Main postulates of Aleksandr Kitaigorodskii’s theory of organic crystal structures are
revisited. The additive model of van der Waals atom-atom potentials giving rise to
‘bump-to-hollow’ close packing of low-symmetrical molecular bodies, suggested by
Kitaigorodskii, works well for molecular crystals of non-polar hydrocarbons but requires
modifications when other types of intermolecular interactions, e.g. H-bonds, have to be
taken into account. Modern amount of structural data in CSD (ca. 1 mln crystal
structures compared to 220 structures in the original Kitaigorodskii’s analysis) allows
for several corrections and partial revision of organic molecular packing theory. In
particular, ‘forbidden’ space groups are rare, but existent, in the Pareto-type rank-size
distribution P(x)~x–α where P is frequency and x is the group’s rank in the list of 230
space groups. The closeness of molecular shapes and dimensions as a main driving
force for solid solutions’ formation is strongly dominated by ‘like-attracts-like’ principle,
first noticed for ω-disubstitued alkanes in Kitaigorodskii’s book of 1983. The problem of
multiple minima of potential energy in ab initio predictions of crystal structures may be
resolved looking for Gibbs potential minima (as suggested by Kitaigorodskii and
Mirskaya in 1972) in disordered crystals. Finally, micro-segregation of similar molecular
fragments known as hydrophobic, halogenophobic, etc. cooperative effects, points to
non-additivity of weak intermolecular interactions between atoms of different elements.
The main features of contemporary organic crystallography are listed and compared
with that of crystallography of inorganic compounds.