Syntheses, Structures And Properties Of Metal Lodate

Since the discovery of microporous aluminophosphates AlPO4-n in 1982, crystal engineering of organically templated open-framework materials has provoked significant interest in their new structure architectures and potential applications in the fields of photochemistry, electromagnetism, catalysis, and sorption. An astonishing variety of inorganic frameworks templated by organic species in the systems of M/O, M/Si/O, M/P/O, M/As/O, M/S/O, M/Se/O, M/Te/O (M = metal) were reported. The anionic in those systems has developed from tetrahedral coordination group (such as silicate, phosphate and sulphate) to pseudo tetrahedral coordination group (such as phosphite and selenite). In order to extend the field of the system, one could search other tetrahedral or pseudo tetrahedral coordination groups, and might focus on iodate. Iodate anion, with nonbonded electron pairs, has a pyramidal geometry, which facilitates the formation of crystallographic noncentrosymmetric (NCS) structures when iodate anions are incorporated into crystalline materials. The materials with NCS structure are of great interest due to their potential nonlinear optical, piezoelectric, pyroelectric, and ferroelectric properties. Materials containing units in asymmetric coordination environments are of current interest owing to their technologically important properties such as second-harmonic generation (SHG), piezoelectricity, ferroelectricity, and pyroelectricity. In addition to having asymmetrically coordinated units, materials exhibiting these properties must also be crystallographically noncentrosymmetric (NCS). In a seminal paper by Kurtz and co-workers it was established that the successful preparation of NCS materials was often dependent on the combination of three key structural features. First, anions with a nonbonding, but stereochemically active, pair of electrons such as selenite or iodate have a tendency to align in the solid state to create polar structures. Second, transition metals have already been recognized as being susceptible to distortion from idealized octahedral symmetry. These distortions can be cooperative and lead to noncentrosymmetric (NCS) structures. Finally, large cations such as K⁺, Cs⁺, and Rb+ have a propensity for residing in sites where they form contacts with eight or more anions in an acentric environment. While there is no guarantee that the combination of these features will yield NCS structures, the tendency for this to be true is certainly apparent from extensive reviews of this area. Considering these properties, one would expect iodate pyramidal to be able to play a role similar to that of selenite pyramidal that constructs the inorganic framework and brings some new properties to the open-framework materials.We have begun to apply those ideas established by Kurtz and co-workers toШA elements'iodates in order to design and synthesize some new NCS materials with potential properties. Using hydrothermal synthesis, a series of indium iodates:α-K3In(IO3)6 (1),β-K3In(IO3)6 (2), In(OH)(IO3)2.H2O (3) and In(IO3)3 (4) from zero-dimensional, one-dimensional to two-dimensional have been prepared. compound 1 and 2 are made up of zero-dimensional units consisting of [In(IO3)6]3- anions separated by K⁺ cations. With the difference that compound 1 crystallizes in the polar space group. The polarity in the structure is imparted by the alignment of the stereochemically active lone pairs of electrons of the iodate anions along the c-axis. Second-harmonic generation of 532 nm light from a 1064 nm laser source yields a response approximately similar to that of KDP. Subtle changes in reaction stoichiometry allow for the isolation of compounds 2, 3 and 4 displaying zero-dimensional, one-dimensional to two-dimensional structures respectively.Using hydrothermal synthesis, we successfully obtained the first organically templated metal iodates: compounds 5, 6, 7 and 8. Compound 5 is simple zero-dimensional units consisting of [(Mo₂O₅(IO₃)₄)]^2- anions, Which can be described as a tetranuclear unit hanged on either side by two [IO₃] groups. The [Mo₂O₅(IO₃)₄]^2- anions are in a close connection through the water molecules and protoned pyridine cations, via hydrogen bonds and intermolecular actions. Compound 6 is built up from [MoO₆] octahedra and [IO₃] pyramids to two-dimensional layers, in which 4,4′-bipy molecules and water cations are located, forming strong hydrogen bonds with the inorganic framework, leading to pseudo three-dimensional structure. Compound 7 is one-dimensional ribbons containing {[(UO₂)(IO₃)₃](IO₃)}^2- anions and charge neutrality is achieved by the protoned 4,4′-bipy cations, which reside between two ribbons, forming hydrogen bonds with the inorganic framework and resulting in pseudo two-dimensional structure. Compound 8 is zero-dimensional units consisting of [In(IO3)6]3- anions and separated by potassium, water and ethylenediamine cations. Strikingly, it possesses helical hydrogen bonds formed by organic amine templates, water molecules and inorganic network. Using hydrothermal synthesis, we successfully obtained organically coordinated metal iodates: compounds 9, 10, 11, 12, 13 and 14. Compounds 9 and 10 possess one-dimensional chains with repeat units of alternative corner sharing of [VO₄N₂] octahedra and [IO₃] pyramids. compounds 11 and 12 possess two-dimensional layered structures, with the former consisting of [In(H₂O)(IO₃)₅]^2- clusters and [(2,2′-bipy)In(IO₃)]²⁺ chains, and the latter consisting of [In(H₂O)(IO₃)₅]^2- clusters and [(1,10-phen)In(IO₃)]²⁺ chains. Compound 13 is a one-dimensional ribbon built up of [IO₃] pyramids, [GaO₄N₂] octahdra and distinct [I₂O₆] units, and featuring interesting left and right helical chains. Compound 14 has a one-dimensional chain-like structure constructed by the alternation of [GaO₄N₂] octahedra and [IO3] pyramids.