Daniel Guenther (Leipzig University, Germany)

High-pressure metathesis is a successful method for syntheses of intriguing nitridophosphates, e.g. LiNdP4N8 or LiPr2P4N7O3.[1] The reaction of LiPN2 and LaCl3 at either 7 GPa and 750 °C or 9 GPa and 950 °C yields the new oxonitrodophosphate La21P40O46N57 if water is present, e.g. by hydrolysis of LaCl3 or the used BN crucible. The microcrystalline product was characterized by single-crystal structure determination using microfocussed synchrotron radiation after preselecting suitable crystallites by transmission electron microscopy and electron diffraction. The compound crystallizes in the monoclinic space group P21/n with a c lattice parameter of ca. 41.4 Å. Its complicated structure is built up from vertex-sharing P(O,N)4 tetrahedra forming loop-branched chains with dreier ring branches. Lanthanum atoms are embedded between these loops. The chains are built up by 21er units. These units are interconnected either by vertex- or by edge-sharing tetrahedra; alternatively, the chain can interrupted. These different variants are described by disordered tetrahedra. An additional split position involving La and N/O atoms leads to eight different local structure variants. Tentative structure refinements in lower-symmetric space groups such as Pn, taking into account twinning where appropriate, do not result in ordered models and thus confirm the disorder.

Acknowledgements: We thank Dr. J. Wright, Dr. V. Dyadkin (ESRF, Grenoble) for their help with synchrotron measurements and the ESRF for granting beamtime (projects CH-5142 and CH-4612).

References

[1] S. D. Kloß, W. Schnick, Angew. Chem. Int. Ed. 2019, 58, 2-14.