Using Flexible and Rigid Organic Ligands to Tune Topology Structures Based on Keggin Polyoxometalates

Three inorganic−organic hybrids based on polyoxometalate (POM), [Cu6(bbtz)6(HPM12O40)]·2H2O (M = Mo, 1; W, 2) and [Cu6(trz)2(bbtz)2(SiW12O40)] (3) (trz = 1-H-1,2,4-triazole, bbtz = 1,4-bis(1,2,4-triazol-1-ylmethyl)benzene), were synthesized under hydrothermal conditions, and structurally characterized. Through the use of the flexible ligand bbtz, isostructural compounds 1 and 2 with interpenetrating structures were obtained. In compound 1, ladder-like chains exist, in which the PMo12 anions act as “middle rails”. These chains are linked by wave-like [Cu(bbtz)]nn+ lines to construct a three-dimensional (3D) framework. Two such frameworks penetrate each other to construct a 2-fold interpenetrating structure. By introducing the rigid ligand trz, compound 3 with an un-interpenetrating structure is obtained. In compound 3, two-dimensional (2D) (63)2 metal organic framework (MOF) layers exist, which are linked by Keggin anions to construct a 3D (44·62)(63)2 framework. The differences between these compounds should be ascribed to the introduction of the rigid molecule trz that plays a role in restraining the formation of interpenetrating structures.