Synthesis and characterization of methylammonium phosphates as crystalline approximants for anhydrous, low melting phosphate glasses

• Published in: RSC advances Vol. 9; no. 4; pp. 1822 - 1830
• Main Authors: Mangstl, Martin, Wied, Jan Konrad, Weber, Johannes, Pritzel, Christian, Trettin, Reinhard, Schmedt Auf der Günne, Jörn
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 01.01.2019; The Royal Society of Chemistry
• Subjects: Approximants; Chemistry; Crystal structure; Crystallinity; Glass transition temperature; High temperature; NMR spectroscopy; Organic chemistry; Phase transitions; Phosphate glass; Phosphates; Phosphorus pentoxide; Quantum chemistry; Rietveld method; Short range order; Synthesis; X ray powder diffraction
• ISSN: 2046-2069; 2046-2069
• DOI: 10.1039/C8RA07736C

Low-melting methylammonium phosphate glasses are synthesized from crystalline starting agents. To this end crystalline tris(methylammonium) cyclotriphosphate [CH NH ] P O , was synthesized by a novel and simple synthesis route from P O and -methylformamide. It, undergoes an irreversible phase transition to methylammonium -polyphosphate [CH NH ]PO . The crystal structure of the -polyphosphate was solved and refined from X-ray powder diffraction data by the Rietveld method using constraints obtained by solid-state P and H NMR spectroscopy. This compound crystallizes in a triclinic space group with = 13.2236(9), = 7.8924(6), = 4.6553(2) Å, = 91.068(4), = 87.840(5) and = 106.550(3)°. Quantum chemical calculations confirm that the obtained structure lies at an energetic minimum. Finally the reaction of tris(methylammonium) cyclotriphosphate and P O into methylammonium phosphate glass is presented. The synthesized, water-free phosphate glass shows a very low glass transition temperature of 33 °C, which was verified by dynamic scanning calorimetry and NMR. The chain-like crystal structure of the high-temperature methylammoniumphosphate [CH NH ]PO serves as an approximation for the short-range order of the glass.