example 02;  Mn(CO)5 Br

Step 1; Mn belongs to the d block of the periodic table. [Ar]3d54s2

Step 2; dⁿ configuration = d⁷

Step 3; Each carbonyl donates 2 electrons. 2*5=10

           Bromine donates one electron and therefore total = 11

Step 4; well this compound is also a neutral one. Therefore charge correction doesn’t apply here too.

Now the total electron count can be calculated.  

Total electron count = 7 + 11 =18

Example 03;  Mn-Mn(CO)5 

Step 1; Mn belongs to the d block of the periodic table. [Ar]3d54s2

Step 2; dⁿ configuration = d⁷

Step 3; Each carbonyl donates 2 electrons. 2*5=10

           Metal- metal bond donates one electron and therefore total = 11

Step 4; here the effect of the charge doesn’t apply.

Now the total electron count can be calculated.  

Total electron count = 7 + 11 =18

References;

https://en.wikipedia.org/wiki/Organometallic_chemistry

http://www.chemohollic.com/2016/08/18-electron-rule.html