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

Three inorganic−organic hybrids based on polyoxometalate (POM), [Cu 6 (bbtz) 6 (HPM 12 O 40 )]·2H 2 O (M = Mo, 1; W, 2 ) and [Cu 6 (trz) 2 (bbtz) 2 (SiW 12 O 40 )] ( 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 PMo 12 anions act as “middle rails”. These chains are linked by wave-like [Cu(bbtz)] n n + 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) (6 3 ) 2 metal organic framework (MOF) layers exist, which are linked by Keggin anions to construct a 3D (4 4 ·6 2 )(6 3 ) 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.