The micro-structure of aqueous boric acid (H₃BO₃) solutions is of broad interest in earth sciences, geochemistry, material science, as well as chemical engineering. In the present study, the structure of aqueous H₃BO₃ solutions was studied via neutron scattering with ²H and ¹¹B isotope labelling combined with empirical potential structure refinement (EPSR) modelling. In aqueous H₃BO₃ solutions, B(OH)₃ is the dominant borate species. Density function theory (DFT) calculations show that the boron hydroxyl has a lower electrostatic potential (ESP), which makes B(OH)₃ a relatively weakly hydrated, compared with the bulk water. In the 0.95 mol L⁻¹ H₃BO₃ solution at 298 K (saturated), ∼18 water molecules enter the hydration sphere of B(OH)₃ with the hydration distance (B–O(W)) of 3.75 Å, while only 4.23 of them hydrate with H₃BO₃ as the hydrogen bond (H-bond) acceptor or H-bond donor. Both neutron scattering and DFT calculations for 2B(OH)₃·6H₂O clusters at the ωB97XD/6-311++g(3df,3pd) basis level show that B(OH)₃ forms molecular clusters in bidentate contact molecular pairs (BCMP), mono-dentate molecular pairs (MCMP), solvent-shared molecular pairs (SMP), and parallel solvent-shared molecular pairs (PSMP) in aqueous solutions. Their relative contents are both concentration- and temperature-sensitive. BCMP with the B–B distance of ∼4.1 Å is the dominant molecular pair in the aqueous solutions. Relatively less content and van der Waals interactions stabilized PSMP, with a B–B distance of ∼3.6 Å between the two parallel layers, which is a crucial species for the crystallization of H₃BO₃ from aqueous solution.

中文翻译：

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DFT和中子散射研究阐明了H3BO3水溶液的结构。

硼酸水溶液（H ₃ BO ₃）的微观结构在地球科学，地球化学，材料科学以及化学工程领域引起广泛关注。在本研究中，通过具有² H和¹¹ B同位素标记的中子散射结合经验电势结构优化（EPSR）建模，研究了H ₃ BO ₃水溶液的结构。在H ₃ BO ₃水溶液中，B（OH）₃是主要的硼酸盐物种。密度泛函理论（DFT）计算表明，羟基羟基硼具有较低的静电势（ESP），这使得B（OH）₃与散装水相比，水合较弱。在298 K（饱和）下0.95 mol L ^-1 H ₃ BO ₃溶液中，约18个水分子以3.75Å的水化距离（B–O（W））进入B（OH）₃的水化层，而其中仅有4.23个以H ₃ BO ₃作为氢键（H键）受体或H键供体的水合物。在ωB97XD/ 6-311 ++ g（3df，3pd）基水平上对2B（OH）₃ ·6H ₂ O团簇的中子散射和DFT计算都表明B（OH）₃在水溶液中形成双齿接触分子对（BCMP），单齿分子对（MCMP），溶剂共享分子对（SMP）和平行溶剂共享分子对（PSMP）的分子簇。它们的相对含量对浓度和温度均敏感。B–B距离约为4.1Å的BCMP是水溶液中的主要分子对。相对较少的含量和范德华相互作用使PSMP稳定，两个平行层之间的B–B距离约为3.6Å，这是从水溶液中结晶H ₃ BO ₃的关键物质。