Ternary gallide Zr7Pd7–Ga3+ (0 ≤ x ≤ 1.8): Synthesis, crystal and electronic structures

The new ternary compound Zr 7 Pd 7- x Ga 3+ x (0 ≤ x ≤ 1.8) was synthesized by arc melting the elements under argon and subsequent annealing the ingots at 870 K for 720 h. The polycrystalline samples were characterized by powder X-ray diffraction (XRD) and the crystal structure of the compound was determined from single crystal X-ray diffraction data. Zr 7 Pd 7 Ga 3 crystallizes with a ternary version of the Zr 7 Ni 10 type of structure exhibiting statistical mixtures of palladium and gallium atoms on three crystallographically independent nickel sites ( oS 68, Cmce , a = 12.997(3), b = 9.623(2), c = 9.630(2) Ǻ, Z = 4, R 1 = 0.033, w R 2 = 0.067 for 719 unique reflections with I o > 2 σ(I o ) and 48 refined parameters). The crystal structure of Zr 7 Pd 7 Ga 3 is represented by a 3D Pd–Ga framework built of sinusoidal layers of Pd and Ga stacking along the b axis sandwiching the Zr atoms. The homogeneity range of the compound Zr 7 Pd 7– x Ga 3+ x has been refined from powder XRD and EDX data: 0 ≤ x ≤ 1.8; variation of the lattice parameters is the following: a = 13.0174(8)–12.904(3), b = 9.6306(8)–9.559(8), c = 9.6348(8)–9.700(5) Å. Electronic structure calculations have been performed for an idealized model Zr 7 Pd 10 as well as a model compound Zr 7 Pd 6.5 Ga 3.5 revealing that the Ga-free Zr 7 Pd 10 is significantly destabilized by strong Pd–Pd anti-bonding interactions. Substitution of Pd by Ga reduces those, stabilizing Zr 7 (Pd,Ga) 10 which features strong heteroatomic bonding between Zr and the Pd/Ga substructure, putting it into the class of polar intermetallics. Sinusoidal Pd/Ga layers stacking along the b axis in the crystal structure of Zr 7 Pd 7–x Ga 3+x . • Alloy formation in the Zr–Pd–Ga system have been investigated at 870 K. • The new ternary gallide Zr 7 Pd 7-x Ga 3+x (0 ≤ x ≤ 1.8) has been identified. • The crystal structure of Zr 7 Pd 7-x Ga 3+x (0 ≤ x ≤ 1.8) has been established. • The electronic structure and bonding patterns of Zr 7 Pd 7-x Ga 3+x (0 ≤ x ≤ 1.8) have been calculated and analyzed.