Question

. (1 pt) Use the appropriate symmetry labels to give the configuration expected for trans-[Cr(en)2CI2]* in the coordinate system shown below. Z y NAIGI8

Answer 1

1. trans-( Cr(en)₂Cl₂ )⁺ , has C₄ principle axis rotation along z-axis of coordinate system, in plane of y-axis of coordinate system there is horizontal mirror-plane (σ_h ), these translates into improper rotation axis (S₄) :C₄  * σ_h =  S_4. This accounts for achiral nature for this complex ion : A molecule cannot be chiral if it possesses an improper rotation axis.

This molecule belongs to D_4h point group.

Molecule is chiral with horizontal mirror-plane , this is meso compound (internal compensation).

trans-( Cr(en)₂Cl₂ )⁺   = Meso-( Cr(en)₂Cl₂ )⁺

2. Trigonal - bipyramidal ( D_3h )

irreducible /Symmetry representation of d-orbitals: (assuming z-axis as principle axis of rotation); we shall use quadratic function in character table for it :

• dz² : A'₁ ( a'₁)
• dx²-y², dxy​​​​​​​ : E'​​​​​​​ (e'​​​​​​​ )
• dxz, dyz :E'' (e" )

Energy level diagram (in Dq) for Trigonal bipyramidal (D_3h ) Transition metal ML₅ :

ECD9) 7.01 t6 7.07DQ + O.DT ost-0 ydu (e) ce") dxz dyz -212 D2 -242 (D3h)

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