Gallium(III)-Containing, Sandwich-Type Heteropolytungstates: Synthesis, Solution Characterization, and Hydrolytic Studies toward Phosphoester and Phosphoanhydride Bond Cleavage

The gallium­(III)-containing heteropolytungstates [Ga4(H2O)10(β-XW9O33)2]6– (X = AsIII, 1; SbIII, 2) were synthesized in aqueous acidic medium by reaction of Ga3+ ions with the trilacunary, lone-pair-containing [XW9O33]9–. Polyanions 1 and 2 are isostructural and crystallized as the hydrated sodium salts Na6[Ga4(H2O)10­(β-AsW9O33)2]·28H2O (Na-1) and Na6[Ga4(H2O)10­(β-SbW9O33)2]·30H2O (Na-2) in the monoclinic space group P21/c, with unit cell parameters a = 16.0218(12) Å, b = 15.2044(10) Å, c = 20.0821(12) Å, and β = 95.82(0)°, as well as a = 16.0912(5) Å, b = 15.2178(5) Å, c = 20.1047(5) Å, and β = 96.2(0)°, respectively. The corresponding tellurium­(IV) derivative [Ga4(H2O)10­(β-TeW9O33)2]4– (3) was also prepared, by direct reaction of sodium tungstate, tellurium­(IV) oxide, and gallium nitrate. Polyanion 3 crystallized as the mixed rubidium/sodium salt Rb2Na2[Ga4(H2O)10­(β-TeW9O33)2]·28H2O (RbNa-3) in the triclinic space group P1̅ with unit cell parameters a = 12.5629(15) Å, b = 13.2208(18) Å, c = 15.474(2) Å, α = 80.52(1)°, β = 84.37(1)°, and γ = 65.83(1)°. All polyanions 1–3 were characterized in the solid state by single-crystal XRD, FT-IR, TGA, and elemental analysis, and polyanion 2 was also characterized in solution by 183W NMR and UV–vis spectroscopy. Polyanion 2 was used as a homogeneous catalyst toward adenosine triphosphate (ATP) and the DNA model substrate 4-nitrophenylphosphate, monitored by 1H and 31P NMR spectroscopy. The encapsulated gallium­(III) centers in 2 promote the Lewis acidic synergistic activation of the hydrolysis of ATP and DNA model substrates at a higher rate in near-physiological conditions. A strong interaction of 2 with the P–O bond of ATP was evidenced by changes in chemical shift values and line broadening of the 31P nucleus in ATP upon addition of the polyanion.

本研究通过三价镓(gallium(III))离子与含孤对电子的三缺位杂多钨酸盐片段[XW9O33]9–（X = AsIII、SbIII）在酸性水溶液中反应，成功合成了两类含三价镓的二聚杂多钨酸盐多阴离子：[Ga4(H2O)10(β-XW9O33)2]6–，分别记为1（X=AsIII）与2（X=SbIII）。多阴离子1与2为同构结构，其结晶产物分别为水合钠盐Na6[Ga4(H2O)10(β-AsW9O33)2]·28H2O（记为Na-1）与Na6[Ga4(H2O)10(β-SbW9O33)2]·30H2O（记为Na-2），均结晶于单斜晶系空间群P21/c，晶胞参数分别为：Na-1：a=16.0218(12) Å，b=15.2044(10) Å，c=20.0821(12) Å，β=95.82(0)°；Na-2：a=16.0912(5) Å，b=15.2178(5) Å，c=20.1047(5) Å，β=96.2(0)°。以钨酸钠、二氧化碲(IV)与硝酸镓为原料，通过直接反应制备了对应的碲(IV)取代衍生物[Ga4(H2O)10(β-TeW9O33)2]4–（记为3）。多阴离子3以铷钠混合盐Rb2Na2[Ga4(H2O)10(β-TeW9O33)2]·28H2O（记为RbNa-3）的形式结晶，晶系为三斜晶系空间群P1̅，晶胞参数为a=12.5629(15) Å，b=13.2208(18) Å，c=15.474(2) Å，α=80.52(1)°，β=84.37(1)°，γ=65.83(1)°。所有多阴离子1~3均通过固态单晶X射线衍射(single-crystal XRD)、傅里叶变换红外光谱(FT-IR)、热重分析(TGA)与元素分析进行了结构表征；其中多阴离子2还通过183W核磁共振(183W NMR)与紫外-可见(UV–vis)光谱完成了溶液态表征。以多阴离子2作为均相催化剂，用于催化三磷酸腺苷(adenosine triphosphate, ATP)与DNA模型底物4-硝基苯基磷酸酯的水解反应，反应过程通过1H与31P核磁共振光谱进行监测。封装于多阴离子2中的三价镓中心可发挥路易斯酸协同活化作用，在近生理条件下能够以更高速率催化ATP与DNA模型底物的水解反应。当向ATP体系中加入多阴离子2后，ATP的31P原子核发生化学位移变化与谱线增宽现象，证实了2与ATP的P–O键存在强相互作用。