Physical Chemistry, KILU, Lund University, P.O. Box 124, SE-22100 Lund, Sweden.
Phys Chem Chem Phys. 2019 Mar 20;21(12):6732-6742. doi: 10.1039/c8cp05682j.
The aqueous behaviour of the anionic octa-tetramethylammonium substituted cubic silsesquioxane, [N(CH3)4]8[Si8O20], was studied with quantitative 29Si-NMR. This molecule partially fragments in aqueous solutions, forming several smaller entities. The most abundant silica species are the monomer, dimer, cyclic trimer, cyclic tetramer and double three-ring. Higher concentrations are required in order to prevent complete fragmentation of the cubic structure. Additives such as alcohols and tetraalkylammonium salts have a stabilising effect on the cubic silsesquioxane, unlike sodium salts that destabilise it. A high concentration solution, containing the non-fragmented molecule as well as entities resulting from fragmentations, was investigated with neutron scattering coupled with modelling, using empirical potential structure refinement (EPSR). The modelling reveals that TMA+ ions coordinates to all different silica species, with approximately three TMA+ per cube. These are located at the faces of the cube.
研究了阴离子八甲基铵取代的立方倍半硅氧烷[N(CH3)4]8[Si8O20]在水中的行为，采用定量 29Si-NMR 进行研究。这种分子在水溶液中部分断裂，形成了几种较小的实体。最丰富的硅物种是单体、二聚体、环状三聚体、环状四聚体和双三环。需要更高的浓度以防止立方结构的完全断裂。与破坏立方倍半硅氧烷的钠盐不同，醇和四烷基铵盐等添加剂对立方倍半硅氧烷具有稳定作用。使用经验势能结构精修（EPSR），通过与建模相结合的中子散射，研究了包含未断裂分子以及由断裂产生的实体的高浓度溶液。建模表明，TMA+离子与所有不同的硅物种配位，每个立方体内约有三个 TMA+。这些位于立方的表面。
