Syntheses, Structures And Properties Of Transition Metal Borophosphates

Inorganic microporous material constitutes a very important area of the materials science. The structure and composition of the inorganic framework have been widely developed in the past. Borophosphate, as a new branch of inorganic materials, has shown fascinating structural diversities and potential applications in optical, magnetic, catalytic and ion-exchanged aspects.At the early stage of the study of borophophates, most compounds were obtained by using high temperature solid state syntheses. Since in 1990s, the hydrothermal method was introduced into the syntheses of borophosphates, the verities and quantities have grown rapidly. Recently, boric acid flux method was developed, and some new boron-contained compounds were successfully prepared.In this thesis, boric acid flux and hydrothermal synthesis method were employed to synthesize the transition metal borophosphates. Several new borophosphates are obtained, and the synthsis conditions are investigated. In additional, the properties of the synthesized compounds are studied in detail.Among the metal borophosphate compounds, vanadium borophosphates with rich anionic structures, especially the clusters, have been reported. A new three-dimensional (3-D) open-framework vanadium (IV) borophosphate, Na₂[VB₃P₂O₁₂(OH)]·2.92H₂O (VBPO-CJ27), has been synthesized by using boric acid flux method. Single-crystal structure analysis reveals that its structure is constructed by the connection of VO₆ octahedra, PO₄ and BO₄ tetrahedra, and BO₂(OH) trigonal planes to form 3-D anionic framework containing intersecting 8-, 12- and 16-ring channels. Charge neutrality is achieved by Na⁺ ions, and the guest water molecules locate in the void space of the open framework. To the best of our knowledge, it is the first borophosphate with extra-large 16-ring openings. Interestingly, its structure features unprecedented 12⁸16⁶ super cavities. The magnetic measurement reveals that VBPO-CJ27 is paramagnetic. Ion-exchange studies show that Na⁺ ions can be partially exchanged by NH₄⁺ ions.Most of the synthesized microporous borophosphates possess small pore openings, which restrict its applications as porous materials. A new three-dimensional (3-D) open-framework manganese borophosphate, (NH₄)₆[Mn₃B₆P₉O₃₆(OH)₃]·4H₂O (MnBPO-CJ31), has been synthesized by using boric acid flux method. Single-crystal structure analysis reveals that its anionic framework structure is constructed by the connection of MnO₆ octahedra, BO₄, PO₄ and PO₃(OH) tetrahedra containing 12-ring straight channels along the [001] direction with the large free aperture of 7.105×7.138 A. Charge neutrality is achieved by NH₄⁺ ions, and the guest water molecules locate in the void space of the open framework. To the best of our knowledge, it is the first borophosphate compound, which features 3-D anionic partial structure with B/P ratio of 2/3 containing a new type of fundamental building unit (FBU). Magnetic study reveals the existence of ferromagnetic component in MnBPO-CJ31.In order to better understand the borophosphate chemistry, the polyhedra of metal atoms are usually disregarded and mainly the anionic partial structures of borophosphates will be focused on. The known borophosphate anionic frameworks can be derived from a few typical borophosphate fundamental building units with rich B/P ratios. A new layered iron borophosphate, (C₄N₃H₁₆)(C₄N₃H₁₅)_0.5[Fe₂B₄P₇O₂₆(OH)₄] (FeBPO-CJ28), with a novel B/P ratio of 4/7 and mixed-valent iron (II, III) was prepared under mild hydrothermal conditions in the presence of diethylenetriamine (DETA) as the template. Single-crystal analyses indicate that the structure comprises unprecedented anionic double layers [Fe₂B₄P₇O₂₆(OH)₄]^4- with one-dimensional 8-ring channels along the [110] direction, which are made up of FeO6, BO₄, PO₄ and HPO₄ polyhedral units. Such double layers parallel to ab plane are connected by inter-layer hydrogen bonds forming the three-dimensional (3D) supramolecular open framework with pseudo 10-ring channels along the [110] direction. Protonated DETA cations locate in the 8-ring channels and pseudo 10-ring channels to compensate the negative charge of the anionic framework. The borophosphate anionic structure is featured by a new eleven-mer fundamental building unit (FBU) [B₄P₇O₂₆(OH)₄]. The magnetic measurement reveals that FeBPO-CJ28 exhibits ferrimagnetic behavior below 10 K with a hysteresis loop at 2 K (HC = 2440 Oe, MR = 0.17μB).Organo-templated syntheses of borophosphates have attracted more and more attentions in recent years. It is found that one organic template can direct multiple different frameworks under different gel conditions. On the other hand, multiple different organic templates can also produce the same framework under suitable conditions. However, such multiple-template-one-structure phenomenon is rarely observed in the syntheses of borophosphates. Three new isostructural organo-templated transition metal borophosphates, (C₃H₁₂N₂)[MnB₂P₃O₁₂(OH)] (MnBPO-CJ30), (C₃H₁₂N₂)[FeB₂P₃O₁₂(OH)] (FeBPO-CJ30A) and (C₄H₁₂N₂)[FeB₂P₃O₁₂(OH)] (FeBPO-CJ30B) were hydrothermally synthesized by using 1,2-diaminopropane and piperazine as the template, respectively. Single-crystal X-ray diffraction analyses reveal that the framework of MBPO-CJ30 (M = Mn, Fe) is constructed from the connection of infinite loop branched borophosphate ¹_{∞}[B₂P₃O₁₂(OH)^4-] chains and MO6 octahedra, giving rise to three-dimensional (3-D) intersecting 8-, 8- and 9-ring channels along the [011], [011] and [100] directions, respectively. The negative charge of the framework is compensated by the diprotonated 1,2-diaminopropane or piperazine cations located in the 9-ring channels. Structural analyses reveal that the organic amines that have the similar structure-directing ability but differing in size and shape have an influence on the crystal symmetry as well as the pore shapes of the 9-ring channels of these isostructures. Magnetic studies reveal that MnBPO-CJ30 exhibits antiferromagnetic behavior with weak ferromagnetic component to the magnetic interactions.The syntheses of borophosphates in this work reveals that more borophosphate compounds with novel structures, as well as interesting physical properties, will be further explored, and would be good candidates for new functional materials.