The unit cell

The unit cell is the repeating structure found within the crystal. The unit cell may consist of a single molecule of the compound; it could contain two or more molecules in different configurations; it could have multiple molecules which differ by a symmetry operation; or in the case of a molecule posessing symmetry the unit cell might consist of a fraction of the molecule. Along with the main molecule of interest, the unit cell might additionally include other compounds, for example solvents of recrystallisation.

The unit cell does not necessarily contain the entirety of a single molecule within the cell. The unit cell often consists fragments from multiple molecules which together constitute the entire molecule.

Defining the cuboid

The unit cell is described as cuboid, a hexahedron with six faces, eight vertices and twelve edges. The cuboid is described using six parameters, three for length (a, b and c) and three for angles (alpha, beta, gamma).

Lattice system

The lattice system