The importance of lone pairs to structure and bonding of the novel germanium nitridophosphate GeP2N4

Abstract

We report the first characterization of a newly synthesized germanium nitridophosphate, GeP₂N₄. GeP₂N₄ is structurally distinct from all other known MP₂N₄ systems (M = Be, Ca, Sr, Ba, Mn, Cd) due to the presence of Ge²⁺ lone pairs that reside within rings of PN₄ tetrahedra. The Ge atoms bond covalently with three nearest-neighbour nitrogen atoms in a trigonal pyramid. It also forms a lone pair, which we directly visualize via the calculated electron density. An additional nitrogen site solely participates in bonding within PN₄ tetrahedra. We model the effect of how various defects perturb the electronic states in the vicinity of the band gap, and interrogate the presence of defects via X-ray excited optical luminescence (XEOL). This reveals the presence of nitrogen vacancies. In addition, we probe the electronic states of GeP₂N₄ with synchrotron-based X-ray spectroscopy to determine the band gap, which is similar to a DFT calculated value.