Remarkable features in lattice-parameter ratios of crystals. II.
Monoclinic and triclinic crystals.
R. de Gelder and A. Janner
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE
2005, 61, Part 3, 296-303
Abstract:
The frequency distributions of monoclinic crystals as a function of the
lattice-parameter ratios resemble the corresponding ones of
orthorhombic crystals: an exponential component, with more or less
pronounced sharp peaks, with in general the most important peak at the
ratio value 1. In addition, the distribution as a function of the
monoclinic angle beta has a sharp peak at 90 degrees and decreases
sensibly at larger angles. Similar behavior is observed for the three
triclinic angular parameters alpha, beta and gamma, with
characteristic differences between the organic and metal-organic,
bio-macromolecular and inorganic crystals, respectively. The general
behavior observed for the hexagonal, tetragonal, orthorhombic,
monoclinic and triclinic crystals {in the first part of this series [de
Gelder & Janner (2005). Acta Cryst. B61, 287-295] and in the present
case} is summarized and commented. The data involved represent 366 800
crystals, with lattice parameters taken from the Cambridge Structural
Database, CSD (294 400 entries), the Protein Data Bank, PDB (18 800
entries), and the Inorganic Crystal Structure Database, ICSD (53 600
entries). A new general structural principle is suggested.