Chemistry Reference
In-Depth Information
Fig. 15 Crystal structure of TTCA showing a single sheet viewed perpendicular to the plane of
the sheet.
Dashed lines
indicate N-H
S hydrogen bonds, and different types of hydrogen bonded
array are indicated by the
green
and
red lines
Another example of structure determination of a material prepared by solid-state
desolvation concerns dehydration of the hydrate crystalline phase of chloroquine
bis-(dihydrogen phosphate) [denoted CQ(DHP)
2
] to form an anhydrous phase of
CQ(DHP)
2
. In common with many processes of this type, the anhydrous product
phase is obtained as a microcrystalline powder. The structure of the anhydrous
phase has been determined [
119
] directly from powder XRD data using the direct-
space genetic algorithm technique for structure solution followed by Rietveld
refinement. The structure solution calculation involved three independent molecu-
lar fragments, representing a total of 26 structural variables (the CQ cation was
defined by 14 variables {
x
,
y
,
z
,
t
8
}, including 8 variable torsion
angles, and each DHP anion was defined by 6 variables {
x
,
y
,
z
,
y
,
'
,
c
,
t
1
,
t
2
,
...
,
}). The
structure of the anhydrous phase exhibits several interesting contrasts with the
structure of the parent hydrate phase, most notably concerning the topology of
the hydrogen-bonded chains of DHP anions that exist in both structures. Thus,
while the hydrogen-bonded chains of DHP anions in the hydrate phase are linear,
the corresponding chains in the anhydrous phase have a zigzag topology, resulting
from changes in the mode of hydrogen bonding employed by the DHP anions
within the chain. Given the substantial structural reorganization associated with the
dehydration process, it is not at all surprising that this process is associated with the
formation of a polycrystalline product phase.
y
,
'
,
c
6.5 Structure Determination of a Multicomponent Cocrystal
The structural properties of materials containing both aryl and perfluoroaryl groups
have attracted attention in recent years because of the observed propensity for such
