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Exercise 4: Hexachlorobenzene

Analysis of a Bending Crystal​

Initial Setup​

  1. Open the HCLBNZ11 CIF
  2. Complete the molecule
  3. Generate Hirshfeld surface with HF/3-21G electrostatic potential

Surface Analysis​

  1. Examine the electrostatic potential:
    • Rescale to ±0.025 au range
    • Note the smaller range of surface potential
    • Observe:
      • Electropositive region above ring
      • Electropositive regions at C--Cl bond extensions
      • Electronegative regions between these areas

Structure Extension​

  1. Build molecular arrangement:
    • Create molecules above/below ring using Generate External Fragment
    • Generate surfaces using Clone Surface
    • Create adjacent molecules using Generate All External Fragments
    • Note electrostatic complementarity between molecules

Deformation Density Analysis​

  1. Create Deformation Density isosurface:
    • Select Surface Generation / Deformation Density
    • Use existing HF/3-21G wavefunction
tip

Choose Resolution / Medium for faster calculation of this structured surface

note

Observe how positive electrostatic potential regions at C--Cl bond extensions correspond to electron density deficit areas (red)

Energy Analysis​

  1. Calculate molecular pair energies:
    • Return to single molecule (Reset Crystal)
    • Calculate energies for 3.8 Å cluster
    • Note strongest interaction (-33.0 kJ/mol) along b axis

Energy Framework Analysis​

  1. Generate extended structure:
    • Create unit cell molecules (2 cells along a, 3 along b)
    • Generate energy frameworks
    • Compare components:
      • Small electrostatic contribution
      • Strong dispersion interactions along b
      • Weaker inter-column interactions (also mainly dispersive)
Crystal Bending

This energy distribution helps explain the observed bending of the crystal on the (001) face [C.M. Reddy et al., Angew. Chemie Int. Ed., 12, 2222 (2006)]