The Long-Periodic Loop-Branched Chain Structure of the Oxonitridophosphate La(21) P(40) O(46) N(57) , Elucidated by a Combination of TEM and Microfocused Synchrotron Radiation.

The lanthanum oxonitridophosphate La(21) P(40) O(46) N(57) was synthesized by high-pressure metathesis from partially hydrolysed LiPN(2) and LaCl(3) 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 P2(1) /n, a=14.042(4), b=7.084(3), c=41.404(10)†à , 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 (CeBSiO(5) ). In La(21) P(40) O(46) N(57) , 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. La(21) P(40) O(46) N(57) constitutes the first rare-earth oxonitridophosphate exhibiting a chain structure. Single-crystal data are consistent with electron and powder X-ray diffraction.