Pronounced matrix effect in YbMo 2 Al 4 -type Ca(Au x Zn 2− x )Au 4 ( x =0.09–0.89)

Electron-poor polar intermetallics Ca(AuxZn2−x)Au4 have been synthesized through fusion of stoichiometric metals in sealed tantalum tubes at 800°C and annealing at 400°C for one week. Single crystal X-ray diffraction analyses reveal that this phase belongs to the YbMo2Al4-type structure (I4/mmm, Pearson symbol tI14), a≈6.943–7.017Å, c≈5.278–5.286Å, Z=2, with homogeneous composition range of x=0.09(1)–0.89(1). The structure exhibits a three-dimensional framework of (Au8)1/2 featuring square and octagonal channels extending in c, in which Ca and the infinite linear chains of [(Au,Zn)2]1/2 are located, respectively. Mulliken population analyses demonstrate that Zn prefers to form the linear chains in the whole homogeneous composition range, consistent with experimental observations. Crystal orbital Hamilton population (COHP) analyses reveal that the channel-to-chain Au–Zn contact has strong bonding interactions regardless of its large interatomic distance (~2.85Å), a signature of pronounced matrix effect. The last mentioned effect in YbMo2Al4-type structures is expected in case the linear chains are defined by small size atoms.