The crystalline sponge method updated
#MMPMID27006777
Hoshino M
; Khutia A
; Xing H
; Inokuma Y
; Fujita M
IUCrJ
2016[Mar]; 3
(Pt 2
): 139-51
PMID27006777
show ga
Crystalline sponges are porous metal complexes that can absorb and orient common
organic molecules in their pores and make them observable by conventional X-ray
structure analysis (crystalline sponge method). In this study, all of the steps
in the crystalline sponge method, including sponge crystal preparation,
pore-solvent exchange, guest soaking, data collection and crystallographic
analysis, are carefully examined and thoroughly optimized to provide reliable and
meaningful chemical information as chemical crystallography. Major improvements
in the method have been made in the guest-soaking and data-collection steps. In
the soaking step, obtaining a high site occupancy of the guest is particularly
important, and dominant parameters for guest soaking (e.g. temperature, time,
concentration, solvents) therefore have to be optimized for every sample
compound. When standard conditions do not work, a high-throughput method is
useful for efficiently optimizing the soaking conditions. The X-ray experiments
are also carefully re-examined. Significant improvement of the guest data quality
is achieved by complete data collection at high angle regions. The appropriate
disorder treatment of the most flexible ZnI2 portions of the host framework and
refinement of the solvents filling the remaining void are also particularly
important for obtaining better data quality. A benchmark test for the crystalline
sponge method toward an achiral molecule is proposed with a guaiazulene guest, in
which the guest structure (with ??100% site occupancy) is refined without
applying any restraints or constraints. The obtained data quality with R int =
0.0279 and R 1 = 0.0379 is comparable with that of current conventional
crystallographic analysis for small molecules. Another benchmark test for this
method toward a chiral molecule is also proposed with a santonin guest. The
crystallographic data obtained [R int = 0.0421, R 1 = 0.0312, Flack (Parsons) =
-0.0071?(11)] represents the potential ability of this method for reliable
absolute structure determination.
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