Question:
The atomic numbers of Cr and Fe are respectively 24 and 26, which of the following is paramagnetic with the spin of the electron :
The atomic numbers of Cr and Fe are respectively 24 and 26, which of the following is paramagnetic with the spin of the electron :
Updated On: Apr 21, 2025
[Cr(CO)6]
[Fe(CO)5]
[Fe(CN)6]–4
[Cr(NH3)6]+3
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The Correct Option is D
Solution and Explanation
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.
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.
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Concepts Used:
Nomenclature of Coordination Compounds
Nomenclature of Coordination Compounds is important in Coordination Chemistry because of the need to have an unambiguous method of describing formulas and writing systematic names, particularly when dealing with isomers.
We can apply the following formulas:
- On the very first the central atom is listed.
- Ligands are then listed in alphabetical order and their placement in the list does not depend on their charge.
- Polydentate ligands are also listed alphabetically. In such a case of an abbreviated ligand, the first letter of the abbreviation is used to determine the position of the ligand in alphabetical order.
- The formula for the entire coordination entity is enclosed in square brackets whether charged or not. The formulas are enclosed in parentheses when ligands are polyatomic. Ligand abbreviations are also enclosed in parentheses.
- Within a coordination sphere, there should be no space between the ligands and the metal.
- When the formula of a charged coordination entity is to be written without that of the counter-ions, the charge is indicated outside the square brackets as a right superscript with the number before the sign. For example, [Co(CN)6]3-, [Cr(H2O)6]3+, etc.
- The charge of the anion(s) balances the charge of the cation(s).