Synthesis, Magnetic Properties, and Luminescence-Assisted Structure Verification of Transition Metal and Rare-Earth Imidonitridophosphates

This study reports the synthesis of two rare-earth imidonitridophosphates and a series of 3d transition metal imidonitridophosphates (MIIIH₃P₆N₁₂ with M = V, Cr, Eu, Lu, and MIIH₄P₆N₁₂ with M = Mn, Fe, Co, Ni) by high-pressure metathesis. The crystal structures were elucidated by a combination of single-crystal and powder X-ray diffraction, elemental analysis, and vibrational spectroscopy. All compounds crystallize in the orthorhombic crystal system (transition metal imidonitridophosphates: Cmce, EuH₃P₆N₁₂: Pna2₁, LuH₃P₆N₁₂: Pbam) and feature a layered anionic network composed of vertex-sharing [PN₄] tetrahedra. Magnetic measurements indicated that Mn, Fe, Co, and Ni are in the oxidation state + II, while V, Cr, Eu, and Lu are in the oxidation state + III. Furthermore, the measurements revealed paramagnetic behavior for all compounds except LuH₃P₆N₁₂ and indications of antiferromagnetic ordering at low temperatures for NiH₄P₆N₁₂ and CrH₃P₆N₁₂. The oxidation states of Fe and Eu were further confirmed by Mössbauer spectroscopic measurements. As LuH₃P₆N₁₂ does not exhibit paramagnetic behavior, additional NMR spectroscopic measurements were conducted. Furthermore, luminescence measurements provided information that supported the structural characterization and gave insights into the ligand field strength of the coordination sphere of the metal atoms in the considered imidonitridophosphates, indicating that the [PN₄] units show weakened coordination behavior.