β-Li₂Zn₅: A Low Symmetric Polar Intermetallic Compound

The crystal structure of the high-temperature modification of the compound Li₂Zn₅ was determined using single-crystal X-ray diffraction data. It is the first representative of a new binary structure type with triclinic space group P1̅, where the parameters of the unit cell are a = 8.0073(3)Å, b = 11.5956(6)Å, c = 15.2956(5)Å, α = 96.39°, β = 101.92°, and γ = 108.13°, the formula sum is Li_11.748Zn_31.113, Z = 2, and CCDC deposit number is 1861780. The title compound has a pseudohexagonal motif, made of 7- and 17-atom Li-zigzag chains and continuous Zn-chains, with the the relative placement of these large aggregates violating hexagonal symmetry. The structure may be decomposed into fragments, related to the AlB₂ structure type, and could be obtained from multiplication of the unit cell, multiple substitution of Li atoms by triangles of Zn, insertion of Zn atoms, and deformation. Most structures of Li-Zn compounds, except LiZn, are highly symmetric but disordered. The possible causes of lower symmetry of β-Li₂Zn₅ were analyzed using the results of DFT calculations. β-Li₂Zn₅ shows high polarity of bonds, and Li atoms donate part of the electron density to Zn atoms.