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

Abstract

The lanthanum oxonitridophosphate La21P40O46N57 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 La21P40O46N57, 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. La21P40O46N57 constitutes the first rare‐earth oxonitridophosphate exhibiting a chain structure. Single‐crystal data are consistent with electron and powder X‐ray diffraction.