New Si-O-P-N compounds and materials: Syntheses, structures and material properties

• Applicants: Dr. Erica Brendler; Professor Dr. Edwin Kroke
• Subject Area: Inorganic Molecular Chemistry - Synthesis and Characterisation ; Analytical Chemistry ; Solid State and Surface Chemistry, Material Synthesis ; Polymer Materials
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 509900844

Based on our interesting results in the DFG project "Fourfold vs. sixfold: coordination in phosphosilicates", this project includes the synthesis of Si-O-P-C/N compounds as well as the investigation of the influence of nitrogen on coordination of silicon in these structures. Depending on the choice of silicon reactants and reaction conditions, the use of the envisaged multifunctional aminophosphonic acids will lead to the synthesis of molecular model compounds with silatran structures as well as to the synthesis of oligomeric and polymeric materials. Proton conductivity is expected for the targeted materials, and the question of where the protons leading to conductivity are localized - in OH or NH groups - needs to be investigated. In addition to solvent-based synthesis routes, thermal reactions will also be used.In addition is planned that the reactions of phosphinic acids with silicon tetrahalogenides, which have so far led to very interesting products, including [(SiL6)4+][X4]4-"salts", will be expanded by varying the reactants.Characterization of the products will focus on solution and solid-state NMR spectroscopy. In addition to reaction tracings, various 1D and 2D solid-state NMR methods will be used. Direct excitation and cross-polarization experiments are used to detect, quantify and characterize the structural groups. Neighborhoods and links between structural elements are analyzed with hetero- and homonuclear correlation experiments (HETCOR, RFDR or BABA) and via REDOR (Rotational-Echo Double-Resonance) measurements. To improve the predictive power of the experiments with respect to nitrogen, the synthesis of 15N-labeled aminophosphonic acids will be performed. This is of particular interest with respect to the localization of protons (OH versus NH).The focus continues to be on selected material properties. In addition to investigating the thermal behavior of the Si-O-P-(C,N)-materials, their hydrolytic resistance will be analyzed. Since the polymeric products can be deposited as layers on different substrates, they have to be analyzed morphologically in more detail. Based on the Si-O-P layer structures obtained by us and proton-conducting Zr-O-P-N compounds described in the literature, the ionic conductivity is to be investigated by means of impedance spectroscopy in this project.

• DFG Programme: Research Grants