Question
Chemistry Question on coordination compounds
The atomic numbers of Cr and Fe are respectively 24 and 26, which of the following is paramagnetic with the spin of the electron :
A
[Cr(CO)6]
B
[Fe(CO)5]
C
[Fe(CN)6]–4
D
[Cr(NH3)6]+3
Answer
[Cr(NH3)6]+3
Explanation
Solution
The correct option is (D) : [Cr(NH3)6]+3
Out of CO, CN −and NH3, increasing field strength is NH3<CN−<CO Cr has 24 electrons, Fe→26 electrons. Fe2+ has 24 electrons and Cr+3 has 21 electrons. The 4 unpaired electrons in Cr and Fe can pair up because of the strong field ligand CO . CN−also strong field ligand. So, 4 electrons in Fe2+ also pair up. Though NH3 is a strong field ligand, only one electron remains in Cr+3.So no case of pairing here and [Cr(NH3)6]3+ is paramagnetic.