The Syntheses, Structures And Characterizations Of Novel Open-framework Germanates

Inorganic microporous materials possessing regular pore structures orcharacteristic cages/cavities play an important role in various fields, such as catalysis,adsorption-separation, and ion exchange. The designed synthesis of novel inorganicmicroporous materials with special pore structure have been becoming a frontiersubject in inorganic chemistry. Zeolites are one of the most important members ininorganic microporous materials, which have three-dimensionally four connectedstructures constructed strictly from corner-sharing TO₄（T=Si, Al, P, etc.） tetrahedra.Inorganic microporous materials also contain the zeolite-like open-frameworkmaterials built of TOn（n=3、4、5、6） primary building units. Since the1990s, thespecial chemical characteristics of germanium in constructing open-frameworkmicroporous materials and the structural diversity of germanates have attractedincreasing attention.So far,206types of zeolite frameworks have been identified by the StructureCommission of the International Zeolite Association （IZA-SC）. Among which, theGe-containing zeolites of ITQ-43（281212ring）, ITQ-44（181212ring）（IRR）, are open-framework structures with very low framework density （Frameworkdensity is the number of TO₄tetrahedra per1000A³）. ITQ-33（18×10×10ring） andITQ-37（30-ring）（-ITV） are Ge-containing zeolites possess both extra-large pore andchiral characteristics. On the other hand, according to the concept of―scalechemistry‖, the combination of4,5and6coordinated Ge-centered polyhedron canlead to the formation of some well-defined clusters including Ge₇, Ge₈, Ge₉, Ge₁₀clusters. These large cluster-building units can then be linked to each other to form avariety of open-framework structures with large pores. For example, JLG-12with 30-ring channels is built of Ge₇and Ge₉clusters, SU-M with30-ring channels is builtof Ge₁₀clusters. These zeolite or zeolite-like open-framework structures withextra-large pores have great potential in the application of shape-selective catalysis,and separation of large molecules.This thesis mainly focused on the exploring of novel open-framework germanates,two synthetic routes are utilized: one route is to synthesis in a concentrated gel systemwith H₂O/GeO₂in the molar ratio of1.5templated by quaternary ammonium, and thismethod is seldom used in the syntheses of pure germanates. The other route is tosynthesis through host-guest charge matching principles by the introduction oftrivalent metal （Al or Ga） and using in situ formed metal complexes as templates.First, we have synthesized a polycryatalline phase, named GeO-JU90. For thestructure solution of GeO-JU90, the synchrotron radiation XRPD data are collected.The structure of GeO-JU90is solved by the combination of charge-flipping algorithm,simulated annealing algorithm and EXAFS （extended X-ray absorption fine structure）characterization, which provides a powerful way for structure solution of othercomplex polycrystalline structures. In the synthesis system of GeO-JU90, anothernovel open-framework germanate GeO-JU94was obtained by adding HF. Thestructure of GeO-JU94possesses a special "open" double four-ring （D4R） buildingunits, and two of them connected with each other in the linkage mode of D4R-D4R bysharing the face of four-ring. Second, we have successfully synthesized the firstzeolite GaGeO-JU64that possesses a three-dimentional odd-numbered11-ringintersecting channel system. GaGeO-JU64has the lowest framework density （FD=9.9T/1000A³） ever achieved in oxide zeolites. The successful synthesis ofGaGeO-JU64opens the possibility of synthesizing novel zeolites with odd-numbered11-ring channels, which may hold promise for improving catalytic and molecularsieving properties. We have also reported four compounds of different chemicalcompositions that exhibit the same JST framework topology, which is builtexclusively of3-rings. Through the ICP analyses of the four compounds and their topological analyses of one unit cell, the most reasonable distribution of Al³⁺or Ga³⁺cations has been deduced. Similarly, the distributions of Be²⁺cations in zeolite OSO,another zeolite built exclusively of3-rings, can also be deduced. The main results ofthe thesis are as follows:1. A new three-dimensional open-framework germanate|(C₁₅N₂H₃₂)（NH₄）|[Ge₁₁O_21.5（OH）₄], named GeO-JU90was successfully synthesizedunder hydrothermal conditions in the system of GeO₂-quaternaryamine-H₂O（H₂O/GeO₂=1.5）. The structure of GeO-JU90is obtained by synchrotronradiation XRPD data. It revealed a complicated framework structure containing11Geatoms and27O atoms in the asymmetric unit. The framework is built of7-connectedGe₇clusters and additional GeO₃（OH） units forming a new three-dimensionalinterrupted framework with intersecting12×12×11-ring channels. The Ge K-edgeextended X-ray absorptionfine structure （EXAFS） analysis was performed to providethe local structural information around Ge atoms, giving rise to a first-shellcontribution from about4.2（2） O atoms at the average distance of1.750（8）. Theresult is in agreement with the obtained structure of GeO-JU90. This work not onlyshows one novel germanate structure but also provides a powerful way for structuresolution of other complex polycrystalline structures.2. A new three-dimensional open-framework zeolitic germanate, GeO-JU94wassuccessfully synthesized under hydrothermal conditions in the system ofGeO₂-quaternary amine-HF-H₂O （H₂O/GeO₂=1.5）. The framework is constructedfrom a new kind of opened D4R unit which combines with each other in the mode ofD4R-D4R. The D4R-D4R building units are connected with each other through3-ringand bridged oxygen atoms forming a structure with12×10-ring channels.3. A new zeolite gallogermanate|（Ni（1,2-PDAs）₃）₃₆Ni_4.7|[Ga_81.4Ge_206.6O₅₇₆]（1,2-PDA）₃=1,2-propanediamine), namedGaGeO-JU64was synthesized under solvethermal conditions using the in situ formed metal complexes [Ni（1,2-PDAs）3]2+as the structure directing agents. GaGeO-JU64isthe first example of zeolite with a three dimensional intersecting11-ring channels.The structure features two pairs of enantiomer cavities of [3¹².4³.6².11⁶].GaGeO-JU64has the lowest framework density （FD=9.9T/1000A³） ever achievedin oxide zeolites.4. A series of zeolitic alumino-/gallogermanate compounds,|M（II）（en）₃|[M（III）₂Ge₄O₁₂]（M（II）=Ni, Co, Zn; M（III）=Al, Ga; en=ethylenediamine）, has been synthesized using in situ formed [M（II）（en）₃]²⁺cations asthe structure-directing agents. These zeolitic compounds exhibit the same JSTframework topology which is built exclusively of3-rings. The frameworks of thesecompounds are constructed from M（III）-and Ge-centred tetrahedra. According toinductively coupled plasma （ICP） analyses, the ratios of M（III）/Ge are1/2in all thesecompounds. According to the ICP results and the unique structural feature of JST, themost reasonable distribution of M³⁺cations in these structures has been deduced.Similarly, the distributions of Be²⁺cations in zeolite OSO, another zeolite builtexclusively of3-rings, can also be deduced.