Steric hindrance-dependent rational design and synthesis of three new Keggin-based supramolecular networks.

Three supramolecular architectures based on alpha-Keggin-type polyoxometalates have been synthesized hydrothermally, and their structures have been characterized by elemental analyses, infrared (IR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and single crystal X-ray diffraction structure analyses. Ni(enMe)(2)(H(2)O)(2)[Ni(enMe)(2)PW(VI)(9)W(V)(3)O(40)] x H(2)O (1) (enMe = 1,2'-propanediamine) exhibits a novel 2-D supramolecular sinusoidal layer through the interactions between transition metal complexes and 1-D covalent chains which are constructed from alpha-Keggin units bridged by transition metal complexes. Ni(enMe)(2){[Ni(enMe)(2)]Ni(enMe)(2)(H(2)O)AsW(VI)(6)W(V)(4)V(IV)(4)O(42)} x 6 H(2)O (2), representing a 3-D supramolecular framework with 1-D channels, contains the first example of a tungstate dimer with inorganic-organic composite surfaces built up from Ni(enMe)(2) cation bridges and bi-capped alpha-Keggin polyoxometalate building blocks supporting the transition metal complex. Ni(enMe)(2){[Ni(enMe)(2)]Ni(enMe)(2)(H(2)O)AsMo(VI)(4)Mo(V)(4)V(IV)(8)O(44)} x 8 H(2)O (3), showing a 3-D supramolecular framework with 1-D channels, contains the first example of a molybdoarsenate dimer formed by Ni(enMe)(2) cations bridging two neighboring tetra-capped alpha-Keggin-based molybdates that support the transition metal complex [Ni(enMe)(2)H(2)O]. The topological networks of the supramolecular frameworks of 2 and 3 are analogous. Crystal structural analysis reveals that the dimensionality and the organization of polyoxometalate building units in the solid state can be tuned by the steric hindrances of the polyanions. Both 2 and 3 exhibit intensive photoluminescence.