A series of open-frameworks constructed from polyoxoanion clusters and copper-tetrazolate complexes: synthesis, structure and properties

Polyoxometalates (POMs) are discrete metal-oxygen clusters with different shapes, sizes, and compositions, which provides a variety of structural building units (SBUs) for making novel and robust POM-based cluster-organic frameworks. Therefore, the combination of POM clusters and metal-organic frameworks will open up a new avenue for the creation of a variety of novel functional materials. Recent years, the hydrothermal technique proved to be a particularly powerful synthetic means of making crystals of numerous organic-inorganic hybrids. In this paper, three organic-inorganic hybrid openframeworks constructed from different types of polyoxoanion cluster units and Cu-(2-ptz) (2-ptz=5-(2-pyridyl)-tetrazole) complexes, Cu₄ (2-ptz)₄ (H₂O)₇ SiW₁₂O₄₀ • 4H₂O (1), Cu₅ (2-ptz)₆ (OH) (H₂O)₃PW₁₂O₄₀ • H₂O (2), Cu₉ (μ-O)₆ (2-ptz)₆ (H₂O)₉- (H₆P₂W₁₈O₆₂) • 3H₂O (3) have been hydrothermally made and structurally characterized by elemental analyses, infrared spectrum (IR) spectroscopy, thermogravimetric (TG) analyses, ultraviolet-visable diffuse reflectance spectrum (UV-DSR), powder X-ray diffractions (PXRD), and single-crystal X-ray structural analyses, respectively. Structure analyses reveal that compounds 1~3 are three-dimensional (3-D) frameworks. The structure of 1 is built up of the isolated zigzag Cu-(2-ptz) complex segments and SiW₁₂O₄₀^4- clusters; 2 is constructed from the 2-D Cu-(2-ptz) networks and PW₁₂O₄₀^3- cluster pillars; while 3 is made of the linear Cu-(2-ptz) chains and 6 P₂W₁₈O₆₂^6- clusters. Magnetic measurements indicated that compounds 1 and 2 exhibit antiferromagnetic interactions between Cu ions, while compound 3 display ferrimagnetic coupling behavior. UV-DSR spectra indicate that compounds 1~3 are potential semiconductor materials. The successfully syntheses of compounds 1~3 not only testify that the shapes and the number of negative charges of POM anions have an important influence on the self-assembly of organic-inorganic hybrid POM-based materials, but also may open up possibilities for the design and construction of new POM-based frameworks with particular functions in the near future.