Determine the point group of SF5Cl.
The Correct Answer and Explanation is:
The point group of SF₅Cl is C₄v.
Explanation
To determine the point group of SF₅Cl (sulfur pentafluoride chloride), we begin by analyzing its molecular geometry and symmetry elements.
1. Molecular Geometry:
SF₅Cl is a derivative of SF₆ (sulfur hexafluoride), which has an octahedral geometry. In SF₅Cl, one of the six fluorine atoms in SF₆ is replaced with a chlorine atom. This still results in an octahedral arrangement of six ligands around the central sulfur atom. However, because chlorine is different from fluorine, the molecule is no longer symmetric in all directions like SF₆.
To minimize repulsion (as chlorine is larger than fluorine), the Cl atom preferentially occupies an axial position. So the structure has a square pyramidal shape with:
- Four fluorine atoms in the equatorial plane,
- One axial fluorine above,
- One axial chlorine below the sulfur atom.
2. Symmetry Elements in SF₅Cl:
- C₄ axis: A fourfold rotation axis through the sulfur atom and perpendicular to the equatorial plane (passes through the axial F and Cl atoms).
- σᵥ planes (vertical mirror planes): Four mirror planes exist—two that pass through opposite equatorial F atoms and the axial atoms (F and Cl), and two that bisect the angles between equatorial F atoms.
- No center of inversion (i), because replacing one F with Cl breaks that symmetry.
- No horizontal mirror plane (σh), again due to the Cl substitution.
With a C₄ principal axis and four σᵥ planes, this matches the C₄v point group.
3. Why Not Other Groups?
- Oh: SF₆ has this, but SF₅Cl lacks the full symmetry.
- C₄h, D₄h: These require σh planes or inversion centers, which SF₅Cl lacks.
- C₄: Lacks the mirror planes present in SF₅Cl.
Final Answer:
Point group of SF₅Cl = C₄v.
