Hydrophobic, amorphous metal–organic network readily prepared by complexing the aluminum ion with a siloxane spaced dicarboxylic acid in aqueous medium

Abstract

A less common dicarboxylic acid with siloxane spacer, 1,3-bis(carboxypropyl)tetramethyldisiloxane, whose structure is for the first time determined crystallographically, is used to coordinate aluminum through an environment-friendly preparation process, resulting in a polymeric structure of amorphous metal-organic framework (aMOF) type. The high flexibility of the spacer induced by the siloxane bond gives the polymeric product a glass transition slightly below room temperature, while the long length of the former creates the premises for collapse of the network and consequently reduced porosity. At the same time, the high hydrophobicity of the tetramethyldisiloxane fragment and its low surface energy, which causes it to migrate to the air interface, gives the network low moisture sorption capacity guaranteeing the stability of its properties in a wet environment. The particulate complex, of the order of 1-200 nm, as generated by the synthesis, proves to be suitable as filler for silicone with outstanding reinforcement effect, without significantly affecting their transparency. The presence of the dimethylsiloxane units in the structure of both the matrix and the filler ensures good incorporation of the latter without the need for special compatibility treatments.

Permethylated dinuclear Mn(III) coordination nanostructure with stripe‐ordered magnetic domains

“…The value of difference Δν = ν as ‐ ν s of 113 is lower than that found (134 cm −1 ) in the sodium salt of adipic acid [ 30 ] indicating a bidentate chelating mode as was confirmed by XRD analysis (see below). [ 31 ]…”

From Amorphous Silicones to Si-Containing Highly Ordered Polymers: Some Romanian Contributions in the Field

“…However, highly ordered, crystalline polymeric covalent structures, where siloxane motifs alternate with coordinated metal blocks, were obtained with carboxylic ligands, 1,3-bis(carboxypropyl)tetramethyldisiloxane (H 2 CX) prepared for the first time in 1999 [ 15 ], bis(p-carboxyphenyl)diphenylsilane (H 2 L 1 ), and bis(3,4-dicarboxyphenyl)dimethylsilane (H 4 L 2 ) were prepared later [ 126 ] ( Figure 9 a). They were used alone to directly coordinate the metal ions [ 127 , 128 , 129 ] or complexes of the latter with vacancies [ 55 , 99 , 130 , 131 ] or in combination with ancillary organic ligands (imidazole [ 132 , 133 ], 4,4′-bipyridyl [ 134 ], 4,4′-azopyridine [ 56 , 132 , 135 ], 1,2-di(4-pyridyl)ethylene [ 134 ], 1,10-phenanthroline [ 126 ], etc.) ( Figure 9 b) and metal ions or clusters, which allow highly directional intermolecular interactions (metal-ligand, hydrogen bonds and π-π stacking interactions).…”

“…The high degree of methylation and the siloxane bond flexibility increase the hydrophobic character of the coordination compounds. The metal-organic frameworks based on 1,3-bis(carboxypropyl)tetramethyldisiloxane with aluminum sulphate showed a moisture sorption capacity of 3.44 wt.%, much lower (about 15 times smaller) compared to the value of 50.06 wt.% recorded for aluminum fumarate prepared and analyzed in similar conditions [ 129 ].…”