Tracing the pathway toward decomposition: Crystal structure of Ag3(PO2NH)3 and K3(PO2NH)3 as a function of temperature

Trimetaphosphimates are both molecular model systems for oxonitridophosphates and oxonitridic glasses as well as precursors for their syntheses. The decomposition of both K-3(PO2NH)(3) and Ag-3(PO2NH)(3) afford amorphous products. Analysis of the atomic displacement parameter as a function of the temperature revealed a higher increase just before decomposition, especially with respect to stretching vibrations. This is more pronounced for the P3N3 ring in Ag-3(PO2NH)(3), indicating that the ring is predetermined for decomposition, whereas there are no conspicuous sites in the potassium compound. Libration corrections for trimetaphosphimate anions result in rather small changes of bond lengths, most pronounced for P-O bonds at high temperatures.