Tetragonal I41∕amd crystal structure of Li3BN2 from dehydrogenated Li–B–N–H

We have determined the crystal structure of Li3BN2 formed by dehydrogenation of LiB0.33N0.67H2.67 from powder x-ray diffraction (XRD) data using the Rietveld method. XRD measurements indicate unambiguously that this Li3BN2 polymorph is distinct from any of the previously reported Li3BN2 phases. We find a body-centered tetragonal I41∕amd structure (space group No. 141 in the International Tables for X-ray Crystallography) with a=6.60Å and c=10.35Å. We also describe the results of first principles theoretical modeling of the body-centered tetragonal Li3BN2 polymorph as well as the tetragonal P42212 and monoclinic P21∕c Li3BN2 structures previously reported. We obtained excellent agreement between the theoretically calculated I41∕amd Li3BN2 lattice constants and atomic positions and those obtained experimentally from XRD. The approximate enthalpy of formation of the I41∕amd Li3BN2 phase is ΔH=−495kJ∕molef.u..