Inorganic Chemistry, Vol.58, No.7, 4657-4664, 2019
Enantiomeric Polyoxometalates Based on Malate Chirality-Inducing Tetra-Zr-IV-Substituted Keggin Dimeric Clusters
On the basis of the synergistic strategy of lacunary polyoxometalate structure-directing function and chiral ligand inducting role, two pairs of enantiomeric polyoxotungstates, (NH4)(4)(TMA)(4)[Zr-4(mu(3)-O)(2)(L-/D-mal)(2)(B-alpha-HSiW10O37)(2)] (TMA = tetramethylammonium, mal = malate (C4H5O5); L-mal for 1a, D-mal for 1b) and (NH4)(4)(TMA)(4)[Zr-4(mu(3)-O)(2)(L-/D-mal)(2)(B-alpha-PW10O37)(2)] (L-mal for 2a, D-mal for 2b), and a mesomeric polyoxotungstate, (NH4)(3)Na2K5[Zr-4(mu(3)-O)(2)(L-mal)(D-mal)(B-alpha-SiW10O37)(2)] (3), were hydrothermally synthesized. la, 2a and 1b, 2b respectively exhibit 1-D 2(1) right- and left-hand helical chains formed by hydrogen-bonding interactions, and 3 forms a 3-D (3,10)-connected framework by Na+/K+ ions with {4(18).6(24).8(3)}{4(3)}(2) topology. These homochiral compounds represent the first examples of enantiomerically pure Zr-IV-substituted Keggin POMs. In this system, {Zr-4(mu(3)-O)(2)(L-/D-mal)(2)} clusters transfer chirality from D- or L-mal to Keggin polyoxotungstate dimeric clusters, which was demonstrated by structural comparison between the homochiral architecture and mesomer as well as circular dichroism spectra of enantiomers. UV-vis diffuse reflectance spectra reveal that 1-3 are potential semiconductor materials. In addition, 1 and 2 exhibit second harmonic generation response with their response intensities of 0.8 times that of KDP.