Giant Polyniobate Clusters Based on [Nb7O_(22)]~(9-)Units Derived from a Nb7O_(19)Precursor

摘要

Rational self-assembly of hexaniobate Lindqvist-type precursor [HNb6O_(19)]~(7-)with soluble Cu~(2+)salts utilizing different strategies produces a series of giant polyniobate clusters, namely, (H_2en)_(1.25)[Cu(en)2(H2O)]_2-Cl4[Nb_(24)O_(72)H_(21.5)]·7H2O(1;en:ethyl- enediamine),[Cu(en)2]3[Cu(en)2(H2O)]9- [{H2Nb6O_(19)} is contained in {[({KNb_(24)O_(72)H_(10.25)}{Cu- (en)2})2{Cu3(en)3(H2O)3J{Na_(1.5)Cu_(1.5)- (H2O)8}{Cu(en)2}4]6}]·144H2O (2),K_(12)Na4[H_(23)NaO8Cu_(24)(Nb7O_(22))8]·106H2O(3),and K_(16)Na_(12)[H9Cu_(25.5)O8(Nb7O_(22))8].73.5H2O(4).Their structures were determined and further characterized by single-crystal X-ray diffraction analysis, IR and Raman spectroscopy,thermog-ravimetric analysis(TGA),and elemental analysis.Structural analyses reveal that compound 2 comprises a giant capsule anion based on a wheel-shaped cluster encapsulating a Lindqv-ist diprotonated cluster [H2Nb7O_(19)]~(6-)unit,and forms a honeycomb-like structure with the inclusion of Lindqvist-type anions [H2Nb7O_(19)]~(6-)in the holes,whereas 3 and 4 represent an un- precedented giant cube-shaped framework.All the compounds are built from [Nb7O_(22)]~(9-)fundamental building blocks.Solution Raman spectroscopy studies of 2 and 3 reveal that the solid-state structures of these polyniobate cluster anions disassemble and exist in the form of the [Nb6O_(19)]~(8-)unit in solution.Magnetic susceptibility measurement of 3 shows antiferromagnetic coupling interactions between Cu~(II)ions with the spin-canting phenomenon.