Synthesis, Crystal Structure and Li Motion of Li₈SeN₂ and Li₈TeN₂

Daniel Bräunling (1) , Oliver Pecher (2) , Dmytro Trots (3) , Anatoliy Senyshyn (4) , Dmitry Zherebtsov (5) , Frank Haarmann (6) , Rainer Niewa (7)

1 Chemie
2 CPfS - Max-Planck-Institut für Chemische Physik fester Stoffe
3 Bayerisches Geoinstitut - Bavarian Research Institute of Experimental Geochemistry and Geophysics
4 Fachbereich Material­ und Geowissenschaften
5 South Ural State University
6 IAC RWTH - Institute of Inorganic Chemistry [Aachen]
7 Anorganische Chemie

The compounds Li₈EN₂ with E = Se, Te were obtained in form of orange microcrystalline powders from reactions of Li₂E with Li₃N. Single crystal growth of Li₈SeN₂ additionally succeeded from excess Li. The crystal structures were refined using single crystal X-ray diffraction as well as X-ray and neutron powder diffraction data (I4₁md, No. 109, Z = 4, Se: a = 7.048(1) Å, c = 9.995(1) Å, Te: a = 7.217(1) Å, c = 10.284(1) Å). Both compounds crystallize as isotypes with an anionic substructure motif known from cubic Laves phases and Li distributed over four crystallographic sites in the void space of the anionic framework. Neutron powder diffraction pattern recorded in the temperature range from 3 K to 300 K and X-ray diffraction patterns using synchrotron radiation taken from 300 K to 1000 K reveal the structural stability of both compounds in the studied temperature range until decomposition. Motional processes of Li atoms in the title compounds have been revealed by temperature dependent NMR spectroscopic investigations. Those are indicated by significant changes of the ⁷Li NMR signals. Li motion starts for Li₈SeN₂ above 150 K while already being present in Li₈TeN₂ at this temperature. Quantum mechanical calculations of NMR parameters reveal clearly different environments of the Li atoms determined by the electric field gradient which are sensitive to the anisotropy of charge distribution at the nuclear sites. With respect to an increasing coordination number according to 2 + 1, 3, 3 + 1, and 4 for Li(3), Li(4), Li(2), and Li(1), respectively, the values of the electric field gradients decrease. Different environments of Li predicted by quantum mechanical calculations are confirmed by ⁷Li NMR frequency sweep experiments at low temperatures.

Mots clés: Physical Sciences

Daniel Bräunling, Oliver Pecher, Dmytro Trots, Anatoliy Senyshyn, Dmitry Zherebtsov, et al.. Synthesis, Crystal Structure and Li Motion of Li₈SeN₂ and Li₈TeN₂. Journal of Inorganic and General Chemistry / Zeitschrift für anorganische und allgemeine Chemie, 2010, ⟨10.1002/zaac.201000002⟩. ⟨hal-00552440⟩