Another important application of symmetry involves the relationships between the molecules in a unit cell. The organic compound,

crystallizes in a unit cell that contains two molecular units. These two molecules are related by a crystallographic center of symmetry (sometimes, also referred to as an “inversion center”). Click on “center”.

The center of symmetry inverts each atom through a point that has fractional co-ordinates ½, ½, ½. Thus, to solve the total three dimensional structure of the crystal, only the crystallographically independent part of the structure (in this case, one molecule) has to be located.

Other unit cells, depending on the intricacy of the crystallographic symmetry, may have two or four or eight or more molecules in the unit cell.

Compound 9163

To rotate the cell, move the cursor inside the java frame while holding down the (left) mouse button.