Synthesis And Property Research Of Novel Open Framework Zinc Phosphites And Iron Phosphites

After the discovery of Stilbite by Cronstedt in 1756, open-framework materials have been developed rapidly by the efforts of several generations of inorganic synthesis chemists. Because of their many potential applications, the mainly research area of open-framework including silicates, germinates, phosphates, phosphites, phosphonates, arsenates, borates, sulfates and selenites et al. continues to be exciting, such as using the extra-large pore framework to participate in the organic and biological macromolecules reactions and the chiral framework to support asymmetric catalysis.Recently, a new class of open-framework metal phosphites has been developed by employing the pyramidal phosphite units HPO₃^2- to replace the tetrahedral phosphate groups PO₄^3-. This new class of materials has attracted much attention due to their novel skeletal composition and features including extra-large pores, chiral and helical structure. Research and investigation has been focused on applications of open-framework materials in the areas of optics, magnetic chemistry, electrochemistry, catalytic chemistry et al. To date, numerous of metallic elements such as Al, Be, Ga, In, Co, Fe, V, Nd, Ni, Mn, Zn et al. have been used in the synthesis of metal phosphites.Among the open-framework metal phosphites, the zincophosphites constitute an important family which exhibits rich structural and compositional diversity. To date only a few zincophosphites are reported to possess helical features. Such as the 2-D layered zincophosphite |C₅H₆N₂|[ZnHPO₃] with left and right helical chains and 3-D pillared layered zincophosphite FJ-15 with 1D helical chains as pillares. Thus, the design and synthesis of zincophosphites with helical or chiral structures are of current interest and of great challenge. One useful approach to prepare inorganic helical materials is by incorporating helical or chiral organic molecules as structure-directing agents (SDAs) in the synthesis. The nature and functionality of the organic SDAs is one of the most important factors when synthesizing open-framework materials. Furthermore, the synthetic mechanism of such materials is a subject of current research, as it is not well understood. Additionally, there are several examples in literature in which small and rigid organic ligands are used to construct 3D hybrid zincophosphite frameworks. As compared to zincophosphites, there are only a few iron phosphites exist, which also plays an important role in the open-framework metal phosphites, due to both the complex magnetic properties and various valance of the iron element.The purpose of this doctoral dissertation is to synthesis and research of novel open-framework zinc phosphites and iron phosphites continuously and systematically by using hydrothermal and solvothermal methods.1. A new three-dimensional (3D) zincophosphite |Co(en)₃| [Zn₄(HPO₃)₅(H₂PO₃)] (1) has been solvothermally synthesized by using a racemic mixture of a chiral cobalt complex Co(en)₃Cl₃ as SDA. The structure of compound 1 consists of ZnO₄ tetrahedra and HPO₃ pseudo-tetrahedra, giving rise to a 3D structure with a 4.6.8-net and 10-MR channels. The metal complex molecules with both theâ–³andΛenantiomers, sit in the 10-MR channels. Also there are left-handed and right-handed helical chains in the structure which have been templated by the SDA. The notable stereospecific correspondence between the metal complex and inorganic framework is attributed to the hydrogen bonding between the host framework and the guest molecules.2. A new layered zinc phosphate-phosphite |C₆H₁₆N₂| [Zn₄(PO₄)₂(HPO₃)₂]·H₂O (2) was hydrothermally synthesized by using a racemic mixture of a chiral organic template 2-methyl-5-pentanediamine (MPMD) as SDA. Compound 2 consists of Zn-centered units and P-centered units, giving rise to a layered structure with a 4-, 6-net. Both theâ–³andΛenantiomers of the chiral template molecules stay between the adjacent layers. Compound 2 also contains the left-handed and right-handed helical chains in the layer which have been formed by hydrogen bonding between the host framework and the guest molecules.3. By employing 1,4-diazabicyclo[2.2.2]octane (DABCO) as pillared ligand, a new 3D hybrid zinc phosphite [Zn₃(C₆H₁₂N₂)₂(HPO₃)₃] (3) has been solvothermally prepared. Its structure is constructed of neutral zinc phosphite layers, which are composed of ZnO₃N tetrahedral, ZnO₃N₂ trigonal bipyramidal and HPO3 pseudo-tetrahedral. The inorganic layers pack in an ABAB sequence with the DABCO ligands as pillars, thus generating a 3D hybrid framework. It is worth noting that compound 3 exhibits 1D hexagonal 12-MR channels with extra-large pore (diameter about 1.0 nm×1.0 nm). Topological analysis shows that compound 3 is an unprecedented 3, 4, 5-connected network. The study of surface photovoltage spectroscopy (SPS) shows compound 3 possesses an unusual photoelectronic property. The photoluminescence spectra shows a main fluorescence peak at 411 nm, which can be assigned as ligand-to-metal charge transfer.4. Introducing the F^- anion as a mineralizer and the diethylenetriamine (DETA) molecule as SDA, a novel open-framework iron (III) phosphite |C₄N₃H₁₄|[Fe₃(HPO₃)₄F₂(H₂O)₂](4) has been hydrothermally synthesized. The structure of compound 4 consists of HPO₃ pseudo-tetrahedra and {Fe₃O₁₄F₂} trimer building units. The assembly of these building units generates a 3D inorganic framework with intersecting 6-, 8-, and 10-ring channels. The DETA cations are located in the 10-MR channels and linked by hydrogen bonds. The M?ssbauer spectrum shows that this compound exhibits two crystallographically independent iron (III) atoms. The magnetic investigation shows the presence of antiferromagnetic interactions.5. By using the achiral organic amine 1,4-diazabicyclo[2.2.2]octane (DABCO) as the SDA and F- anion as a mineralizer, a new 3D iron phosphite |C₆H₁₂N₂|_0.5[Fe_0.5^IIIFe_0.5^II(H₂O)₂(HPO₃)F_0.5]·0.5H₂O(5) has been solvothermally synthesized. Compound 5 possesses multi-directional intersecting helical channels made from the {Fe₂P₂O₁₂F} secondary building units (SBUs), which are strictly made up of FeO₅F octahedra and HPO₃ pyramidal tetrahedral, and the DABCO molecules are located in the"free space"of the intersecting channels. The study of circular dichroism, M(o|¨)ssbauer spectrum and the magnetic susceptibility measurement of compound 5 are still in progress.