title: The crystalline sponge method updated.
abstract: 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.
authors.affiliation: Department of Applied Chemistry, Graduate School of Engineering, The University of Tokyo, and ACCEL (JST) , 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
authors.forename: Manabu
authors.initials: M
authors.lastname: Hoshino
authors.affiliation: Department of Applied Chemistry, Graduate School of Engineering, The University of Tokyo, and ACCEL (JST) , 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
authors.forename: Anupam
authors.initials: A
authors.lastname: Khutia
authors.affiliation: Department of Applied Chemistry, Graduate School of Engineering, The University of Tokyo, and ACCEL (JST) , 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
authors.forename: Hongzhu
authors.initials: H
authors.lastname: Xing
authors.affiliation: Department of Applied Chemistry, Graduate School of Engineering, The University of Tokyo, and ACCEL (JST) , 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
authors.forename: Yasuhide
authors.initials: Y
authors.lastname: Inokuma
authors.affiliation: Department of Applied Chemistry, Graduate School of Engineering, The University of Tokyo, and ACCEL (JST) , 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
authors.forename: Makoto
authors.initials: M
authors.lastname: Fujita
keywords: chemical crystallography; crystalline sponge method; metal–organic frameworks; porous materials