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.