The ability for gold to reduce and act as a formal anion stems from its anomalously high electronegativity due to relativistic effects and the lanthanide contraction. In gold, the 6s and 6p orbitals are considerably contracted causing these energy levels to decrease while the enhanced nuclear shielding causes the 5d and 4f orbitals to expand. The result is a small energy difference between the 6s and 5d orbitals, which is the origin of gold’s unique properties including its distinctive color, high electronegativity, and the desire to form Au-Au bonds, called aurophilicity. In this research, we focus on synthesis of new crystal structures in the RE-Au-Sn (RE = La, Ce, Pr, Nd) ternary phase space to understand the origin and limits of forming these homoatomic interactions. All compounds were synthesized directly from the elements by arc melting, followed by annealing. The crystal structures were solved using single crystal X-Ray diffraction with the composition confirmed by Energy-dispersive X-ray spectroscopy (EDX). The structure solutions verify the presence of Au-Au bond networks with the RE atoms stuffing in the hexagonal gold network. The electronic structure and associated chemical bonding were analyzed based on COHP (crystal orbital Hamilton population) and electron localization function (ELF) analysis and indicates the polar-covalent nature of the Au interactions. These results support that in systems where gold is combined with electropositive rare-earth metals, like in RE-Au-Sn ternary phase space, there is potential to have complex intermetallic bonding including the presence of extraordinary gold-gold bonding.

Honeycomb network of Au-Au bonding in intermetallic, RE-Au-Sn (RE = La, Ce, Pr, Nd) ternary phase space

255th National Meeting (2018)

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