Synthesis And Characterization Of The Novel Vanadium Phosphite

Materials with open-framework structures are of great interest due to their rich structural chemistry and the potential applications in separation, absorption, ion-exchange, and catalysis. In these materials, metal phosphates constitute one of the largest families. The diversity in crystal architectures of metal phosphates was mainly derived from the utility of various organic templates and the substitution of metal ions such as transition metal ions for Al ions. Vanadium phosphates can be one of the representatives of the transition metal phosphates. The continuing interest in the design and synthesis of vanadium phosphate comes from not only their fundamental chemistry which is characterized by unusual structural complexity and concomitant diversities of electronic and magnetic properties, but also their practical application as catalysts and inorganic ion exchangers.In recent years, people tried to synthesis new open-framework compounds through changing the"anion"to open a new field for microporous compounds. A new change in the synthesis of phosphorus-based microporous materials focuses on the incorporating of pseudo-pyramidal phosphite group [HPO3]2- as a possible replacement for the traditional tetrahedral phosphate group [PO4]3- as the basic building unit and a lot of transition metal phosphites have been prepared under mild hydro- or solvothermally conditions. It is well known that the pseudo-pyramidal phosphite group [HPO3]2-, different from phosphate group [PO4]3-, only links three adjacent cations via P–O–M (M = metal) bonds, so it provides variety and novelty to the structures. Organically templated metal phosphites reserve much room for novel open- framework crystals, just like the extensively studied metal phosphates, in which numerous novel structures with one-, two-, and three-dimensional frameworks have been discovered for years. Since the vanadium phosphites with piperazinium cations as structurally directing agents were synthesized under hydrothermal conditions by Zubieta and co-workers, a number of new organically templated vanadium phosphites has been prepared successfully. In this thesis, under mild hydrothermal / solvothermal synthesis conditions, we first successfully prepared four vanadium phosphites and one vanagyl vanadate with different organic amine molecules as template agents: V2(HPO3)3 (1) , [V(HPO3)2]·H3O (2) , (C3H10N2)·[V4F2O2(HPO3)4]·2H2O (3), (VⅣO)(VⅤO4)·0.5(C3N2H12) (4) and (C5N2H13) [VO(H2O)]3(HPO3)4·H3O (5) .Compound 1 is a new 3D framework vanadium (III) phosphite microporous material with one-dimensional 4,12- member ring channels. The construction of 3D open-framework structure in the compound 1 may be viewed as the assembly of V2O9 dimers and HPO3 pseudo-pyramids. Two V2O9 dimers which constructed from two face-sharing VO6 octahedra connected through three HPO3 groups and this connective way is the first to be found in both vanadium phosphates and phosphites. It is noteworthy that compound 1 is a new example of a 3D open-framework vanadium phosphite, in which the vanadium atoms are at the +3 oxidation state exclusively. The two-dimensional layer structure of compound 2 only has 4- member ring windows.The crystal structure of compound 3 may be viewed as the connection from the infinite one-dimensional [V2F2(HPO3)2] chains and V(1)O5 square-pyramids as linkers to form the three-dimensional open-framework with multi-dimensional intersecting 8, 10-membered ring channels, and two free water molecule and one disordered organic amine molecule reside in the channels. The adjacent V(2)O4F2 octahedra are linked through their fluoride vertex to form the infinite V-F-V linear chain which has a zigzag–V–F–V–F–V– backbone, and the pseudo-pyramid HP(1)O3 and HP(2)O3 groups are grafted to this chain giving rise to a new 1D [V2F2(HPO3)2] chains which is an analog of the tancoite chain.The compound 4 is an intercalated vanadyl vanadate. The structure corresponds to a two-dimensional compound, with organic and inorganic layers alternating along the c axis.The compound 5 is a 3D vanadium phosphite with 16 membered ring channels. The 3D framework structure of compound 5 is built by the corner-sharing VO5(H2O) octahedra and HPO3 pseudo-pyramid. The 3D structure may be viewed as complex V–P–O layers linked through the double chains consisting of V(3) and P(4) (type-A) into a pillared motif with 16-polyhedra channels. This type-A chain is built by edged-fused 4-ring through -1 symmetry at the center of the 4-ring resulted in alternatively corner-shared VO5(H2O) octahedra and HPO3 pseudo-pyramid. Within the complex V–P–O layer, we further dissected out another type of chain (type-B) consisting of V(1), P(1), V(2), and P(3).Herein, we discussed the syntheses, structural features and some properties of these novel compounds and summarize the rules of synthesis. Our investigation show that it is possible to prepare structural complex open-framework vanadium phosphite possessing cavity size, limiting apertures, and framework densities rivaling those of the most open zeolites and aluminophosphates under appropriate reaction conditions.