Establishing the Isostructural Platform GaPd₂‐InPd₂‐SnPd₂ to Address Electronic and/or Structural Effects

Abstract

Dedicated to Professor Josef Breu on the occasion of his 60 th birthday.The isostructural series (Ga,In)Pd 2 and (In,Sn)Pd 2 have been established and characterised. Together with the recently discovered isostructural series (Ga,Sn)Pd 2 , they form a triangle along the edges of which electronic, structural and the combination thereof on chemical and physical properties can be explored, e. g. in heterogeneous catalysis. Single-phase ternary samples of the Ga 1-x In x Pd 2 and In 1-x Sn x Pd 2 series are synthesised with x = 0.1 substitution steps. Metallography and powder X-ray diffraction are utilised to establish the phase composition of the samples and to determine how the lattice parameters vary with composition. In both isotructural series, the total volume of the unit cell increases linearly with the substitution degree x. The isostructural triangle thus constitutes an excellent material platform for decoupling electronic and structural effects, namely in catalysis, where the combination of both effects usually obscures their individual influence due to their coexistence in multimetallic catalytic materials.

Disentangling Electronic and Geometric Effects in Electrocatalysis through Substitution in Isostructural Intermetallic Compounds

“…The monotonic shift of the reflections to lower 2θ values correlates with increasing tin content and fits the expectation of a monotonic expanding unit cell as tin has a larger covalent radius than gallium. This is in line with observations on the previously reported Ga 1- x In x Pd 2 series (Figure S1), whereas in the case of the In 1– x Sn x Pd 2 series (Figure S2), the positions of the reflections remained virtually unchanged …”

“…The herein investigated intermetallic compounds InPd 2 , SnPd 2 , and GaPd 2 crystallize into the Co 2 Si type of crystal structure (space group Pnma , oP 12) and represent the binary endmembers of the isostructural ternary series in Figure . The ternary substitutional series comprise the (Ga,Sn)­Pd 2 series, together with the recently established (In,Sn)­Pd 2 and (Ga,In)­Pd 2 series …”

“…The ternary substitutional series comprise the (Ga,Sn)Pd 2 series, 33 together with the recently established (In,Sn)Pd 2 and (Ga,In)Pd 2 series. 34 Since tin and indium have extremely similar covalent radii (1.42 and 1.40 Å, respectively), the gradual substitution of indium (three valence electrons) with tin (four valence electrons) through the In 1−x Sn x Pd 2 series allows for the systematic and linear increase of the valence electron count per formula unit within the rigid band approach. 49 The electronic change is accompanied by a negligible variation of the unit cell volume by only 1.3% (V(InPd 2 ) = 195.1 Å 3 versus V(SnPd 2 ) = 197.7 Å 3 ).…”

“…The isostructural series (Ga,In,Sn)­Pd 2 shown in Figure fulfills the above requirements. The triangle comprises (Ga,Sn)­Pd 2 , which was developed to investigate influences in the semihydrogenation of acetylene, as well as the two isostructural substitutional series (In,Sn)­Pd 2 and (Ga,In)­Pd 2 …”

“…The triangle comprises (Ga,Sn)Pd 2 , which was developed to investigate influences in the semihydrogenation of acetylene, 33 as well as the two isostructural substitutional series (In,Sn)Pd 2 and (Ga,In)Pd 2 . 34 Samples of the isostructural series Ga 1−x In x Pd 2 and Ga 1−x Sn x Pd 2 were successfully synthesized as single-phase materials and tested for their catalytic properties in the electrochemical oxidation of methanol (MOR). The results are compared with the In 1−x Sn x Pd 2 series, which has been used to isolate pure electronic effects.…”