Chemistry, Ames Laboratory
Journal or Book Title
The Na–Au–Zn system contains the two intermetallic phases Na0.97(4)Au2Zn4 (I) and Na0.72(4)Au2Zn2 (II) that are commensurately and incommensurately modulated derivatives of K0.37Cd2, respectively. Compound I crystallizes in tetragonal space group P4/mbm (No. 127), a = 7.986(1) Å, c = 7.971(1) Å, Z = 4, as a 1 × 1 × 3 superstructure derivative of K0.37Cd2 (I4/mcm). Compound II is a weakly incommensurate derivative of K0.37Cd2 with a modulation vector q = 0.189(1) along c. Its structure was solved in superspace group P4/mbm(00g)00ss, a = 7.8799(6) Å, c = 2.7326(4) Å, Z = 2, as well as its average structure in P4/mbm with the same lattice parameters.. The Au–Zn networks in both consist of layers of gold or zinc squares that are condensed antiprismatically along c ([Au4/2Zn4Zn4Au4/2] for I and [Au4/2Zn4Au4/2] for II) to define fairly uniform tunnels. The long-range cation dispositions in the tunnels are all clearly and rationally defined by electron density (Fourier) mapping. These show only close, somewhat diffuse, pairs of opposed, ≤50% occupied Na sites that are centered on (I) (shown) or between (II) the gold squares. Tight-binding electronic structure calculations via linear muffin-tin-orbital (LMTO) methods, assuming random occupancy of ≤ ∼100% of nonpaired Na sites, again show that the major Hamilton bonding populations in both compounds arise from the polar heteroatomic Au–Zn interactions. Clear Na–Au (and lesser Na–Zn) bonding is also evident in the COHP functions. These two compounds are the only stable ternary phases in the (Cs,Rb,K,Na)–Au–Zn systems, emphasizing the special bonding and packing requirements in these sodium structures.
American Chemical Society
Samal, Saroj L.; Lin, Qisheng; and Corbett, John D., "Two Homologous Intermetallic Phases in the Na–Au–Zn System with Sodium Bound in Unusual Paired Sites within 1D Tunnels" (2012). Chemistry Publications. 974.