Lithium Ion Motion in Lithium Nitridoborate Chalcogenides Li₅(BN₂)Ch (Ch = Se, Te)

Abstract

The compounds Li5(BN2)Se and Li5(BN2)Te were synthesized at 900 °C in a closed system utilizing weld shut niobium ampoules and obtained as white microcrystalline powders. Their crystal structures were solved and refined on the basis of single‐crystal X‐ray diffraction data with the space group I41md [a = 6.3983(4) Å, c = 11.1072(9) Å for Li5(BN2)Se and a = 6.5878(3) Å, c = 11.4382(7) Å for Li5(BN2)Te]. The temperature dependent Li+ motion was investigated by 7Li MAS NMR spectroscopy.

Crystallization of the Fundamental Tetracyanamidometallates Li4[Si(CN2)4] and Li4[Ge(CN2)4] from Polymeric Li‐T‐(NCN)‐I Precursors (T=Si, Ge)

“…Using two lithium sites, the agreement between experimental and calculated line shapes is much better, only the first order spinning sidebands are stronger in the experiment than reproduced by the calculation. Such an effect has been noted previously, [32] and has been demonstrated to arise from homonuclear 7 Li dipolar interactions [33] . An assignment of the two lithium NMR sites to the two lithium sites of the crystal structure is not possible, but usually tetrahedral sites have greater quadrupolar couplings than octahedral sites when they deviate from the ideal T d or O h symmetry [34] .…”

“…Such an effect has been noted previously, [32] and has been demonstrated to arise from homonuclear 7 Li dipolar interactions. [33] An assignment of the two lithium NMR sites to the two lithium sites of the crystal structure is not possible, but usually tetrahedral sites have greater quadrupolar couplings than octahedral sites when they deviate from the ideal T d or O h symmetry. [34] However, a simple point charge calculation [35] employing the nearest nitrogen atoms about lithium with a charge of À 1 predicts only marginal differences between the octahedral (Li1) and tetrahedral (Li2) sites: χ = 43.8 (Li1) vs. 45.9 kHz (Li2).…”