High-Pressure Metathesis of the M1–xPO3+4xN1–4x (x ≈ 0.05) and M0.75PO4 (M = Zr, Hf) Orthophosphates

High-Pressure Synthesis of Sc5 P12 N23 O3 and Ti5 P12 N24 O2 by Activation of the Binary Nitrides ScN and TiN with NH4 F

Multinary transition metal nitrides and oxonitrides are a versatile and intriguing class of compounds. However, they have been investigated far less than pure oxides. The compounds Sc5 P12 N23 O3 and Ti5 P12 N24 O2 have now been synthesized from the binary nitrides ScN and TiN, respectively, by following a high-pressure high-temperature approach at 8 GPa and 1400 °C. NH4 F acts as a mineralizing agent that supports product formation and crystallization. The starting materials ScN and TiN are seemingly an uncommon choice because of their chemical inertness but, nevertheless, react under these conditions. Sc5 P12 N23 O3 and Ti5 P12 N24 O2 crystallize isotypically with Ti5 B12 O26 , consisting of solely vertex-sharing P(O/N)4 tetrahedra forming two independent interpenetrating diamond-like nets that host TM(O/N)6 (TM=Sc, Ti) octahedra. Ti5 P12 N24 O2 is a mixed-valence compound and shows ordering of Ti3+ and Ti4+ ions.

The Long-Periodic Loop-Branched Chain Structure of the Oxonitridophosphate La21 P40 O46 N57 , Elucidated by a Combination of TEM and Microfocused Synchrotron Radiation

The lanthanum oxonitridophosphate La21 P40 O46 N57 was synthesized by high-pressure metathesis from partially hydrolysed LiPN2 and LaCl3 at 750-950 °C and 7-9 GPa. The combination of transmission electron microscopy (TEM) and diffraction using microfocused synchrotron radiation revealed a monoclinic crystal structure (space group P21 /n, a=14.042(4), b=7.084(3), c=41.404(10) Å, β=97.73(3)° and Z=2), which is characterized by loop-branched 21 member single chains of P(O,N)4 tetrahedra that extend along [2 0 1]. These chains are related to the loop-branched dreier single chains with dreier-ring loops in stillwellite (CeBSiO5 ). In La21 P40 O46 N57 , these chains are characterized by a complex long-periodic conformation and exhibit disorder that involves La/N and P split positions. This is an extraordinarily long periodicity with respect to branched single chains of tetrahedra. La21 P40 O46 N57 constitutes the first rare-earth oxonitridophosphate exhibiting a chain structure. Single-crystal data are consistent with electron and powder X-ray diffraction.

Nitridophosphates: A Success Story of Nitride Synthesis

Nitridophosphates and phosphorus nitrides are thoroughly investigated classes of nitrides. During thirty years of research, the methods for their synthesis evolved from the condensation of molecular precursors at moderate temperatures and ambient pressures to state-of-the-art high-pressure and high-temperature processes. Landmark breakthroughs made in recent years led to a comprehension-based proficiency in nitridophosphate synthesis that is illustrated by the large compositional and structural diversity of the nitridophosphates known today. Herein, we review the advances made in synthesis with regard to the prevalent problem of nitride synthesis: the susceptibility of nitride ions to oxidation.