Ammonothermal synthesis and characterization of alkaline-earth metal guanidinates and urea

Ogutu, George Ochola; Dronskowski, Richard (Thesis advisor); Englert, Ulli (Thesis advisor)

Aachen : RWTH Aachen University (2022)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2022

Abstract

Although the structure of deuterated urea has been known and the existence of its respective polymorphs under pressure suggested via theoretical calculations, it was possible to synthesize a novel polymorph of the deuterated urea and confirm its structure using PXRD data and IR measurements. Furthermore, the synthesis of singly deprotonated strontium guanidinate was also a success. The crystal structure solution was carried out from PXRD data and the presence of singly deprotonated guanidine anions was supported by its IR spectrum. At this stage the hydrogen positions were only calculated using DFT, however, neutron powder diffraction measurements are planned to address this issue. Doubly deprotonated calcium guanidinate was also successfully synthesized and the crystal structure solved from neutron powder diffraction data. The hydrogen atom positions are half occupied above and below the mirror plane just like in its isostructural counterpart SrC(NH)3. The crystal structure of singly deprotonated calcium guanidinate has not been successfully solved due to lack of neutron powder data. However, the first steps in this work have shown that the synthesis of this phase is possible and the final structural solution will be done with neutron powder data. Finally, the structure of Ba(CN3H4)2 has been solved from a combination of neutron powder diffraction and DFT calculations, which were necessitated due to the domination of the X-ray scattering by the heavy Ba atom from PXRD data, which resulted in a chemically dubious tetragonal structure.

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