Recognition of Small Polar Molecules with an Ionic Crystal of α-Keggin-Type Polyoxometalate with a Macrocation

Abstract

The complexation of Keggin-type polyoxometalates [alpha-XW12O40]n- (X = P, Si, B, Co), macrocation [Cr3O(OOCH)6(H2O)3]+, and alkali-metal ions forms ionic crystals of Na2[Cr3O(OOCH)6(H2O)3][alpha-PW12O40].16H2O (1a), K3[Cr3O(OOCH)6(H2O)3][alpha-SiW12O40].16H2O (2a), Rb4[Cr3O(OOCH)6(H2O)3][alpha-BW12O40].16H2O (3a), and Cs5[Cr3O(OOCH)6(H2O)3][alpha-CoW12O40].7.5H2O (4a). The space volumes of the ionic crystals decrease in the order of 1a > 2a > 3a > 4a. The water of crystallization in 1a-3a is completely desorbed by evacuation at room temperature, while about 50% of the water of crystallization in 4a is desorbed. The respective 1a-4a after evacuation at room temperature are denoted by 1b-4b, which show the close packing of the constituent ions. The calculated cell volumes per formula decreased in the order of 1b > 2b > 3b > 4b, which would be related to the increase in n. Compound 1b sorbs various < or =C5 polar organic molecules such as 1-butanol, valeronitrile, and methyl propionate. Compound 2b sorbs ethanol, acetonitrile, and methyl formate. Compound 3b sorbs water and methanol, and 4b sorbs only water. Thus, the ionic crystals can discriminate < or =C5 polar organic molecules such as alcohols, nitriles, and esters by one methylene chain, and the decrease in n of [alpha-XW12O40]n- enables the sorption of molecules with the longer methylene chain. The nature of the sorption properties of 1b-4b can be explained by the lattice energy needed for the expansion of 1b-4b. The selective sorption properties of 1b-4b are successfully applied to the separation of mixtures of alcohols, nitriles, esters, and water.

A functionalized polyoxometalate by hexanuclear copper–amino acid coordination complexes

“…The central B atom, in the form of {BO 4 } tetrahedron, resides in the polyoxoanion of compound 1. The B-O distances varied from 1.42(4) Å to 1.67(3) Å are consistent with the results of previous study [17]. The W-O bond lengths fall into four classes: W-Ot 1.59 (3) [20].…”

“…The filtrate was kept for two months at ambient conditions, and blue block crystals of 1 were isolated in about 25% yield (based on Cu) [16]. In the IR spectrum of compound 1, the characteristic peaks at 958, 902, 819, 625, 526 and 423 cm À1 demonstrate that [BW 12 O 40 ] 5À is a Keggin structure [17].…”

An inorganic-organic compound with 1D honeycomb-like channels constructed from non-covalent linkage: synthesis and properties

“…Vanadiumsubstituted polyoxotungstates based on Keggin frameworks were synthesized [12]. Porous supramolecular compounds containing Keggin frameworks have rarely been reported [13,14]. Important goals in the preparation of porous structural supramolecular assemblies include establishing the connections between metal-organic and/or inorganic building blocks on the basis of interactions [15, 16] such as -stacking and hydrogen bonding interactions, and examining their properties such as magnetism, absorption-desorption, electro-chemistry, catalysis and so on.…”

Syntheses, crystal structures and electrochemical properties of three organic-inorganic hybrid supramolecular compounds based on copper-complex fragments and different polyoxometalates

“…So far, welldefined POMs such as P 2 W 18 O 62 5-, SiW 12 O 40 4-and PMo 12 O 40 3-have been widely used in the generation of novel functional materials. For example, Mizuno and coworkers have synthesized some novel ionic crystal compounds which have guest-inclusion properties, such as K 3 [Cr 3 O(OOCH) 6 12 O 40 ] 4-with macrocations by ionic bonds and hydrogen bonding interactions [16][17][18][19]. Cao and coworkers have prepared frameworks possessing hexagonal channels based on [SiW 12 O 40 ] 4-units in which water molecules are accommodated [20].…”