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Nentwig, Markus; Kloss, Simon D.; Neudert, Lukas; Eisenburger, Lucien; Schnick, Wolfgang; Oeckler, Oliver (2019): The Long-Periodic Loop-Branched Chain Structure of the Oxonitridophosphate La21P40O46N57, Elucidated by a Combination of TEM and Microfocused Synchrotron Radiation. In: Chemistry-A European Journal, Vol. 25, No. 63: pp. 14382-14387
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The lanthanum oxonitridophosphate La21P40O46N57 was synthesized by high-pressure metathesis from partially hydrolysed LiPN2 and LaCl3 at 750-950 degrees C and 7-9GPa. The combination of transmission electron microscopy (TEM) and diffraction using microfocused synchrotron radiation revealed a monoclinic crystal structure (space group P2(1)/n, a=14.042(4), b=7.084(3), c=41.404(10)angstrom, beta=97.73(3)degrees and Z=2), which is characterized by loop-branched 21 member single chains of P(O,N)(4) tetrahedra that extend along [201]. 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.