Syntheses, Structures And Properties Of Microporous Borophosphate Compounds

Inorganic microporous materials have popular applications in catalysis,adsorption, ion-exchange, separation and host-guest assemblies due to their uniquepore architectures. They constitute an important area of materials science. Thecompositional chemistry of inorganic microporous materials has been widelydeveloped, and the framework elements cover most of the transition metal and maingroup elements. Borophosphates, as a new branch of inorganic microporousmaterials, have shown fascinating structural chemistry and rich compositionalchemistry. The connections of BO₃ trigonal-plane, BO₄ and PO₄ tetrahedra result invarious anionic partial structures, including oligomeric units, chains, ribbons, layersand 3-D open frameworks. Their B/P ratios include 1/3, 1/2, 2/3, 1/1, 3/1, 5/1 and 6/1.Borophosphates have potential applications in catalytic and nonlinear opticalmaterials. They are also strong candidates of zeolite materials.In early years, most of borophosphates were obtained under high temperaturesolid state conditions. Since the first cobalt borophsophate(C₂H₁₀N₂)[CoB₂P₃O₁₂(OH)] with open-framework structures was prepared by usinghydrothermal method in 1996, about 80% open-framework borophosphates havebeen prepared by using a hydrothermal method. However, as the radii of boron atomis small, and phosphates or borates are easily formed, boric acid 'flux' method wasdeveloped, and many new compounds containing boron atoms were obtained by thismethod recently.In this thesis, several kinds of synthesis and characteriazation methods wereemployed to study metalloborophosphates. A new class of borophosphates with novelstructures and interesting properties has been prepared successfully, and the reactionconditions are investigated and discussed also. In addition, the thermal stabilities,magnetic properties and ionic conductivities of these compunds are studied in detail.The reports on manganese borophosphates are rare even though they may exhibitinteresting magnetic, spectroscopic and catalytic properties. By using a hydrothermalmethod, a new three-dimensional (3-D) open-framework manganese(II)borophosphate, [NH4]4[Mn9B2(OH)2(HPO4)4(PO4)6] (MnBPO-CJ26), has beensynthesized. Single-crystal analysis reveals that the open framework containstwo-dimensional (2-D) 8-ring channels along the [010] and [001] directions. It hasthe smallest B/P molar ratio of 1/5. Magnetic measurements indicate that thecompound exhibits a canted antiferromagnetic behavior below 8.0 K. The infiniteMn―O―Mn layers are believed to be responsible for this behavior.Transition-metal compounds with the Kagomé topology have been ofconsiderable interests because of their fascinating magnetic properties, for example,geometric frustration. To our knowledge, the borophosphates containing the Kagomélattice have never been reported even though Kagomé structures are relativelyabundant in inorganic compounds. Six new open-framework borophosphatesNa5(H3O){M3II[B3O3(OH)]3(PO4)6}·2H2O (MII = Mn, Fe, Co, Ni, Cu, Zn)(MBPO-CJ25) have been synthesized under mild hydrothermal conditions.Single-crystal analyses indicate that they are isostructural compounds. The linkagesof MO6 octahedra and PO4 tetrahedra result in a 2-D layer structure exhibiting afamous Kagomé lattice. Triborates [B3O7(OH)] act as pillars between these 2-Dlayers to construct the 3-D structure of MBPO-CJ25. They are the first examplescontaining one-dimensional (1-D) 12-ring channels anionic partial structure and anew B/P ratio of 3/2. The six compounds have high thermal stabilities. They cankeep their structures intact upon calcinations around 450 °C, respectively.Magnetic property studies reveal that there are weak antiferromagneticinteractions among the metallic centers of MBPO-CJ25 (MII = Mn, Fe, Co, Ni), andweak ferromagnetic interactions in CuBPO-CJ25. No spin frustration phenomenaobserved may be due to the larger distance between the adjacent metal atoms whichare connected by sharing conners with PO4 tetrahedra or [B3O7(OH)] triborates. Thedifferent super-superexchange interactions between CuBPO-CJ25 and the othercompounds may be ascribed to the difference of metal centers.Ionic conductivities, due to a high thermal stability and motion of sodium ions,were measured for the six compounds. FeBPO-CJ25 has the lowest activationenergies of 0.91ev and highest conductivity of 1.9×10-5 S cm-1. All the sixcompounds have higher activation energies and lower conductivities compared withthe good sodium ion conductors, such as NASICON, which indicates that Na+ ions inthese compounds can move with difficulty. Ionic conductivity investigations providea base for the investigation of electronic conductivities of borophosphate compounds.Though numerous borophosphates have been reported, the synthesis of 3-Dopen-framework borophosphates, especially tetrahedral open-framework structures,is still a huge challenge. We extended a boric acid 'flux' method to the synthesis ofmetalloborophosphates and obtained two new compounds (NH4)16[Zn16B8P24O96](ZnBP-ANA) and (NH4)16[Zn13.5Co2.5B8P24O96] (ZnCoBP-ANA) with ANA zeolitetopology, and two compounds with feldspar topology, (NH4)[ZnBP2O8] and(NH4)[ZnxCo1-xBP2O8] (x ≈ 0.2). Their structural features and synthetic conditionshave been investigated in detail. These results suggest that the boric acid 'flux'method is an effective technology to synthesize new borophosphates and borateswith zeolitic structures.Other attempts by using boric acid as a 'flux' result in two borate compounds:(C2N2H10)[B7O13H3] with zero-dimensional (0-D) isolated polyanion clusters[B14O20(OH)6]4-and (NH4)2[B10O14(OH)4]·H2O with 1-D zigzag chain structures.[B14O20(OH)6]4-is a large tetradecaborate anion which enclosed by six B3O3triborates. The extensive H-bonding interactions between the adjacent clusters resultin an interesting supramolecular network with pseudo-8-ring channels. Interestingly,the two compounds can be obtained by controlling the reaction time and temperaturein the same system. There are amounts of OH groups in the structures of bothcompounds. New compounds with higher dimensional structures could be obtainedby changing reaction conditions or adding transition metals.Dense phosphates and borates are easily formed when a hydrothermal method isused to synthesize borophosphate compounds. Mounts of experiments suggest thatadding access boric acid and a certain mount of water or acid is helpful for theformation of comopound containing boron atoms. This method has the dualadvantages of both boric acid 'flux' and hydrothermal methods. However, as thereaction mechanism keeps unknown, there is still a long way to go.