In: Chemistry
Which of the following species is least likely to function as a ligand in a transition-metal coordination compound?
a. BH3
b. CO32–
c. H2O
d. NF3
e. Cl–
Ligand must be an electron-rich species for functioning as a ligand in a transition-metal coordination compound.
Lewis structure of given species are shown below.
| s.no. | Species | Lewis structure | electron rich or deficient | 
| a | BH3 | ![]()  | 
deficient | 
| b | CO32– | ![]()  | 
rich | 
| c | H2O | ![]()  | 
rich | 
| d | NF3 | ![]()  | 
rich | 
| e | Cl– | ![]()  | 
rich | 
From above structures it is clear that 
 is least likely to function as a ligand in a transition-metal
coordination compound because central atom of 
 is electron-deficient  or only 6 electrons around boron
(should 8 i.e. incomplete octet).
Therefore, option (a) is correct.