Asymmetrical polar modification of a bivanadium-capped Keggin POM by multiple Cu-N coordination polymeric chains.

An unprecedented asymmetrically modified bivanadium-capped Keggin polyoxometalate (POM), {AsMo12O40(VO)[VO(H2O)]}.[Cu(4,4'-bipy)]5.H2O (1) (bipy = bipyridine), has been hydrothermally synthesized and structurally characterized by a routine technique. Single-crystal X-ray diffraction analysis reveals that compound 1 exhibits a unique (3,4,6)-connected 3D framework with a (6(2).8(1))2(8(3))2(6(4).8(2))2(6(1).8(14)) topology, constructed from {AsMo12O40(VO)[VO(H2O)]}5- polyoxoanions modified by six {Cu(bipy)}n coordination polymeric chains. The asymmetrical polar coordination mode has never been found in the POM chemistry hitherto. It is also the first example of the bivanadium-capped POM as an anionic template to construct a 3D framework with the highest connection number of bicapped POMs. Additionally, by just changing the length of the organic ligand, a new compound {[AsMo12O40(VO)2][Cu(bpe)]2}.[Cu(bpe)].[H2bpe].H2O (2) (bpe = bis(4-pyridyl)ethylene), has been obtained, in which the {AsMo12O40(VO)2} sections are modified by double monotrack {Cu(bpe)}n coordination polymeric chains to form a "rail-like" 1D structure.