A rare 4-connected neb-type 3D chiral polyoxometalate framework based on {KNb24O72} clusters

Abstract

A rare 3D porous chiral polyoxoniobate framework, [Cu(en)₂(H₂O)]₂{[Cu(en)]₄[Cu(en)₂]₅ {[Cu(en)₂KNb₂₄O₇₂H₁₀]₂}·6en·70H₂O(1) (en = ethylenediamine) based on two types of isomeric {Cu(en)₂KNb₂₄O₇₂H₁₀} clusters (α-CuKNb₂₄ and β-CuKNb₂₄) has been synthesized by a hydrothermal reaction. Interestingly, the α-CuKNb₂₄ and β-CuKNb₂₄ clusters are connected by cupric complexes to form chiral helical pillars with left-handedness (L-α-CuKNb₂₄) and right-handedness (R-β-CuKNb₂₄). To our knowledge, compound 1 is the first polyoxometalate-based MOF with a 4-connected neb-type topology structure within polyoxometalate chemistry. This compound also exhibits proton conduction and strong water vapor adsorption properties.