Hydrated Lithium, Sodium And Ammonium Borate, Hydrothermal Synthesis, Crystal Structure And Its Thermal Chemistry

Because the boron atoms coordinate with oxygen not only in four-fold coordination(tetrahedral, BO₄) but also in three-fold coordination(triangular,BO₃),there are many kinds of borates with complex structures,which leads to the source as functional materials.In this thesis,we have synthesized some borates of lithium,sodium and ammonium under the hydrothermally and solvothermally conditions,and further characterized by chemical analysis,elemental analysis,FT-IR, XRD and TG-DTA.The crystal structures of new borates have been determined by the single crystal X-ray diffraction.The standard molar enthalpies of formation of those borates have been measured.Five borates,Li₃B₅O₈(OH)₂,Li₈[B₁₆O₂₆(OH)₄]·6H₂O,Na₂[B₄O₅(OH)₄]·2.5H₂O, [(CH₃)₂NH₂]₂[B₅O₆(OH)₄]₂·[HCON(CH₃)₂]and[NH₃CH₂CH₂NH₃]₂[B₁₄O₂₀(OH)₆],have been synthesised under the hydrothermally and solvothermally conditions.The compound Li₃B₅O₈(OH)₂ crystallizes in the tetragonal space group P4₃2₁2 with unit cell dimensions a=6.8506(9)(?), b=6.8506(9)(?),c=14.5601(15)(?),β=90°,V=683.32(15)(?)3,Z=4.The compound Li₈[B₁₆O₂₆(OH)₄]·6H₂O belongs to the P(?) triclinic space group,with the following unit cell parameter:a=8.484(2)(?),b=12.069(3)(?),c=13.696(3)(?),β=86.617(3)°,V=1340.6(6)(?)³,Z=2. Na₂[B₄O₅(OH)₄]·2.5H₂O crystallizes in the trigonal system,space group R3₂ with unit cell dimensions a=11.153(12)(?),b=11.153(12)(?),c=21.22(2)(?),β=90(4)°,V=2286(4)(?)³,Z=3.The compound[(CH₃)₂NH₂]₂[B₅O₆(OH)₄]₂·[HCON(CH₃)₂]is triclinic,space group C2/c with unit cell dimensions a=13.771(2)(?),b=11.5375(19)(?),c=17.512(3)(?),β=106.689(2)°,V=2665.1(7)(?)³,Z=4. The compound[NH₃CH₂CH₂NH₃]₂[B₁₄O₂₀(OH))6]is monoclinic,space group P(?) with unit cell dimensions a=8.567(14)(?),b=8.932(15)(?),c=10.106(16)(?),β=97.013(19)°,V=674.7(19)(?)³,Z=1.The molar enthalpies of solution of the synthetic samples of Li₃B₅O₈(OH)₂, Li₈[B₁₆O₂₆(OH)₄]·6H₂O,α-Na₂B₅O₈(OH)·2H₂O,β-Na2_B5O₈(OH)·2H₂O,(NH₄)₂B₈O₁₃·5.5H₂O and (NH₄)₂B₈O₁₃·6H₂O,in 1mol·L^-1 HCl(aq) have been determined by microcalorimeter at the 298.15K, respectively.The standard molar enthalpies of formation of these borates were obtained through designing thermochemical cycles.The research results of this thesis enrich the contents of borate chemistry,and provide synthetic methods and physic-chemical data for the application of some borates,which are of significance to the exploitation of borates material.