Integral lattices

Most of the sharp peaks, recently reported by Constant & Shlichta [Acta Cryst. (2003), A59, 281-282], in the frequency distribution of known tetrahedral and hexagonal-rhombohedral inorganic compounds apparently correspond to integral lattices. These are characterized by an integral metric tensor of their basis vectors (up to a unit-length factor). Integral lattices also occur in molecular forms of axial-symmetric biomacromolecules, as illustrated by a RNA quadruplex. A general tendency in nature to reduce the number of structural free parameters is conjectured.