Prior Likelihoods and Space-Group Preferences of Solvates

For
a range of organic solvents, the likelihood of the solvent
forming solvates has been estimated using the recrystallization solvent
(RS) data in the Cambridge Structural Database (CSD). Although RS
data are viewed with caution by some crystallographers, most of the
likelihood estimates are shown to have good precision. Strong trends
are apparent in the results. For example, high likelihoods are found
for aromatic solvents with electron-withdrawing substituents and low
likelihoods for acyclic aliphatic hydrocarbons. Results for different
CSD subsets, such as organic and metalloorganic, are highly correlated.
The likelihood that a solvent will form solvates is almost always
higher when the solvent is part of a mixture than when it is pure.
The likelihood of two solvents forming a heterosolvate (i.e., both
solvents in the structure) can be well estimated by the product of
the likelihoods of the solvents forming normal solvates (i.e., only
one solvent in the structure). The space-group preferences of solvates
vary significantly with the nature of the cocrystallized solvent.
Those of nonsolvates vary significantly with the solvent(s) from which
they were crystallized. Solvents with inversion centers favor solvate
crystallization in centrosymmetric space groups, and solvents with
2-fold rotational symmetry promote crystallization in space groups
with 2-fold proper rotational axes. The inclusion of cyclohexane and
carbon tetrachloride in a lattice can facilitate crystallization in
trigonal and tetragonal space groups, respectively. Our results can:
(a) guide solvent selection when solvates are undesired; (b) assist
in predicting solvate formation, e.g., using Bayesian algorithms;
(c) assist in the choice of space groups for solvate crystal structure
prediction; and (d) suggest ways in which solvent incorporation can
be used to influence space groups.