Zigzag Chains of Alternating Atoms in A(2)AuBi (A = Na, K) and K2AuSb. Synthesis, Structure, and Bonding

The polar intermetallic phases A(2)AuBi (A = Na (I), K (II)), and K2AuSb (III) were obtained by direct reaction of the elements at elevated temperatures in niobium ampoules. The three isotypic compounds extend the prominent A(2)MP(n) (M = transition metal; P-n = group 15) structure family. Single-crystal X-ray diffraction experiments show that these phases (I / II / III) crystallize in the orthorlionibic space group Cnicin (No. 63), with a = 9.447(2) / 10.632(2) / 10.450(2) angstrom; b = 7.700(2) 7.918(2) / 7.857(2) angstrom; c = 5.849(1) / 6.597(1) / 6.501 (1) angstrom; V = 425.4(2) / 555.4(2) / 533.8(2) angstrom(3), respectively, and Z = 4 The simple structures, which contain zigzag chains of linear two-bonded gold atoms and acute angles (64 to 76 degrees) at two-bonded antimony or bismuth, can readily be rationalized with the Zintl-Klemm concept. TB-LMTO calculations Show distinct band gaps at E-F, and analyses of DOS and COHP curves show optimized Au-Pn bonding, appreciable Au-Au interactions across the chains. aid covalent interactions between A and Pn atoms. The observed structural preference over an isoelectronic NaTl type structure, the cation influences. and site coloring were investigated with VASP and EHTB calculations.