Syntheses, Structures And Characterizations Of Open-framework Germanates Built Up From Ge-O Clusters

Inorganic microporous materials play an increasingly important role in the fieldof industrial applications, due to their porous structures and unique properties incatalysis, ion-exchange, adsorption, and separation. The synthesis and design of newopen-framework materials with novel framework structures and new chemicalcompositions have attracted considerable interest.As the analogue of silicon, germanium is of particular interest in the constructionof open-framework structures. The average Ge–O bond lengths (1.76) aresignificantly longer than the average Si–O bond lengths (1.61), which favors smallerGe–O–Ge bond angles (130) than Si–O–Si bond angles (145). The flexiblegeometrical factor is necessary for the formation of certain building units, such as3-rings and double four rings, which are desirable to form open-framework structureswith extra-large pore channels and low framework density.Unlike silicon which is usually tetrahedrally coordinated, germanium can befour-, five-, or six-coordinated to oxygen atoms as a result of its larger ionic radius.GeO₄tetrahedra, GeO5square pyramids or trigonal bipyramids, and GeO6octahedrahave been observed in the structures of open-framework germanates. Combining thedifferent polyhedral units can form well-defined cluster-building units, such as Ge5X18(Ge5), Ge7X19(Ge7), Ge8X20(Ge8), Ge9X26-m(Ge9), and Ge10X28-m(Ge10)(X=O, OH,F, m=01). These large Ge-O cluster building units can be linked to each otherthrough O atoms to form various open-framework structures with large pore sizes andlow framework densities. Typical compounds, such as SU-M, SU-MB, ASU-12,ASU-16, SU-12, FDU-4, SU-8, SU-44, SU-61, and ASU-21, are all built up fromthese complicated Ge O clusters. On the other hand, the open-framework structurescan be considered as being constructed from introducing different cluster buildingunits into a3-D net, as predicted by G. Férey based on the concept of "scalechemistry". Many new open-framework germanates with extra-large pore channelsand low framework density can be designed by using the building units of Ge–Oclusters.This PhD thesis is focused on the syntheses, structures, and characterization of open-framework germanates by combining different types of cluster-building units.Under the solvothermal conditions, we have successfully synthesized several novelopen-framework germanates by using organic amines as structure directing agents(SDAs). The corresponding structural features and the topological types are analyzedand summarized.1. A novel open-framework germanate oxide|C₆N₂H₁₈|₃₀[Ge₉O₁₈X₄]₆[Ge₇O₁₄X₃]₄[Ge₇O_14.42X_2.58]₈[GeX₂]_1.73(X=OH, F)(named asJU-84or JLG-12) has been prepared under solvothermal conditions. Its structure isbuilt from strict alternation of Ge₇and Ge₉clusters, and consists of the largest30-ringchannels along the [001] direction. The free diameters are13.0×21.4for the30-ring channels. The framework density of JU-84is9.3Ge/10003, which is one ofthe lowest among the known open-framework. On the other hand, the framework ofJU-84can be considered as being constructed from introducing the Ge₇and Ge₉clusters into the csq-a or csq net. Many new extra-large pore open-frameworkgermanates could be designed by introducing the large Ge–O clusters into other3-Dnet, based on the powerful concept of "scale chemistry".2. A novel silicogermanate|NH₃CH₂CH₂NH₃|₃[Ge_6.2Si_0.8O₁₅(OH)]₂[Ge_0.7Si_3.3O₈](named as SU-JU-14, Stockholm University-Jilin University-Number14) has beensolvothermally synthesized by using a simple ethylenediamine as SDA. Its structure isbuilt up from both (Ge,Si)7clusters and unbranched zweier double chains. The(Ge,Si)7clusters are connected to each other to form24-ring channels along the c-axis,and further connected by the unbranched zweier double chains to form athree-dimensional framework structure containing intersecting9-,10-,12-and24-ring channels. The free diameters are19.5×3.8for the24-ring channels. Theframework density of SU-JU-14is13.7T/10003. The crystal structure of SU-JU-14is somewhat disordered, resulted from the intergrowth of stacking faults of the layeredarrays with two different configurations along the a-axis. The successful structuredetermination exemplifies the use of single-crystal XRD to solve disordered structuresthat exhibit diffuse scattering. The successful synthesis of SU-JU-14suggests furtheropportunities for making novel silicogermanates with extra-large pores by choosingsimple amines as templates which can be of great interest.3. A new chain-like germanate compound|[Ni(dien)₂]3(H₂O)3|[Ge₇O13F5]2(named as JU-85, dien=diethylenetriamine) has been solvothermally synthesized byusing various Ni(dien)₂2+cations as the structure-directing agent. Its structure isconstructed from dissymmetric Ge₇chains built from diagonally linked Ge₇clusters.Compared with its structural analogue FJ-6, JU-85contains less complex cations anddifferent host-guest assembly. The cooperative non-bonding effect of Ni(dien)₂2+cations is believed to be the reason causing the formation of dissymmetric Ge₇chains.4. A novel layered germanate compound|(C₆N₄H₂₁)₂|[Ge₇O₁₄F₆](denoted asJU-86) has been solvothermally synthesized. Its structure consists of dissymmetric 4.6-net sheets built up from chiral Ge₅clusters. It is interesting that half of the4.6-netsheets in JU-86are constructed from right-handed Ge₅clusters and the other half areconstructed from left-handed ones. Right-handed and left-handed4.6-net sheets arestacked alternately along the [001] direction. Each4.6-net sheet is sandwiched by twolayers of protonated tris(2-aminoethyl)amine molecules to form a unique pseudotriple-sheet layer through H-bonding interactions. H-bonds exist only between the trenmolecule and the4.6-net sheet within the same pseudo triple-sheet layer, and noH-bonds are found between different pseudo triple-sheet layers.5. A new double-layered germanate|(H₂dien)₃|[Ge₇O_14.5F₂][Ge₇O₁₄F₃]·(denotedas JU-90, dien=diethylenetriamine) has been solvothermally prepared by usingtetraethylene glycol as the solvent. Its structure is constructed by strict alternation oftwo unique Ge₇clusters with T4and T4P linkage modes. It contains16-ring channelswith a pore diameter of13.5along the [010] direction and10-ring channels alongthe [001] direction. The framework density of JU-90is11.2T/10003.In summary, we have successfully synthesized a series of novel germanates byintroducing the Ge–O clusters into different net structures on the basis of the conceptof "scale chemistry". This PhD thesis will provide a certain foundation for thestructural design of new open-framework germanates with extra-large pore channelsand low-framework density.