The structure of dimer ${\mathrm{Fe}}_2{\mathrm{Cl}}_6$ is

Explanation:

1. Chemical Formula: Fe₂Cl₆ exists as a dimer because simple FeCl₃ monomers tend to polymerize due to the Lewis acidity of the Fe³⁺ ion.
2. Structure Details:
   • The Fe₂Cl₆ molecule consists of two iron atoms connected by two bridging chloride ions.
   • Each iron atom is also bonded to two terminal chloride ions, completing its coordination sphere.
3. Bonding:
   • Each Fe atom forms two covalent bonds with two terminal Cl atoms.
   • The two Cl atoms that bridge the Fe atoms contribute to a total coordination number of 4 for each Fe atom.
   • This arrangement minimizes electronic repulsion and stabilizes the dimer structure.
4. Geometry:
   • The structure is a distorted tetrahedron around each Fe atom.
   • The Fe-Cl-Fe bond angle in the bridged part is typically less than 180°, contributing to the distortion.

Structure Representation

Key Properties of Fe₂Cl₆

Molecular Weight: Fe₂Cl₆ = 2 × Fe (55.845) + 6 × Cl (35.453) = 325.65 g/mol.

Bond Order and Oxidation State:

• Each Fe atom has an oxidation state of +3.
• The bridging chloride ions balance the coordination environment.

Why FeCl₃ Forms Dimers?

Fe³⁺ has a strong Lewis acidic character, which makes it prone to forming bonds with lone pairs on the chloride ions. Bridging chloride ions help to stabilize the system by reducing the electron deficiency around Fe³⁺.

Final Answer

The structure of Fe₂Cl₆ is a dimer with two iron atoms bridged by two chloride ions, and each iron atom is also bonded to two terminal chloride ions. This arrangement minimizes electron repulsion and stabilizes the dimer in a distorted tetrahedral geometry.