The effective volumes of waters of crystallization: general organic solids

Abstract

Using a list of compatible hydrate/anhydrate pairs prepared by van de Streek and Motherwell [CrystEngComm (2007), 9, 55–64], we have examined the effective volume per water of crystallization for 179 pairs of organic solids using current data from the Cambridge Crystallographic Structural Database (CSD). The effective volume is the difference per water molecule between the asymmetric unit volumes of the hydrate and parent anhydrate, and has the mean value 24 Å3. The conformational changes in the reference molecule between the hydrate and its anhydrate are shown in two figures: one for a relatively rigid standard organic molecule and (in the supplementary file) one for a more flexible linear molecule. Using data from Nyman and Day [Phys. Chem. Chem. Phys. (2016), 18, 31132–31143], we have also established a generic volumetric coefficient of thermal expansion of organic solids with a value of 147 ± 56 × 10−6 K−1. There is a significant number of outliers to the data, negative, near zero, and large and positive. Some explanation for the existence of these outliers is attempted.

Ammonium Metatungstate, (NH4)6[H2W12O40]: Crystallization and Thermal Behavior of Various Hydrous Species

“…It is very unlikely that a single water molecule per α-Keggin anion increases the cell volume by 89 Å 3 ( V / Z ) (from 927 to 1016 Å 3 ), since one additional crystal water molecule accounts for an increase of the cell volume of about 23 Å 3 (Figure ). This volume is in very good agreement with a current data evaluation study that gives a mean value of 24 Å 3 per water molecule in pairs of hydrous/anhydrous compounds . A similar reasoning can be made with respect to the reported cell volume of AMT-4 which considerably differs from that determined for AMT-4 in the current work.…”

Molecular Inclusion of Small Aging Products into the Hexanitrohexaazaisowurtzitane (CL‐20) Lattice: Part II, Polymorph Dependence

“…For reference, the 1.7 % and 3.1 % volume change for the β and ɛ CL-20 anhydrate/hydrate pairs corresppond to 26 Å 3 and 46 Å 3 , respectively, while this value for α CL-20 (hydrate form of CL-20) is 7.3 Å 3 . A mean value for the anhydrate/hydrate volume difference for organic solids was reported to be 24 Å 3 [51].…”

Preference of High-Nitrogen-Content Compounds to Form Hydrates and the Tandem Contacts of Azide Groups

“…Therefore, the factors controlling the formation of hydrates and solvates in general are intensely investigated. The formation of hydrates is associated with the small size of the water molecule and with the hydrophilic properties of the host compounds. , Owing to the H-donor and H-acceptor properties, different types of hydrogen bonds can be formed by water molecules, which stabilize the structures. Hydration is a characteristic of some compounds, while others, although similar, can exist only as anhydrates.…”