Porous Ionic Crystals Modified by Post-Synthesis of K2[Cr3O(OOCH)6(etpy)3]2[α-SiW12O40]·8H2O through Single-Crystal-to-Single-Crystal Transformation
journal contribution
posted on 2013-08-19, 00:00 authored by Sayaka Uchida, Eri Takahashi, Noritaka MizunoPost-synthesis
modification of a porous ionic crystal proceeded via two steps (acid
treatment followed by ion-exchange) in an aqueous solution and a single-crystal-to-single-crystal
manner. Compound K2[Cr3O(OOCH)6(etpy)3]2[α-SiW12O40]·8H2O (etpy = 4-ethylpyridine) [1a] is a porous ionic
crystal with one-dimensional channels, which can accommodate guests
such as water, alcohols, and halocarbons. Crystals of 1a were immersed in an aqueous HCl solution (acid treatment), and the
etpy ligand which was exposed to the one-dimensional channel was removed
and exchanged with water. The formula of the resulting compound was
(etpyH+)2[Cr3O(OOCH)6(etpy)2(H2O)]2[α-SiW12O40]·6H2O [2a], and K+ ions, which are potential guest binding sites, were simultaneously
removed by this treatment. Reincorporation of K+ ions was
attempted by immersion of 2a into an aqueous CH3COOK solution (ion-exchange), and K2[Cr3O(OOCH)6(etpy)2.5(H2O)0.5]2[α-SiW12O40]·8H2O [3a] was formed. Increase in sorption capacity by the two-step
post-synthesis modification was confirmed by sorption isotherms and
Monte Carlo-based simulations using water as a probe molecule. The
role of K+ ions as water binding sites was confirmed by
water sorption isotherms of alkali metal ion-exchanged compounds.
