Unveiling the Arsenic‑Oxygen Bond’s Nature Through Quantum Crystallography: Bridging to Chemical and Piezoelectric Properties

Bridging the gap between chemical bond properties and the macroscopic properties of a compound has always been a challenge. In this project, we set out to address two key questions: First, is there any relationship between the properties of the arsenic–oxygen bond and piezoelectricity? Second, is the arsenic atom in the arsenate anion hypervalent? To explore these questions, we studied a set of ten periodic and molecular arsenic oxides and collected high-resolution X-ray single-crystal datasets for them. We employed quantum crystallography and complementary bonding analysis to answer our questions. Our results from geometrical and topological analysis classify all arsenic-oxygen bond types as weaker than a single covalent bond, with stabilization largely provided by electrostatic attraction. From an orbital perspective, negative hyperconjugation plays the key role in bond stability, and we observed only a minor contribution from the d-orbitals of arsenic, effectively ruling out the concept of arsenic hypervalency. From a localization perspective, the electrons are either localized on the arsenic atom itself or on the As–O bond. The most intriguing breakthrough from this study is the observed connection between the magnitude of the dipole moment in the arsenic–oxygen bond and the material properties. Specifically, the As–O bond dipole moment reaches its maximum in gallium arsenate, a known piezoelectric material. This suggests that while other bonding properties between gallium arsenate and the other compounds may be similar, the As–O bond dipole moment in gallium arsenate plays a decisive role in shaping its unique macroscopic (piezoelectric) properties.