Synthesis And Characterization Of Low-dimensional Alkali Metal/Alkaline Earth Metal Germanophosphates

Germanophosphate,as an interdiscipline of germanate and phosphate,has been reported to have not only structural diversity but also some excellent physical and chemical properties.However,compared with other metal phosphates,the study of germanophosphates is still in developing.The research on low-dimensionnal germanophosphates is still very limited,and be urgent to enrich its structural chemistry and expand its physicochemical properties.In this paper,a series of alkali metal/alkaline earth metal germanophosphates with low-dimensional structure have been synthesized by solvothermal method.The main research contents are as follows:1.Two novel alkali metal germanophosphates,Na3[Ge(OH)(PO4)2]·2H2O and Li2Na[GeO(HPO4)(PO4)],have been synthesized by solvothermal method.Both of them crystallize in same space group Pbcm with similar infinite zig-zag germanophosphates single chains.The study of crystal structures and thermal behaviors reveals that the substitution of Li+ions for Na+ ions does significantly influence the total structural features and the water molecule contents;moreover,it also impacts on their thermal stabilities.The successful syntheses of these two compounds with similar structural feature but differing in water content and alkali metals types suggest that the replacement of alkali metal through this modified solvothermal method is an efficient strategy to prepare new metal phosphates with higher thermal stability.Moreover,to the best of our knowledge,Li2Na[GeO(HPO4)(PO4)]is the first mixed alkali metal germanophosphate up to now.2.Two kinds of alkali metal fluorogermanophosphates with polymorphism have been synthesized by solvothermal method:two Cs2GeF2(HPO4)2(CsGePOF-tri crystalizing in P-1 and CsGePOF-tet in P-4b2 space group)and two K2GeF2(HPO4)2(KGePOFc crystalizing in C2/c and KGePOF-m in C2/m space group)with polymorphism.Structural analyses indicate that:CsGePOF-tri has a one-dimensional chain-like structure,CsGePOF-tet has a two-dimensional layered structure,and their crystal structure transformation belongs to the restructuring change of polymorphism transformation;KGePOF-c crystallizes in space group C2/c,KGePOF-m crystallizes in the space group C2/m,both of them have a one-dimensional chain-like structure,their crystal structure transformation belongs to the shift-type homopolymorphic transformation.Among them,CsGePOF-tet and KGePOF-c have been reported before.Five factors,such as the amount and ratio of organic solvents,the amount of HF,the amount of H3PO4,the reaction temperature,and the reaction time,have an important influence on the separation and synthesis of homogeneous polymorphs.This is the first time that homogeneous polymorphism has been found in germanophosphate systems.3.One novel alkaline earth metal germanophosphate,Ba2Ge(OH)2(PO4)2,has been successfully synthesized by solvothermal method with triethylamine and phosphoric acid as solvents,which has one-dimensional 4-MR germanophosphate single chain structure.Thermal analysis shows that the compound has high thermal stability,and the structure of the compound collapses after 600?.