Refinement of the crystal structure of palladium gallium (1:1), PdGa

Abstract

PdGa, cubic, P2 13( no. 198), a =4.89695(6) Å, V =117.4 Å 3 , Z =4,R gt(F) =0.024, wRref(F 2 ) =0.035, T =295 K. Source of materialLarge single crystals of PdGa were obtained by Czochralski growth from the melt as described in [1]. The melt consisted of Pd (99.9 %, ChemPur) and Ga (99.99 %, ChemPur) in an atomic ratio of 45:55. The metals were pre-reacted in glassy carbon crucibles under inert argon atmosphere in ahigh-frequency induction furnace. Single crystals used in this study were obtained from the bottom of the as grown Czochralski crystal and were annealed at 800°Cfor 24 hindynamic vacuum at 10 -6 mbar prior to the X-ray diffraction experiments. For the lattice parameter determination a small part of the bottom of the large crystal was crushed and annealed as described above. WDXS measurements were performed on aC AMECA SX100 (W filament, 25 kV) with Pd50Ga50 (by chemical analysis via ICP-OES) as standard. Experimental detailsSingle crystal data were collected using aRigaku R-axis SPIDER diffractometer with monochromated Ag K a radiation. Determination and refinement of the crystal structure were performed with the SHELX-97 software [2]. Spence [3] defined the two absolute structures of the FeSi type as form A( Fe in 4a with x = 0.1358, Si in 4a with x =0.844) and form B(Fe in 4a with x = 0.8642, Si in 4a with x =0.156). Models of both absolute structures were refined for PdGa without twin model and resulted in considerable differences in R gt,A =0 .028 and Rgt,B =0 .040, respectively. Further refinement of form Aa si nversion twin resulted in aF lack parameter of 0.05(1), confirming the proper parameter set. Refining site occupancy for both atoms resulted in fully occupied sites within one e.s.d. This excludes mutual site occupation in the crystal as is expected due to the covalent interactions in the compound [4].

Intermetallic compounds in heterogeneous catalysis—a quickly developing field

“…The coordination is completed by one capping Pd atom, resulting in only one Pd–Pd contact (2.73 Å). Best Pd isolation is realized in the compound GaPd (FeSi type of crystal structure, space group P 2 1 3, a = 4.8959 Å [37]), where the first coordination sphere of the palladium atom consists exclusively of seven gallium atoms. The closest Pd–Pd contact is with 3.00 Å around 10% longer than in elemental palladium.…”

CO Adsorption on GaPd—Unravelling the Chemical Bonding in Real Space

“…The isolated Pd atoms in the crystal structure render the intermetallic compound GaPd (B enantiomer, space group P 2 1 3) in an excellent catalyst for semi‐hydrogenation of C≡C bonds . GaPd is thus a highly interesting case study for basic research as well as an attractive material for industry to remove traces of acetylene in the ethylene stream for the production of polyethylene (80×10 6 t a −1 ).…”

Physical properties of the GaPd2 intermetallic catalyst in bulk and nanoparticle morphology

“…Contrary to the GaPd 2 , the GaPd phase shows only a very narrow homogeneity range around 1:1 stoichiometry, so that it can be regarded as a line compound. The GaPd unit cell is cubic (space group P2 1 3, a ¼ 4.90 Å) [20] and contains again four formula units (Z ¼ 4) with only one Pd site (Wyckoff position 4a).…”

“…Considering the activeesiteeisolation concept to play an important role in the high selectivity, this result needs further attention. The concept is ideally obeyed for the GaPd, which realizes an FeSietype cubic crystal structure [20] where a given Pd atom possesses no other Pd atom in the first coordination sphere (Fig. 1a) and the closest PdePd distance amounts to 3.00 Å. Ga 7 Pd 3 crystallizes in the Ge 7 Ir 3 etype structure, where the first coordination sphere of Pd atoms contains also one Pd atom among Ga atoms (Fig.…”

“…1. First coordination shell around the Pd atoms in (a) PdGa [20], (b) Ga 7 Pd 3 [9], (c) GaPd 2 (the shells around Pd1 and Pd2 are shown separately) [21], and (d) Pd fcc metal [22]. 3.…”